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Discussion Starter #21
ok I cleaned the battery posts and checked the voltage. Everything was in spec. I just changed the hep so hopefully that was the problem. I will know for sure if I dont get any problems in the next week. I will keep everyone updated. Thanks for everyones help so far. Mike
 

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Something you may want to consider before you condemn the HEP:
The HEP is the sensor that allows the ECU to determine if the engine is rotating, and, if it is, where it is in the cycle. Since the ECU switches the coil primary, it essentially sets the base ignition time. There are other factors that can change timing, but if the computer thinks the engine is not rotating, there is no ignition to time. I would get a spark tester (a good diagnostic tool to have anyways, and especially considering they're about ten bucks, last I checked) and connect it between the coil secondary and the distributor (the center wire on the cap). Then, replicate the no-start condition or stall in a safe place like your driveway, and connect the tester when the car refuses to start. No spark means either a blown HEP or a bad coil. You can rule out the coil with a simple 12V light across the coil primary leads (the wires going to the coil from the computer). It should flash when the engine is cranked-- no flashing indicates that the engine is either "not rotating" or there is a break somewhere in the wiring between the computer and the coil. It's very likely the Hall, but a couple of quick checks with some pretty cheap equipment can keep you from spending $35-40 on a new part your car does not need.
 

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Discussion Starter #23
Heres the thing. I would love to do that but the car does it so intermittenly I cant replicate it. It can go over a week before it happens or stalls when Im at a light. It never seems to do it when im at home with my tools. Go figure. I already bought a new hep from the parts store for 20 bucks(using online coupon codes saved me almost 50 percent) so time will tell if that was my problem or not. I would like to still check the coil if possible though. What kind of 12v light do I need to test that?
 

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Discussion Starter #24
OK, so more bad news. I replaced the hep sensor on wednesday but I didnt drive the car all day. It started up fine and everything. Now yesterday, Im leaving for work, everything is fine. Car is running great. 20 mins into my commute, the car loses all power. Im flooring it and it slowing down. Then the car dies. Luckily I was able to pull over safely but I did have to get the car towed. At first I was thinking the worst, fuel pump. The car was cranking perfectly normal as usual but this time was not turning over at all. So I get the car home and go to work. When I get home I figured I would take the new hep back out and put the old one in since I figured that wasnt the problem and get my money back. Well what do you know, I install the old hep and the car starts right up! What are the odds of getting a bad brand new hep sensor? Should I still go and return the hep and buy another one? Maybe just a bad new unit. Could it possibly be the coil? Im still not getting any trouble codes at all now. What is the easiest way to test the coil?
 

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Coils can be intermittent as can many other electrical components and wiring. A bad HEP out of the box is possible, but really very unlikely. Is it an OEM part?
If the symptoms have changed, this may be a different issue?
Have you tried a 'wiggle' test by slightly disturbing connectors and harnesses? Sometimes a reaction at a certain spot will locate a break or intermittent connection. If you can 'make' it happen, you are almost there.
Is it affected at all by hot/cold, wet/dry, type of driving, etc? Without fault codes that point to a particular area, sometimes good old-fashioned detective work comes in. The more that you can find out, the closer you'll get to your answer. Fuel pressure gauge under a wiper and the 12 volt pulses on the (-) negative side of the coil can be monitored from the driver's seat while driving until it quits if you aren't sure about spark or fuel being the problem/
Usually a loss of spark is immediate and loss of fuel pressure is more gradual. If the fuel injector quits, that can be fairly immediate and can happen if the PCM loses the HEP signal. Without sensing engine rotation, the PCM will lift the ASD (automatic shutdown) relay to shutdown spark and fuel.
 

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Not at all unusual to get a bad HEP out of the box especially if you got it from Autozone or Advance. I used to work for both and found their electrical ignition parts to generally be very poor quality. You really need to take a close look at the plug on the harness where the HEP connects. I had one that I actually ended up using a wire tie on in order to get it to stay tightly connected. That was on an 87 Horizon I had years ago.
 

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Most likely, then, neither HEP is bad, but there is an intermittent connection in the harness to/from it. The HEP plug is notorious for not fitting well and for getting crap in it, as chuzz said. The other very important place to look is at the connectors to the PCM. For vehicles this old, the contacts are an issue - dirt, corrosion, stress cracking.
 

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04mazdaspeed said:
Hey everyone, I have a 91 plymouth sundance 2.5 with around 110k on it. For the past 2 months now, I have been getting this very random and very intermittent stalling problem with the car. If it happens, its usually while Im waiting at a light. The second my foot touches the gas pedal the car dies like i turned the key. It has started up not not for usually about 45 seconds of cranking with 5 sec breaks to cool the starter. Now this doesnt happen all the time. It seems to just do it when it wants to. Now while Im driving there are no problems at all. Once while I was driving it kind of jerked on me like the motor stalled while driving but it happened in a split second and everything was fine since. Also, every one in a blue moon, if I drove to the store and the car sat for a few hours and come back out, it wont start. That has happened to me twice now. It took about 2 mins of cranking to get it to catch and when it does it runs fine for a while. Im at a loss as to what it could be. From what I have been reading online it could possible be the speed sensor and/or the distributor(hep?). Any and all help would be greatly appreciated. Also if anyone knows where the speed sensor is located at on the car since my haynes manual doesnt say where its located. Thanks so much. Mike
There are a few things in your post that lead me to think that it could be the fuel pump, especially the random "jerk" you feel when driving (assuming you are not going over bumps, turning, or changing the speed significantly or it is raining). If this 1991 vehicle has never had the fuel pump replaced, it is probably due.

The fuel pump has a DC magnetic drive motor with carbon brushes in it and they do eventually wear out. You will never get a code when it goes out. It can fail completely and immediately, or it can fail by occasionally cutting out. Every time the car stops and you crank it, power is applied to the pump (assuming the engine turns over). In a failing intermittant pump, sometimes the brushes make up and the pump starts, and sometimes it doesn't. It acts similar to an alternator with worn out brushes (sometimes charges and sometimes it doesn't charge).

There are some tests that advanced level automotive electrical shops can do to check your fuel pump, but it is a time consuming process. It is also possible to tee in a fuel pressure gauge, even to the point of driving with the gauge visible (i.e. clipped under the wiper blade and visible through the windshield). These are a bit of a PITA to set up on a Chrysler 4 cylinder TBI car with no gauge port.

My gut feeling is that your pump is going bad (assuming original 22-23 year old pump).
 

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ImperialCrown said:
There is a 'quick connector' fuel line tee: MP10005997722_P255045_500X500.jpg
You may be able to assemble a tee with 5/16" EFI hose and an adapter: Gauge+Fuel+Pressure+Test+Kit.jpg
Tuck the gauge underneath a wiper blade (if it doesn't look like rain) and drive it until stall.
I like that first one.... that must be a Chrysler special service tool. I use a cheaper version of the 2nd one. I think it is a Harbor Freight tool and I never really feel comfortable driving with it connected. There are 6 hose clamps involved in setting it up and if not careful, 1 more more can spray if not totally secured. The unit uses a barbed tee, 3 sections of 5/16" EFI hose, and a 0-100 PSI gauge. It takes a while to set it up too.
 

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Discussion Starter #31
That random "jerk" I had only happened that one time. It hasnt happened since. I did have the car die out on me one time when I was turning left from a stop sign though. The reason I believe that I got a bad new hep was that I was trying to start the car for hours before I called a tow truck. Took the car to a shop then went to work. After I went to go try starting it again to no avail still. Then as soon as I swapped the old hep back in, it fired on the first turn over. I then proceeded to drive the car 20 miles to my home and the car didnt show one problem at all. Nothing. Also if my fuel pump was starting to go, wouldnt it affect the car even while im cruising? If im driving on the highway or just steadily driving without stopping the car displays no symptoms at all. Floor the gas and the car pulls smoothly up to redline. I will look into how im going to get a fp gauge on the car. That will atleast tell me how the pressure is.
 

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Discussion Starter #32
Also I have said before that I havent changed the fuel filter when I did the tune up 5k miles ago. Not sure if its ever been changed. That is next on my list to change since a clogged filter could also give me my symptoms I believe.
 

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04mazdaspeed said:
That random "jerk" I had only happened that one time. It hasnt happened since. I did have the car die out on me one time when I was turning left from a stop sign though. The reason I believe that I got a bad new hep was that I was trying to start the car for hours before I called a tow truck. Took the car to a shop then went to work. After I went to go try starting it again to no avail still. Then as soon as I swapped the old hep back in, it fired on the first turn over. I then proceeded to drive the car 20 miles to my home and the car didnt show one problem at all. Nothing. Also if my fuel pump was starting to go, wouldnt it affect the car even while im cruising? If im driving on the highway or just steadily driving without stopping the car displays no symptoms at all. Floor the gas and the car pulls smoothly up to redline. I will look into how im going to get a fp gauge on the car. That will atleast tell me how the pressure is.
The next time you get into a situation when it won't start, try banging on the fuel tank. If it starts then you have the answer.
Definitely change that old filter, although I would think that a clogged filter would not cause a situation that would be so intermittant.
 

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04mazdaspeed said:
What kind of 12v light do I need to test that?
Any old 12V lightbulb will do. What this is looking for is ECU firing signal to the coil, and really won't give any indication of what's happening on the secondary side. That's 30+ kV, so don't connect any sort of light to that.
 

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B10alia said:
Any old 12V lightbulb will do. What this is looking for is ECU firing signal to the coil, and really won't give any indication of what's happening on the secondary side. That's 30+ kV, so don't connect any sort of light to that.
I like to use an inductive pickup timing light for those situations. With a helper cranking (or with a remote starter switch), you can view nice steady flashes from your timing light (or not).
 

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Discussion Starter #36
I will definetely remember to try that next time but would I just be better off just replacing the pump now anyways? I hate to just throw parts at the car but for what the pump costs, it would pay for itself if I dont have to have the car towed again.
 

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Parts and labor to have a pump replaced will be $400 to $650. If you do it yourself, you're still looking at $200-$250 by the time all is said and done. So it's more of a peace of mind situation for you to replace it proactively (as I'm about to do with my truck). But best to fix this issue first, before touching another system in the car and potentially complicating the diagnosis and repair.

You can test the HEP by powering up the 8V and ground connections, and monitoring the output with a voltmeter. It should switch back and forth between 8V and ground when you pass a metal plate through the sensor.
 

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04mazdaspeed said:
I will definetely remember to try that next time but would I just be better off just replacing the pump now anyways? I hate to just throw parts at the car but for what the pump costs, it would pay for itself if I dont have to have the car towed again.
I can understand the costs for towing... plus it is miserable waiting for a tow truck, and unsafe if your car dies out in traffic. I got a AAA membership to cover the tow costs, and when all 3 of my sons were driving, it more than paid for itself.

Changing the pump is a gamble and there are no guarantees that replacing it will fix the current problem. An ancient pump should be replaced, especially if you plan on keeping the car. That goes for the timing belt too (not your current problem). A failure of either of those can leave you stranded with no warning. After the pump went out on my wife's 91 Sundance many years ago when she was 30 miles from home, I proactively changed the pump in my 91 Spirit. I didn't want to get caught in a similar situation. These can be a nuisance to change, especially if there is rust on the strap studs. With a running pump, you can discharge most of the remaining gas that's in the tank into 5 gallon gas cans by rigging a tempory length of fuel line to the return line.

Obviously we would all like you to be able to diagnose the problem, make the repair, and be confident in your cars reliability.
If you have an inductive timing light, try looking at the flashes from the coil secondary and the plug wires (see previous post). That could give you a clue to a healthy ignition system.
 

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The HEP pickup or it's mating connector and associated wiring may still be an issue. Did you vigorously shake the HEP lead out wires, connector plug and plug lead out wiring while the engine is idling ? If there's a break a good wire jiggle will usually either hiccup the engine or kill it outright. Also check your battery to head ground connection and back of head to firewall ground strap ( braided ) if you have one. Do the same at the tps plug and wiring and the MAP plug and wiring.
 
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