Bob O’Neill on Sensors and Diagnostics in Dodge, Plymouth, and Chrysler cars of the 1980s and 1990s

bob I’m Bob Lincoln. I’m an engineer and a self-taught mechanic, and I thought I’d share a little bit of that knowledge with you here today.

I’ve been working on cars for over 30 years. I go back to the days of carburetors and breaker-point ignitions and no sensors on cars. Today’s cars have become pretty complex and it’s tough to keep up with it if you still want to do your own work.

Most of my cars are from the 1990s, and they’re in the middle of that gap between the latest technology and the more traditional stuff. But I will try to share with you some knowledge about sensors that can go wrong in the car and stop you dead, or give you a lot of grief. We’ll go through several of those right now.

This particular one is called a throttle position sensor, and this is mounted on the throttle body, on the throttle shaft. And it rotates with the throttle shaft. Inside this is a variable resister for the wiper arm, and the voltage from the car’s computer to this provides the electrical signal which changes as the throttle opens and closes. The range of voltage is typically between .8 and 4 volts with a four inch motion, and this is a sensor that helps the car decide how to set the air fuel mixture by knowing how far open the throttle is.

TPSIt can cause you a fair amount of grief if it gets the wrong signal, and normally the way these fail is they get a dead spot or intermittent spots and the wiper on this fizzes. Really it’s just a thin, brass plate across variable resistance and a little pointer arm that scrapes across it. So there’s your wear-out mechanism.

There’s three terminals, 5 volts, ground and signal. And this sometimes will set a defect code or fault code in the computer but usually not when it fails because the computers only look for too high or too low a voltage and they don’t look for any problems in-between. And that’s true of most of the sensors up until today’s. The way you can find out there’s a problem with it is with this device called a multi meter, which is a voltmeter, amp meter and an ohm meter. It does voltage, resistance and ohms – amps. And the way you can diagnose this is to cross the center terminal and one of the other terminals with the leads and look for a change in resistance, and it should be a nice clean sweep in value. You can use an analog meter which has a needle, and that could be more useful just to visually get the effect, but what you’re looking to do is see if you get any unusual resistance readings.

talks

The range on this one runs from zero to 5,000 ohms and the center pin and one of the side pins will give you the reading, and the center pin and the other side pin will give you the opposite end of the scale. So it’s zero ohms on one end and 5,000 on the other so one will increase and the other will decrease. So this is actually showing about 10 ohms on one end which is close to zero, it’ll never be exactly zero, and as I rotate this – I can do that with my thumb – that reading will change and I now get about 30… about 37 ohms. So this will crank all the way up as I rotate this. It’s about a $20 to $30 part, and it just has an electrical plug and two screws so it’s pretty simple to change. You just have to make sure that you engage the little tabs here properly when you put the new one on. But some of the symptoms that will cause are stumbling or interment idle or sometimes even a failure to start or stalls immediately after starting. So that’s one of the more common ones.

Oxygen Sensor

oxygen sensorThis one is the oxygen sensor, and again the computer uses the input from this sensor to tell how rich the exhaust is and to decide whether to add more fuel or not. And you’ll see a little probe here that screws into the exhaust manifold, and it has a zirconium sensor which puts out a voltage signal proportional to the oxygen content. So two wires, again, for signal and ground and there’s two wires for heating it up because it really doesn’t work effectively until it gets up to 600 degrees. So when the engine is too rich, it has used up all the available oxygen, the exhaust has overcome that and there’s even extra gasoline left over so the voltage will go high and the high end of the scale is .9 volts. When it’s too lean it gets down as low as .1 volts.

There’s really no effective way to test it outside of the car for most people, but what you can do is probe these wires while it’s running and you can get a signal off that and see if it’s changing. It should flutter back and forth near the midpoint, and it can change a few times a second. If you don’t see that kind of activity, it’s bad and you change it. Just unplug it and unscrew it. It’s usually in there pretty good, but there’s a socket that slips around this wiring and you can unscrew it. These are anywhere from $40 to typically $70, a dealer might get it at $100 even. They provide you with some anti-seize compound you can put on the threads. If you get any on the sensor, goodbye, you ruined it, because it contaminates it. The sulfur in that, it destroys it.

bob lincoln

A lot of people are very partial to certain brands of sensor, and Bosch has gotten a bad reputation among a number of people. I discovered why. I used it, and I had no problems with it operationally but I went to take one out of the car and the socket wouldn’t quite reach onto the hex. Its length was different. And I rounded off the socket, and there it remained stuck in the engine.

The other thing I noticed is this is the OEM brand made by Denso. It has 32 little holes stamped in it all the way around so you can get good flow through there and get an accurate reading. The Bosch sensor has eight little slits, very, very tiny slits cut through it and it just looks inherently like the airflow is not nearly as good around it and so it won’t respond as well and it can get clogged with carbon more quickly. So this is probably one where it pays to go with an OEM-type brand.

MAP

vacuum testThe MAP sensor (Manifold Absolute Pressure) is a little molded plastic device which has a vacuum to it and electrical plugs. You have 5 volts, ground and signal. And its purpose is to set the mixture also, and it basically tells the computer whether you’re at full throttle or not or somewhere in-between based on the vacuum – the engine vacuum. It’s assumed that if you’re near full throttle, you’re accelerating, there’s almost no vacuum. So there is a voltage signal that is proportional to vacuum. So when you go to full throttle, you’re up there almost 5 volts on the scale, and when the throttle’s closed or high-vacuum you’re down around ½ a volt. It’s a very linear scale.

A few things can go wrong with that sensor, and there are a couple of codes associated with it. Code 13 shows as lost vacuum, and that can be that the chip is fractured. It usually means that the hose has fallen off or split open or there’s a massive vacuum leak somewhere else in the car. I’ve even had it when the engine momentarily almost stalled, and the vacuum dropped low just because the engine was stalled and it tripped that code which would make it think it was the sensor.

Code 14 is associated with it and that’s the sensor out of range, either too high or too low of voltage. I had a failure of this on my last car and it was none of those. It turned out the sensors ripped it. It’s just a very, very thin silicon sensor in a big circuit, and it deflects back and forth over its life and it just sort of cold warped eventually and its resistance value changed ever so slightly until the voltage signal had drifted away from what it normally is. And it’s just enough so that in the mid-range of operation where you usually are, it was giving the wrong voltage to the computer so it was dumping a little extra fuel in so it was running rough and stalling, so no codes associated with that. But it dumped enough fuel in that the oxygen sensor said this thing’s running rich and it tripped the sensor for the oxygen.

So it can be a little complicated to diagnose these, so sometimes you have to kind of reason through what’s going on with the engine. That sensor is about $30 or so, $40 maybe, and again it’s just an electrical plug and a vacuum line that screws in to mount it, so it’s a five minute job to change it out. Most of them are pretty easy to reach. Sometimes they’re on the throttle body, sometimes they’re on the firewall. Few of the cars they’re tucked away inside the passenger kick pad which is tough to get at.

Hall Effect

This is a hall effect sensor, and it fires the ignition. This is inside the distributor. And this takes the place of the old breaker-point ignition, and it takes the place of the reluctors and the first electronic ignition Chrysler came up with. The sensor is called a hall effect sensor which is a little magnetic pick up, and there is a shuttered wheel that slides through on your ignition rotor and as it passes by this it breaks the magnetic field and causes a pulse here. This plug is powered up with 8 volts, and by that passing through in there, being out of there, switches the ignition back and forth. And so it sends a digital pulse back to the computer and the computer then fires the foil.

This particular one is out of my turbo car. It has one pickup for the ignition and one for the fuel injection, so you’ve got two points of failure in one device. And sure enough, the reason this is here in this box is because it failed. I was driving near home and the car started cutting out and stalling. I got it started and stalled, started and stalled and finally made it home after a dozen tries. Most people believe this hall effect sensor degrades. I don’t think it’s really true. It’s pretty much the wiring. I mean, you’ll see creases in it where the distributor cap clamps on it, and I think the primary failure really is people pinching the wires. So if you’re handy you probably could actually repair these, and I plan to repair it as a spare.

thebobs

They’re pretty skimpy on the length as it is, so I probably want to lengthen it. So I’m probably going to get some new wire. This one’s for the fuel pickup and this one’s for the ignition. They’re powered by 8 volts which comes out of the computer. We could also just have a problem with the plug being intermittent. Easy to get out, you just take the two screws off the distributor cap, you pull the rotor off and it slips right out. These go anywhere from about $60 to $120 depending on where you buy it. Some of them are a little hard to find, the turbo one in the two pickups, so that’s why I’d rather fix it and take my chances.

Connectors

brakesThis is a good time to say a word about the connectors. Sensors can and do fail, but just as often you’ll find the connections fail. These connectors are brass and they’re templated, and there’s a couple problems with that in a mobile environment like a car. One is that the contacts tend to rub against each other back and forth, back and forth, it’s just a micro-motion but it’s enough that it displaces some of that tin and then it oxidizes and insulates and you start getting intermittent contact. You can pull it out and plug it back in and get the crud out of the way and you’re fine.

There’s a couple ways to avoid problems long-term, and one is periodically clean it. Take it out like that and just clean it with a toothpick or get a brush in there. But the corrosion can also get in there just from water, and one of the best ways to avoid that is dielectric grease, and that is a non-conductive grease you can find at radio shack or a lot of automotive supply stores and you just fill the whole cavity. Just pack it in. When you plug it in, the contacts scrape against each other and that removes the grease in the contact area itself which is why it’s non-conductive but it works when you plug them together because the grease gets displaced and you’ve got metal on metal rubbing against each other, very tightly surrounded by grease.

Someone had a question a couple of years back on the forum saying dielectric grease is the worst thing to use. It’s an insulator, you can’t put that in there. It's non-conductive. Well that’s right, it blocks out everything else. But the contact ends are a tight enough fit that they force the grease out of the way and it surrounds the rest of the connection.

Questions

Is there a problem with contacts spreading? Because you’ve got a pin and sleeve, and the sleeves are sometimes spread out and you’ve got to kind of get it back in.

Exactly. And that is pretty common. As you see, these are the pins with the male contact, and the mating one is the female contact. It’s just a roll-barrel, and yep, over time they can just relax. Metal just ages and temperature changes cause them to relax or if it flexes at all. So it’s pretty hard to get in there and do much about it. If you can get needle-nose pliers in and just kind of bend it back a little tighter, pinch it down just a tiny bit, that’s a good thing to do because we really want a nice, tight connection on that. Other than that, there’s not much you can do but replace it if you have that much of a problem. But definitely…

They don’t have these connectors available for you to be able to replace one either.

You pretty much can’t buy these in most stores because the connectors made for the automotive industry are more rugged and specialized. If you’re making a million cars a year, you can go to a connector manufacturer and say I want one exactly the way I want it and it doesn’t get sold to anybody else. It’s not in the catalog necessarily. But what you can do is buy both halves of any standard connector, snip these off and make your own termination if you really get stuck and you want to do that. Just choose a good connector that’s pretty much as waterproof as you can get it to be, has a good tight seal. But that’s always an option if it’s hard to find.

Automatic Idle Speed Motor

AISLet’s see, other essentials. One other vice that can give you a problem, it’s not really a sensor per se, it’s called the air-idle speed motor, or AIS, and it’s a stepper motor with a plunger. Essentially just an electric motor that moves a plunger back and forth from the throttle body, and its purpose is pretty much that of the choke on an old carburetor. It does the same thing as a choke. It has a plunger that blocks off an air passage, so it’s just providing more or less air into the throttle passageway and it’s controlled by the computer. And it can act irrationally depending on whether there’s a connector problem or whether the computer gets bad input from one of these other sensors and tells it to run the wrong direction, whether it’s stalling out or running too rich or too lean or when you’re decelerating it may close off or open up and it’ll change the idle speed.

I had one malfunction once and it was causing the car to stay at a high idle. It would stay at about 2-3000 RPMs. I’d be coasting along at 40 miles an hour and the car’s driving itself. It acted like a stuck throttle plate, but it wasn’t. It was just this had opened up enough and let enough extra air through that the idle had just stayed up and I drove for over a mile on level ground, 40 miles an hour without it slowing down. Just coasting.

The other thing that causes that is a vacuum leak. With my current car, that happened just the throttle body loosened up on the manifold and there was enough of a vacuum leak for that that it was behaving the same way and I almost replaced the air-idle speed motor and I ended up instead going down and just tightening the bolts a little tighter and it was fixed.

Why understanding the sensors is important

Look for the simple things first, and the least expensive things, and try not to buy parts until you’re sure you really need them. It’s just a matter of knowing how these sensors all interact and what can cause the problem.

The oxygen sensor, it adjusts the fuel mixture. It only operates at about 600 degrees, so the computer ignores it the first few minutes your car is running from a cold start. So if your car won’t start, it’s impossible for this to be the cause of it. If it suddenly starts acting up two minutes into your drive, chances are it’s one of the first places you should look because now it’s suddenly looking at its input and now it’s causing problems. And it can cause bucking and stalling and poor acceleration and gas mileage to drop by over a third.

One of the diagnostic tools for the MAP sensor, you can test it outside the car and check the voltage, but the voltage versus the vacuum you can measure by applying a vacuum to it. This is a hand vacuum pump. If I block this off, you can see from the gauge I can simulate the engine vacuum on the sensor. I just plug this in the sensor, crank it up over 20 inches and then I can put 5 volts across the sensor and I can measure it with this voltmeter.

You wonder, how do we get 5 volts? If you’re an electrical engineer you sketch out a little circuit. This cost about $12 to make with Radio Shack parts. It’s a voltage regulator, and it takes this 9 volts and changes it down to 5 volts and there’s a little switch to turn it on and off, and there’s my 5 volts and my ground and I just have to find a way to hook this up to the pins and I’ve got a 5 volt power supply I can test the sensors with.

This is going to be used to test the throttle position sensor, it can be used to test the MAP sensor, or the cooling temperature sensor. And that’s the last one we have to talk about. The engine also uses a cooling temperature sensor and that screws into the thermostat housing and it is a variable resistor which changes with temperature dramatically. It’s used to set the mixture for cold operation versus hot operation. When the engine’s cold, the sensor is roughly 13,000 to 15,000 ohms and if the engine’s warm it falls down to about 1,000 ohms or even a little bit less. So it’s a steep curve. The reading changes rapidly as it warms up.

That sensor can go bad, and if it does or if it gets unplugged the computer will think the engine is cold and the reading’s gone to infinity and it’ll start putting extra fuel in to compensate. So the car will run fine when it’s cold, and when it’s hot you won’t be able to start it or it’ll run poorly or stall. That sensor you can just simply put an ohm meter across and measure the resistance. If the engine’s cold you can get a good reading, 13,000 ohms or so. When it’s warm, assuming you can run the car until it gets warm, you’ll see the reading plummet down to about 1,000 or maybe even 600 ohms and it should be a quick, smooth change. If you see any intermittent operation or if it doesn’t reach that, you unscrew it, a little coolant starts pouring out, you get a new one with some Teflon tape and you screw it in. It costs about $20 or so. It just unplugs and unscrews. And those are the sensors that affect the operation of the car most critically.

Speed-Distance Sensor

What about the speed-distance sensors? I had an issue with one that gave me fits and I was reading one place that they said the speed-distance sensor is actually what sets the fuel MAP.

It is used in setting the air-fuel ratio in certain conditions, that’s true. The speed-distance sensor, again, is a hall effect sensor just like the one in your distributor. It’s a shutter device, and it gives out eight pulses per rotation. It’s in the transmission and the transaxle. Some of them are two-wired, some are three-wired depending on whether they have to run voltage to it. When it comes into play is when you are decelerating. As the computer takes the input from all the other sensors, it reads whether the vehicle is in motion and decides whether it has to keep the idle up a little bit longer as the car’s coasting down to a stop. And when it knows the car’s going to stop then it drops down to the regular curve idle.

If that pulse is missing, it’ll think the vehicle is stopped and it won’t hold that idle up so you can be decelerating and the idle will just plunge down to its 800 or so RPMs and that may cause it to stumble or stall out on you as it’s slowing down. It’s also used by the cruise control as input to know whether the vehicle’s moving or not. And there’s not a whole lot you can do about that but replace it. There’s no good way to test it because like I said it’s like a hall effect sensor. Unless you pull it out of the car and spin it and put it on a volt meter, you can perhaps count the pulses. But they pretty rarely go bad. It’s almost always a connector because it’s down there in the transmission and it’s covered in oil half the time and that’s usually what fouls up the signal. Occasionally one will get brittle since they’re made of hard plastic, so you may occasionally find one that’s actually fractured a little bit and you just pick the pieces out and put a new one in. They run – I haven’t bought one lately, but I’m going to say they’re probably somewhere around the $50 to $60 range maybe. I had to replace one for $35 a long, long time ago, 20 years ago. So they’re probably $50 to $60 range, maybe a little more.

It takes the place of the speedometer cable. Which is nice because speedometer cables are a real pain when you have to remove the dashboard and you have to put your gauge back in and connect it before you can pull out enough cable to get your hand in there to reach. So you typically disconnect it at the transmission and pull all that shell.

Some cars have two, an input and output speed sensor depending on how they’re setup just to make it more complicated. There’s only one on a lot of older cars. It’s funny I say older because it doesn’t seem old to me. It’s my car and daily driver.

I don’t know if an ’88 has a speed-distance sensor and it’s got the cable hose. Then later on you’ve got the same thing, but with a stub on it, and I have a cap on it on another car. Then a third car has four wires going into it or three wires going into it, and no cable and it’s just flat. And that’s what went into the…

That just shows the evolution. Because the computer was using the speed sensor even when they had a speedometer cable. They were using it for the purposes of holding the idle up and for the cruise control. And the other thing you’ll find too is there’s different ratios for the gearing on the speed sensor. The gear itself is reusable, if you disconnect it and pop it on the new sensor. And they’ve made 19, 20 and 21-tooth sensors depending on what your tire size is and your axle ratio. I’ve had to play around with that because the car I just bought, it was reading 2.5% low on the odometer but dead-on on the speedometer. So I got one with a different number of teeth and put that in and it was reading +5%. So I put the other one back in and decided it’s better.

There’s a chart in the service manual on what gear to use.

Yep, and it still gives a 2.5% error which is a little too much for this one. But if you change tire size, you want to look at possibly changing speed sensor because everything will be off. So the signal for the speed sensor goes up to the dashboard, goes up the instrument panel, and from there it goes out to the computer and from the instrument panel it goes to the gauges. So there is a circuit on the instrument panel that’s called a DAC, Digital-Analog Converter, and that’s what drives your analog gauges. It converts that signal to an analog signal which is your sweeping-dial gauge, and that will drive your speedometer.

The odometer is typically driven by a stepper motor, so the signal is still in its raw digital format and drives this little motor that turns the odometer gears. And most of us know about the prices of odometer gears. If your odometer breaks and your speedometer is still working, there’s a little 20-tooth blue gear in there that’s made of material that gets brittle over the years and one or may teeth snap off. It may act intermittently and then quit or it may just quit suddenly. There’s a website, I think he’s a sponsor so I’ll say it, odometergears.com. $25 plus $4 shipping gets you this little gear. This guy has actually made the mold for it and it’s a better plastic and more durable, and you have to use tweezers and maybe a drill and a little prying to get in and pop the new gear in, but once it’s in there you’re all set.

And one of the things, by the way, that can fracture that gear is if you reset your odometer while you’re in motion. I used to do that without thinking and it’s not a good idea because the gears are always turning, and if you hit that reset button there’s a chance you can grind them. So I always make a point of being parked at the pumps when I write down my mileage reading then punch the button before I get into motion again and it hasn’t broken yet. So with that, I think that’s about everything I had for today. If you had any questions I’ll be glad to answer them.

If you take an AIS motor and make it work outside of the car so you can retract it, or see that it’s stopped… or pull wires, see if it’s the windings maybe?

There are, to drive it in and out. And in fact the instructions tell you if the plunger is protruding more than once inch you’re supposed to retract it before it goes in so that you won’t force it into the throttle body and crank it and then damage it.

The tester, but how do you do a battery pack or…?

Yeah, they do. And I’ve looked at the schematic for it and I still have not figured out which pins to drive which polarity, but you put 12 volts and ground to a couple of pins and you should be able to retract it. But I haven’t had an occasion to try that yet. That’s something I want to experiment with.

The inner two’s one and the outer two’s another.

Pins one and four are tied together and two and three are tied together.

The middle two is like going one direction; the outer two are going the other. But which one is the plus and the minus? No, it’s actually two motors thrown together. You power one coil that runs one way, because all it is is just a stepper motor. If you put the plus one center, yeah, one and four is one coil, two and three is another.

That’s something I want to try and document, and once I figure that out I’ll put that up there. There are instructions on the Internet for just plugging in the connector in the car and turning the ignition on and driving it certainly. Yeah. There are a couple of generations of AIS motor, and the newer ones are pretty simple. It’s really just a little phalange with a plunger. The one in my 1984 turbo is this big, long cylinder. They’re very hard to find and they tend to malfunction more but people have opened them up and tinker with them and managed to get them working again. Right, yeah, and sometimes they come apart internally or something goes wrong. So I hope I never have to experiment with it, but if I ever get a spare one I’ll play around with it.

I think that’s the one you see in all the descriptions of them because I’ve never seen my ‘88 being listed. It had the little pinhole style.

Kind of like that shuttered…

Yeah, every instruction talks about the shutter.

I think the other one has six pins on it and the new one has four. I think. Like with anything else, you really want to try and figure it out before you go tinkering with it because there’s nothing worse than learning on your own and breaking it and saying now I made things worse and now I have to go out and spend the money to buy something when I could’ve fixed it myself.

On our website are all the fault codes. Most people don’t know about the key dance method where you can look up fault codes there. They’re not infallible but they’re a very good guide and probably the first thing you should do.

Coming down here this weekend, my car broke down ten miles into the trip. The engine just quit and I coasted to the side of the road, and of course the first thing I do was the key dance and I got Code 55, end of message, no fault found. And it cranked and it wouldn’t start. So by the side of the road there wasn’t a lot that I could do besides pull the distributor cap and look inside, and I found that the ignition rotor was charred and the sensor button on the distributor cap was charred. I called the tow truck, they brought the car home, I bought the new parts and put them in, made no difference. So something else is wrong.

So now we’re going to get into the diagnostics of do I have fuel pressure at the fuel rail? I’ll just crank it with the engine cold so I don’t start a fire, push the straighter pin to see if a little fuel squirts out and if there’s fuel there I know it’s working so the injectors I’m sure are still good. If not, then I’ll go looking for the spark. They make a nice little device, inline tester for spark you can plug into the boot of the spark plug wire and it has an alligator clip you can just ground to the engine and an adjustable gap.

I had an ’86 Dodge 600 and it quite on me on the side of the road, and I found out it was called the Z1 circuit. It cuts off the fuel. It cuts off the injectors and the fuel well.

Z1 is a ground.

It’s by the battery, and you get battery corrosion from the battery on that plug that’s right beside the battery and that was a simple fix, but it took me three days to find it.

Grounding is probably one of the biggest causes of trouble in the car. Intermittent operation can start right quick, and yeah, Z1 is a ground which also connects back to the alternator circuit. So yeah, there was a braided strap on these cars that runs through either fuel rail or intake manifold from the firewall, and if that breaks you will lose your fuel injection, you will lose most of your sensor grounds, and then the car will just quit right then and there and you’re stuck.

If it gets loose it’ll drive you crazy.

If it gets loose then you’ll have voltages fluttering around which will cause all kinds of strange operation. There’s a ground from the negative voltage – negative battery terminal – down to the fender well, and that provides the ground for your computer so if you lose that your computer will have floating voltages in it. And of course the ground from the battery to the block, and then there’s another sensor ground on a lot of these cars. There’s a ring-turn terminal that goes to the driver’s side block and that’s the ground for the oxygen sensor and some of the others, the throttle-position sensor. And that wire often flexes and breaks, so I’ve had to replace that.

Are there any problems with the motor mount jumper?

It’s missing on my current car. I’m going to make a new one Monday. It doesn’t cause any electrical problems. It’s there for two reasons, and one of them may be more legend than fact. One of them is it’s there to prevent electrical noise – higher frequency noise – from the spinning drive train to be transmitted through the cross-chassis. The other claim is from a galvanic corrosion issue to make sure that there’s no voltage potential difference between the axle and the engine frame. I’m not so sure of that because that just doesn’t seem like it’s a good enough connection to begin to deal with that problem. But you do want to have that connection.

Braided grounds versus regular hookup wire, the braided strap acts as a band-pass filter. It actually filters noise out up to several hundred kilohertz, so it acts almost like an RC network. That’s why you don’t run just regular wire to replace a braided strap. It filters out noise up to several thousand hertz, so if you start getting a lot of radio noise where you didn’t have any before and you replaced that ground or that strap broke, replacing it with a braided ground strap should eliminate that noise.

Let me ask you a quick question. You’ve got a braided ground strap that goes from the back of the engine to the firewall. You’ve got your connection – negative battery goes to the body, and it also connects to the engine. Why don’t the battery vibrations just travel along the wire that goes from the battery to the body?

The shortest path to your radio and to your gauges is through the firewall ground. So that’s the one that you address. That’s where you can snub it out. If you try to snub it out further away, it could get regenerated or higher frequencies can find their way through and still cause problems. So that’s why it’s used close to the source of trouble. There are kits out there – one of our members has used one, Monster Cable, and he swears by it. It’s a grounding kit.

They can work very well or they may cause problems, and people who’ve had no problems don’t like to hear that it could actually cause a problem. But you can cause a problem with too many ground connections if you start adding ground connections, and the reason is you start creating what’s called a ground loop. If you have two ground wires running to the same piece of metal, fire wall or whatever, if one is a slightly poor connection or higher resistance because it’s a thinner wire you are going to get more current conducted through one than the other one and you are going to get a slight voltage differential between the two. Now whatever gauge or device is closer to that defective ground, it could be floating a tenth of a volt above or below the true ground that you want, and if it’s enough you can get a voltage difference that can start throwing your sensors off.

So more grounds are not necessarily better. You really want to rework the factory grounds the way they were. It’s not add this in parallel because bigger can be better. So you have to be careful. If you use one of those kits, you don’t want to leave the factory one in place in parallel with it if you add a new cable. You don’t want to have a ground of a different wire diameter than the other one because you’re going to get slightly different resistance through it and you’re going to start to setup these ground loops. And as I said, depending on the magnitude of it you may never detect it and therefore people love these kits and they love the car performs better because you restored a ground that was defective with this new expensive kit. You could’ve done the same thing maybe by fixing the factory wire, the factory connection, for almost no money at all. But some people think that aftermarket has to be better than what the engineers did at the factory. Occasionally that’s right, but not often when it comes to something like that. The electrical engineers really knew what they were doing when they designed these cars.

Do you have any source for schematics for the clusters? How to repair those when they start malfunctioning?

No. I have the factory service manuals for my car and they don’t have it in there. All they have is the pin out, the connections to it, because it’s proprietary and they’re not so much worried about someone stealing their design, it just that it never occurs to them that anybody’s going to try to service their design, that we’re actually going to have this car 20 years later and open it up and rip it apart and start tampering with it yourself. I don’t know of any way to get it because chances are Chrysler probably threw them out long ago, and they’re not even in the file cabinet somewhere. It’s before the days of massive electronic storage of design, so it may have even been sketched out on vellum paper or maybe in some electronic file format that’s long obsolete and was never converted.

So chances are pretty poor of coming up with it. Trying to reverse-engineer was pretty tough too because there are a lot of custom circuits designed for the automotive industry, and the part numbers on them don’t correspond to anything you’ll find in a catalog. So you’ll look at these mystery packages and you’ll say what is this? And I’ve run into that when I’ve tried to tap out some of these circuits.

There’s a guy on a forum that’s done the radio, the laser adjustments, Jeremy Schrag. He ripped into those and that was very helpful to me this past week.

I thought that was brilliant, because you can take one that won’t play a CD at all and restore and it may work forever or it may at least work for a few more years.

But it’s hard to get into that pocket. There were independent repair agencies that used to do the electronic instrument cluster repairs, came down south and there was one up in Syracuse. I figured those guys must’ve had access to factory schematics or something along those lines.

Either that or they figured out enough of it, and they scavenged the mystery parts and they simply swap them out when they can’t identify it. But yeah, they’ve invested the time to be able to…

Somebody here has sent clusters out to a company that specializes in redoing them, and they even restore the odometer readings and they’re certified by the state to be allowed to do that. They read the mileage out of the memory in the computer before the car’s restored there and they actually recertify and restore the reading to the reworked model.

But I think the person that wrote that up paid someone $700 parts and labor, so you really want to think twice about doing it. You might not want your daily driver to have that invested in it. One other thing, quick mention of this, this doesn’t apply to a lot of cars but it’s something that caused me some grief so I thought I’d pass the word along. If you have a late 80s to early mid-90s Chrysler product and you have a tachometer, chances are it uses what we call a small plug-in card that goes on the main instrument panel. It’s the tachometer drive board, and the list price is something like $100 for this thing.

The grief that I had was my battery kept getting drawn down, and I found it was pulling 100 milliamps with the engine off, and that’s a lot. My brother owned this truck and he went through four batteries and the dealer could never figure out why. The car sat while he was off in the Navy for a while. The battery went dead and he’d throw it away because it was so dead he couldn’t charge it. And he sold it to me and he said just put a new battery in and just make sure you run it often.

So I measured this current draw and started pulling fuses until I found which circuit, and then I looked in the manual to find out what’s off that circuit that could be causing a problem. And I noticed my tachometer’s holding a reading at 1000 RPM, so I pulled that board out, brought it into work and I spent some time – not company time, lunch time of course – and I tapped out as best of the circuit as I could. There were some mystery ICs but I figured out most of the circuit, and then I found out why it was drawing 100 milliamps. And it wasn’t a defect, it was the design. It was a design flaw. This thing was allowing the current to flow from battery to ground, and for some unknown reason to me they had both the ignition power and the battery power running into this tachometer circuit. You don’t need a battery to power this thing because you don’t have any RPMs with the engine off so why is the battery running through it? And it can’t be power sequencing because they’re virtually the same voltage.

So I looked this over, and a few of you might know anything about electronics. It was a 5 volt zener that they used as a power supply for the 5 volts for the rest of the circuit. And there was a transistor above it, and they had chosen a value that kept that transistor turned on. So it was sucking the 12 volts down through this transistor with the engine off and it was pulling 100 milliamps straight to ground all the while this car was plugged in. So I cut the copper trace on the circuit board to the battery and I put a jumper wire from there over to the ignition pin, put it back in and it still works exactly the way it always worked, fixed for free, and the battery is drawing zero milliamps with the engine off and I can leave it for two months and it won’t draw the battery down. So that’s something I’ve got to publish for the site too. I’ve got some photos and a schematic I put together, and there’ll be instructions on how to fix those. Not every car shows a drawing of that much. This is my ’92 Dakota, and it’s also used in my ’92 and ’93 Daytonas. It’s probably used…

In the back of the cluster?

On the back right side of the cluster. It's in that instrument pod that the Laser and the Daytona and the LaBarons all used. It was used in the Dakota trucks of that vintage. It's probably used in a lot of other products of that vintage too. For some reason, they don’t all draw that much current. Maybe some years had the resistor value changed or the transistor wasn’t turned on, but my car only draws 35 milliamps and the truck was drawing 100. That’s a problem if you want to leave it for a month.

A difference in the production values of the actual transistor in the Zenith?

You’d think they would change the part number of the circuit board. It's the same part number. It holds the reading with the engine off.

I had two problems show up for a short period of time in cold water. One of them the tach didn’t work on a cold start and I drove three or four miles down the road and all of a sudden it just sprang to life, and I had another one where I started the car and the needle flew all the way around past the stop point and I thought I was going to have to take it apart but I shut it off and started it again and it corrected itself.

But those contacts, for some reason, I guess get off sometimes?

Yes. A couple months ago my voltmeter and my oil pressure gauge stopped working. I’d start it up and they were both reading zero on my ’93 Daytona. I was expecting a bigger problem maybe with the circuit board or something so I pulled the dash out, I took the clear plastic cover off the gauges, I pulled the gauge set out, plugged it back in and it worked. So it was just the tin oxide on the pins, the contacts. So I made sure I tightened the screws down a little more holding it in there and it’ll probably never happen again.

Replace the ignition switch yet?

No. I’ve never had an ignition switch problem at all in any car ever.

The switch assembly, I don’t know it was nine or ten pin towards the bottom, it was the clamshell housing that goes around the upper column/lower column. Have you seen this problem yet?

Oh. I’ll be taking that apart, because I saved the steering column out of my ’92 because it had cruise control and rather than try to feed the wiring through and screw around with the clock spring, I just took the whole steering column out and I’m going to be swapping it into my ’93 because I saved the cruise control servo and the wiring is under the hood. But I want to preserve the same key so I’m going to have to swap the key cylinders.

It’s a piece of cake. You have to pull the steering wheel. Actually, no you don’t. You don’t need to.

Well I’m going to swap the steering column because that’s how I get the wires for the cruise control into the current car. But I want to take the key cylinder out of the ’93 and put it into the ‘92s column and drop it in. I’m hoping the mating wiring is there for the cruise. It was under hood so I’m hoping it will be under the dash.

That’s a separate connector. It’s like a flat ribbon cable that comes through the column.

Okay, that’s what I’m going to find out is if the mating connector’s there. I want to have the cruise control on this car. I’m transferring the power locks over from the other car.

Just check that you have a nine or ten pin connector and it’s not scorched because it’s a white, plastic connector. So if it’s browned or yellowed or bland… I have a couple that are on convertibles. I’ve answered a lot of questions and stuff on this site. I have friends with half a dozen of them, and that problem showed up on more than a few.

I think I may want to look for where I can mock a relay under there. Maybe just avoid the problem altogether. Yeah, it should be pretty easy because the switch is just taking the two load wires so you just put those load wires on the relay and you just have your switch now drive the core side of the relay. Okay, any other questions?

Yeah, I got the Shadow week. My son took the ’93 Shadow, I guess the tach was working then it stopped working. So he went through and we swapped it from another car. That was working for a while, then he said it went out on him so we went back through and tapped all the solder joints and put it back in. It ran for a while. I got it back from him. It’s not working, but that’s part… no, it’s not this Shadow.

You know, all the gauges on the pods I plug into these sockets, they’re fitted pins, long pins, and they plug into these sockets. I went back and actually had to scrape the oxides and plug it back in. But it’s always a good idea to reflow the solder joints and go through. My ’84 Daytona, I’ve got problems with the backlighting. The circuit board, the copper’s tarnished enough for me to put the bulb in and rotate this. I think the wings have relaxed on their sockets where it’s not pressing in. You bend them and they just go against. I’m just going to take all the bulbs out of my newer Daytona and put them from that board into this one. If that doesn’t work then I’ll start building up the tin layout and soldering.

[Regarding LEDs], I saw one picture that looked really good. It looked like nice, even lighting. But I’ve heard a lot of them, people have just got points of light blinding back. You have to be careful how you do it, but that’s probably the way to go if you’re having problems. I haven’t had any problems, pod-type for the back lighting so… and the bulbs almost never wore out so to me it’s not worth it.

I was just thinking more like if you’ve got a problem where you get pulls…

If it’s chronic I would change it, yeah.

You’ve got a bulb that every now and then, it’s just hard to get to, and you figure you’ve got a lifespan on an LED of like infinity.

From Daniel Stern:

LED signalling lamps (brake, tail, turn...) are not a “retrofit” item in the sense of dropping in an “LED bulb.” The “LED bulbs” that are available all over the Internet are dangerous junk. The brake, tail, parking, and signal lamps of your car rely on a point source of light (glowing filament) that radiates more or less equally in all directions -- a sphere of light -- collecting and distributing that light with optics in the lens and/or reflector. An LED is a vastly different kind of light source... it projects a very narrow beam of light in one direction. There's no way you can get enough light through a wide enough angle (horizontally and vertically) to create a safe and legally-compliant lamp. This applies even to the “LED bulbs” that have both side-facing and rear-facing emitters. The problem is not with any particular implementation, the problem is with the concept, which cannot work.

Not only is it crucial that the intensity be within the proper limits through the relevant range of angles to provide a penetrating signal to observers at any angle, not only must the ratio between bright and dim modes be correct (for combination lamps), but the luminous lens area must not be reduced. With “LED bulbs” in lamps meant for filament bulbs, you tend to get a little dot of light with the rest of the lens almost completely unlit. Not only is the visibly lit area dimmer, it's also smaller.

You can sometimes place ready-made truck/bus LED lamps inside the lenses of your car's original lights. You have to be careful to get the placement right; they need to be upright, facing straight, without any slant, tilt, or inward or outward rotation (except for units made for postal trucks with a 7° forward tilt to the rear surface where the taillamps are mounted). If the units you pick have a "TOP" marking, it must be at the top.

I learned, anyone see the taillights in the Laser and Daytona? They were a pain to take out, and you have to take them out completely to change a bulb. There’s ten bulbs in them, and the guy turned me away when one instrument marker bulb was out on one corner. It takes about 20 to 30 minutes to open up depending on how cold it is outside, then your finger’s freezing up on you. But you have to basically open the hatch, take out all those plastic buttons, take that panel off, take out about nine either Allen or probably actually torque screws. They’re usually frozen and rusted in badly. You’re going to have to cut one, and then you pull the whole assembly out. So I learned that. If one of them is out, I spend $25 and I change out all of them at once and I feel to see if any sockets are loose and I’ll replace a socket if a bulb doesn’t feel tight then I won’t have to worry about it for a long time.

I do that when I do instrument clusters and we need to pull the cluster out.

Now when you put LEDs in for things like turn-signal bulbs you’ve got to be careful because they have a much lighter inductive load. A regular incandescent light bulb has a high-resistance winding, and it’s a fairly long filament so it acts like an inductor which is a voltage storage device. And they’ve designed your flasher to work with that load to flash at a certain rate. You put an LED in you’ve got a much lighter load and now the thing flashes faster than even I can see practically so you’d have to compensate for that by putting some kind of inductive load which would be a coil of wire. A resistive element can work to some extent if you put a wire around a resistor, but you have to do a compensation technique to get it to flash the same. Some of these, yeah, if it’s one that’s not made to run the original load yeah. But it’s not just a one for one swap to put the LED in there. [There are other problems with LEDs for exterior lights, especially brakes and turn signals — see our article.]

Probably nice and quiet to the ear.

Not that I know of, no. Because you can hear it because what you’re hearing is the armature.

You can barely hear it in the car when you’re driving.

My ’84 Daytona it’s almost silent. It’s very hard to hear. My ’92… I have to look at the indicator on that car just to tell if it’s flashing. By the way, common problem with the pod dash. I’ve had several problems now, and the current one is that it doesn’t always cancel itself. I’ve had problems where it just fails to work part of the time, it just doesn’t turn on, and it seems to have gotten past that somehow. It’s healed itself. But now about half the time it doesn’t cancel and I have to manually cancel it. So if anybody discovers that, figures it out before I do, post it up there. That’s a mechanical issue though because you’ve got that plastic arm around the steering column.

Yeah, I got what I thought was the correct one but it was the difference between 6667 I guess and I tried to trim off some of the tabs, but not enough. It’s no big deal to manually…

See these cars, we have the turn signal in the instrument panel on the dash and there’s somehow, it’s probably an electromagnetic control on the steering column, but it cancels this thing and I haven’t quite figured out how it does that. But it’s going bad. It seems more often on hot days it’s a problem, so if I’ve got the air conditioner blasting it seems to heal itself eventually. So again, it could be a solder joint opening up as it gets hot and expands, so first thing I’m going to do when I get home is pull that pod out and reflow all the solder joints and check all those wires. And if the problem goes away, that’s it.

It could be inside the switch itself, in which case there’s no way that’s going to get fixed. I had a spare pod and I gave it to another club member so he could fix his car, so no good deed goes unpunished. Yeah, it’s got to be something but it’s not always tripping. My first suspect would be a bad solder joint or wiring. When it fails, both directions fail. It’ll flash, it just won’t cancel. Occasionally in the past it’s failed to flash when I turned it on and then it healed itself, and I’m always afraid that’s going to happen at inspection time. So I try to get it inspected in cooler weather. You can find a Bosch around junkyards, people selling them.

Not new?

Not new, I don’t think you’ll find it at a dealership at this point. It’s almost 20 years old. But that switch, I looked at it and it’s not mounted very well inside that pod. The wires are really stretched tightly. You know, half an inch of wire would’ve made a big difference so I’ll be reworking it and I’ll post the results if I fix it. Or if I don’t fix it.

If we get enough of a database of all these problems and all these solutions, you could do what AutoZone is doing and charge for access. When it gets up to retirement age and you want to figure out how to get a steady income, start selling a subscription to this. Well, a small little bit. Or a one-time fee. That’s assuming I have a car that runs of that vintage at that point.

Rust is the silent killer. That’s what’s getting these cars more than anything. I lost my last car to rust or I’d still be driving it today. It ran like brand new, 308,000 miles and the original engine. The clutch had gone 270,000 miles before that actually exploded, and it was all original claw joints, high-rods, axles, CB, everything. All that stuff was original, the springs… I did replace the shocks only to see if I could get a better ride. That was it for repairs. The rest was just little stuff like a water leak here or a switch there. Once it starts getting unsafe to drive, I’ve got a family to think of. I saved all the parts I could, so the parts are going to live on in this car.

There you go. That’s what I did with my first. When that one rolled to a stop, I took out what I needed and it rolled away and the next one...

I was lucky with the ’92 and ’93, almost everything’s identical. Everything. I’ve got the whole drive frame in reserve for when this one wears out. My first new car was straight out of college, an ’85 Daytona base model.

I went into a dealer and I saw this little ’85 five-speed, good little car. And he wouldn’t get a job to afford insurance so I just kept it. That’s a nice car.

I got this car thanks to a college kid. I was looking for a place in Daytona and came up on Craigslist so I go up and look at it and it’s got some pretty moderate rocker rust but I know a place that can fix this now and deal with the whole thing and get it done right away. So the guy said “Yeah, we bought this as a surprise for my son graduating college. We lead him out to it, here you go, surprise, here’s your car. And he said oh wow, great and he hopped in. Oh, it’s a stick. I don’t know how to drive a stick. I can’t do this, I don’t want to learn.” So they sold it to me and they bought him a Subaru Outback with an automatic.

...

I was going home down some back roads from work one day and I came to an intersection, I’m going 25 and it’s got a green light, and just as I’m in the intersection I realized that it had a very high crown for the road that crossed it. And before I could slow down – and I heard this scrape in the road, and I left a groove in the road from the oil pan. It put a dent, a crease, right at the drain plug. I drove on and I pulled over there and I looked, it looked okay, and I go home and I could see a little bit of a dripping and I thought I’ve got two choices. I could either degrease it thoroughly and put some JB Weld on which might not stick if I don’t degrease it well enough, or get another oil pan. I’m keeping the car so I’ll get another oil pan. So I went to AutoZone, and this is so easy theoretically.

Buy an oil pan. Brand new, $80. It looks fine. It’s painted. It’s got thick, drippy paint lines on it but it works. So I get it home and get the car up on ramps. This should be easy. I unbolt all the rounds, pull the pan down. It hangs up a little on the dust shield for the transmission but I get it down and I get the one piece gasket from Velcro with the clips that go up there. This couldn’t be better. And I wrestle it up into place, start putting all the bolts in, fill it up with oil and I start the car and gush, gush, gush. It’s pouring out by the dust shield because it caught the gasket on the lip of that dust shield when I was folding it back up into place and pushed the gasket out of the way.

It did it three times and I couldn’t get the dust shield out. I tried unbolting and I snapped an 18mm socket apart. It was on so tight I couldn’t get it. I tried cutting the dust shield with a Dremel tool so that I could just get the lip over and I still couldn’t get enough clearance and I was afraid to cut more, so at that point I called up my favorite mechanic and said bring your tow truck out here and let’s tow the car in. Here’s the oil pan. He charged me $110 for the tow and the repair.

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