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Discussion Starter #1
Hey everybody,

In the morning the past few days, I get a check engine light and my voltage gauge jumps around a little bit. I mentioned the morning because by the time I am able to work on the car (late afternoon/evening), it behaves the way it should. My thoughts are that the dew/moisture in the morning air is causing an intermittent connection issue, has anybody had this happen before?

I have a lifetime alternator so no worries about replacing it, but what else should I be looking at before going through the work replacing it? I have already cleaned the battery terminals, and while the problem was gone the next day, it returned again this morning.
 

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It's probably the alternator, but check for loose connections on the back of the alternator. Make sure the ground nut is secure. If it is a chain store sold remanufactured unit, I would suspect even more that it is a bad alternator. I ended up going through a couple of units for a remanufactured POC I got at AutoZone for my Dodge.

There is a very slight chance it could be the engine computer or dirty connections at the computer plug since the voltage regulator is inside the engine computer control computer. I'm betting on a faulty alternator.
 

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Whether it is tha alternator or not, do check wiring connections. I had mine jump around on my Dakota and needless to say, it caught fire. I only had the Dakota two weeks and the second time I drove it, she caught fire. Not a pretty sight, the hood still has the burn mark. Luckily I bought the truck for the body anyway.
 

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I had this recently, it turned out to be intermittent field terminal connections, either inside the alternator, or the surface rust on the nuts and studs. Had to get a new alternator because the studs broke off when disconnecting them.

But also check for a loose/slipping drive belt.
 

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I was going to suggest the same thing as Bob, either a problem with the field windings or a contact problem at the terminals. Here's why:
The alternator's job is to constantly feed current to the battery so that the battery voltage remains more or less constant. As the battery supplies current, its voltage drops, but the alternator is "filling" it back up. If you think about the battery as a bucket with a hole in the side near the bottom of it, you can see that water flowing out at some rate (analogous to current) will reduce the pressure of any water coming out afterwards (analogous to voltage), as there will be less water in the bucket to push the water out. Now, if you take a hose and put it in the bucket so that the flow going in is roughly equal to the flow coming out, the pressure will stay more or less the same. That hose is the alternator. Going back to the analogy, you can also see that you'll need some valve to control how much water (current) comes out of the hose so that the bucket doesn't overflow. That valve is the alternator field windings. By controlling how much current goes through the windings, the ECU can control the output current of the alternator. That's all fair and good until you consider that in some cases, you may only need a little current to keep the battery full, while under others, you'll need a lot. The alternator windings are split into two portions that the computer can switch on and off as needed. If there's a high demand, both windings will be "excited" (a "full-fielded" state), while if the demand is low, only one may be active, and even then not at full current.
If one of the windings can't activate because of a bad connection, or if neither of them are getting the full current because of a high-resistance connection, you'll get low current output and the battery voltage will fluctuate. Idle is a particularly bad time for an alternator, since it's not really spinning fast enough to produce much current unless it's full-fielded or close to it. If the battery has seen a high drain, like it does after starting, it will need all the current the alternator can supply. As you drive, RPM increases and the current output rises, so the battery can recharge even with the lower current in the field windings. Current demand also drops, so eventually the battery recharges and voltage stabilizes.
I always like to know a little bit about what's going on when I'm working on a problem, I find it helps me to tackle it easier. Hope this explanation helps.
 

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Discussion Starter #6
Okay, so I had some time to play with this today. Unfortunately, it was behaving pretty well while I did so. I took all of the wires off of the alternator and cleaned the connectors, and checked the resistance between the big wire and the positive wire on the battery. The number was very low, almost 0. I still have some strange behavior, though:

With the car just idleing, no accessories running, voltage at battery as ~13.9 volts. The voltage gauge sits at the first line to the right of the middle of the gauge. On the alternator, the big wire that goes to the battery is at 13.9-14 volts. On other connector on the alternator, the top small one is at 13.9 volts, and the bottom one is at 10 volts.

With the car idleing and Rear Defrost, headlights, and full a/c fan, the battery voltage is ~13.8. The voltage gauge, however, is now sitting at the first line to the left of the middle. On the alternator, the big wire that goes to the battery is at 13.8 volts. On other connector on the alternator, the top small one is at 13.8 volts, and the bottom one is at 5-6 volts.

Does this make sense to anybody, that the battery voltage is the same but the voltage gauge in the car is different? I have to charge up my drill to remove the screws to remove the kick panel to get to the computer, so I was not able to check those connections yet.
 

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The gauges aren't always trustworthy. I did a tach cluster swap in my Spirit, and the new voltmeter is much more sensitive than the old one.
Alternators are designed to put out more or less constant voltage-- the 13.9-14 is normal. It also seems like the computer is fielding the alternator correctly. The question is, are the field coils actually working properly? If you can get a hold of an induction ammeter (needs to be able to handle at least 100A), that would be the best test of whether or not the alternator is actually producing the current it's supposed to be.
 

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Rezachi said:
I have to charge up my drill to remove the screws to remove the kick panel to get to the computer, so I was not able to check those connections yet.
Nope. The voltage regulator circuitry is in the PCM underhood, not the body control computer behind the passenger kickpad.
 

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Discussion Starter #9
Ok, I think I narrowed this down, what do you all think?

At fuse 15 (for the cigarette lighter), when I remove the fuse and check the voltage across the two terminals, I have 13.8 with everything off and 12.8 with lights and rear defog on. As a test, I clamped a wire to the negative terminal of the battery, draped it up near the fuse box, and checked the voltage of the live side of the fuse using my wire as the ground. 13.8 with lights and rear defog running, and I could see the voltage change when I moved the negative probe from my wire to the other fuse terminal. What do you all think, bad ground at the instrument panel?

Of course, I again do not have my drill and the screws are stripped for the left trim panel, so I am again waiting, and hence posting about my thoughts.
 

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When you measure as you did with the last technique, there is no load, no accessory in the circuit other than the voltmeter. When you remove a fuse and substitute a voltmeter for it, any load that's active on that fuse's circuit is pulling current through the 1 megohm or so resistor in the voltmeter, and is causing a voltage drop. So it's really not a valid test.

In a car this old, you're facing what I have to do with my 84 Daytona: Undo all major electrical connections such as battery, computers, sensors, instrument panel, all ground wires, and clean them well, and reinstall with dielectric grease.
 

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Discussion Starter #11
Okay, I am 100% sure that it is a grounding problem now. As an experiment, I ran a 10 gauge wire from the negative terminal to the battery to the pivot bolt under the dash. I attached it there with a vice grip and guess what. Perfect voltage everywhere. Full fan, headlights, and rear defog and still 13.8 volts at the cigarette lighter. I also checked the voltage at the left headlight and had 13.8. As soon as I removed this wire, I was back to right around 12 volts at the cigarette lighter, and 11 volts at the headlight (no wonder they always seemed so dim). At this point, I thought of securing the nicely and leaving it, or doing the old car audio trick of running a piece of 4 or 0 gauge wire from the negative terminal to a body ground, but decided I wanted to actually fix this properly.

So, I started tearing by unplugging and checking every plug I could find, but everything looked clean. I took apart and cleaned up the grounds I could find. I cleaned/sanded the ground behind the battery tray, the ground strap from the engine to the firewall, and the big ground wire from the negative terminal to the engine. With a multitester, I am now at ~1ohm of resistance between the negative battery wire and any of those points, and about the same between the negative wire and the shock tower bolts. I then tore apart the interior to get to the ground under the left side trim panel. This was completely covered in corrosion and the area around it was rusting away, so I cleaned it up as good as I could, sanded the paint around the pivot bolt for the dash, and attached the ground to that bolt. However, I think there is another ground somewhere that needs to be cleaned.

I'm now at 12.6 volts at the headlight and at the cigarette lighter with fan, headlights, and rear defog running, so it is better, but still not the best. Can anybody think of another ground somewhere that I should clean? Or is the big wire to another body ground the best idea?
 

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Discussion Starter #12
And another update... I think the grounding problem and the alternator problem are two seperate things.

This morning, voltage gauge dropped very low. I checked the voltage at the battery and was at ~12 volts. On the alternator, i was at 12 volts at the output, 12 volts at the top screw of the connector, and 0 volts at the bottom screw of the connector. Is this the regulator not sending voltage to the alternator?
 

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Bob Lincoln said:
Okay, so I read the link and I think I get this. Current travels in through the top terminal (blue wire on diagram) of the connector and out through the bottom terminal (dark green wire) to the computer, and the computer reads the voltage off of this wire to know the output voltage of the alternator?

0 volts here indicates that at the time there is no current making it through the alternator, and snce there is current going in to the alternator at the blue wire, we know that the short is somewhere inside, unobtainable to us mere mortals, correct?

My original theory was that the bottom wire was how the computer sent current to the alternator to control the output, so now here is the bonus question. Since it now appears that the top wire at the connector is battery voltage and the bottom is how the computer senses output, how does the system actually regulate the voltage coming out of the alternator?
 

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It's all in the Factory Service Manual, how the field terminal winding works. I'd have to consult it. If I get a chance, I'll paraphrase the diagnostic process from it.
 

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Okay, so I read the link and I think I get this. Current travels in through the top terminal (blue wire on diagram) of the connector and out through the bottom terminal (dark green wire) to the computer, and the computer reads the voltage off of this wire to know the output voltage of the alternator?

0 volts here indicates that at the time there is no current making it through the alternator, and snce there is current going in to the alternator at the blue wire, we know that the short is somewhere inside, unobtainable to us mere mortals, correct?

My original theory was that the bottom wire was how the computer sent current to the alternator to control the output, so now here is the bonus question. Since it now appears that the top wire at the connector is battery voltage and the bottom is how the computer senses output, how does the system actually regulate the voltage coming out of the alternator?
The ECU has a voltage regulator that pulse modulates the field return wire to ground (rapid contact closures to the ground). If you had an external electric regulator, it would work the same way.
 

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Discussion Starter #17
This thread will not die!!!!!

I was eventually able to convince autozone that my alternator did in fact die even though it is 18 months old. I have the replacement installed, so I think i am good with the code 41.

However, I am now at a loss about what to do about the voltage dropping when the headlights are on. After installing the new alternator, I did a check at the headlights and found 11.3 volts, even though the voltage at the battery is 14.0. Here is where it gets weird. I took my same piece of wire I have been testing with and touiched the negative terminal and the body ground (right behind the battery), and after a few sparks, I saw that I had just under 13 volts at the headlight (and the wire got hot after a few seconds). Removing the wire, the voltage dropped right back down. I touched the wire from the negative terminal to the engine ground and did not get sparks or heat, so I am assuming that there is no ground issue there that would make the electircity want to flow down my wire, leaving the body ground itself as my issue. So I removed the battery box and recleaned/sanded the terminals and sanded the area that the connector touches to shiny bare metal (actually shiny, not the grey undercoat that is present under the paint). But the problem is not fixed. It is almost like the wire itself is bad. It has ~1 ohm of resistance and looked to be in good shape, but I can't think of what else it could be.

Any ideas?
 

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How exactly are you measuring the 11.3 volts at the headlight? Did you unplug the bulb and measure across the connector with the light switch on? Did you then measure from the negative contact of the headlight switch to the engine ground, to see what the voltage drop is? If not, please do so. Don't connect any more ground wires which may damage something, until we work through a proper diagnosis.

You should NOT have seen sparks or experienced a hot wire. You probably grounded the positive wire from the headlight. Let's find out what's still wrong.
 

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Discussion Starter #19
Just to clarify, the sparks/hot wire occured when I touched a piece of wire (10/12 gauge wire) from the negative battery terminal to the spot where the battery grounds to the body(right behind the battery tray). I also observed the same thing when I touched the wire to one of the shock tower bolts (I wanted another body ground to test). I thought initially that it meant that my negative to body connection was insufficient, but you just made me think that maybe it means that something that grounds to the body is drawing way more power than the stock negative to body wire can handle, especially since I do not get the same thing when I connect negative to engine ground. I will have to experiment a little more to see if the same thing happens when the lights are off.

The voltage was checked at the light socket with the bulbs installed and the headlights on. I back-probed the black and the low beam wire to take the measurement. Both headlights had about the same voltage.
 

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Measure the voltage from the negative contact of the headlight to the engine block with headlights on. Should be zero.
 
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