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This is actually for a 2001 Dodge Intrepid with a 2.7, but, i thought i would post this here because this issue seems applicable to any newer ECM or PCM controlled vehicle, car or truck. The issue i am having is, i recently changed the engine in a 2001 Intrepid, that has been sitting for a few years, and after it was running, it would inconsistently burn the coil on cylinder #4. The reason i say inconsistently, is due to the length of time before it would do it. Sometimes it would be 5 minutes, other times 30 minutes, other times, right after i start the car. I checked the wires at the plug, using a volt meter with an audible tone, and, if the harness is plugged into the PCM, then i get continuity between the 2 wires at the plug for the coil, but, if the harness is unplugged from the PCM, then there is no connection between the two wires in the connector for the coil. That says to me that the issue is within the PCM, however, others have said that that is not the correct way to test for a bad PCM, but noone seems to know how to test correctly for a bad PCM, or, at least, they wont tell me, they just keep saying i am testing it wrong. If i test the connector for any other coil, with or without the PCM plugged into the harness, none of the other coils have continuity, only cylinder #4. My question then is, is there anything else that could cause this issue, since it only happens when the PCM is plugged in, and doesn't happen when the PCM is unplugged. Also, the problem happens with or without the battery connected. Any help you guys can give me would be greatly appreciated.

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biggman100...Have you checked the ohms resistance to ground for each of the coil wires at plug #4?  Did you change the spark plug?  Is there continuity between the plug lead end and ground?  Could be a short, even within the spark plug, or possibly between the wire leads and ground.

If you can borrow or have a commercial test probe tool like a Fluke, try running an insulation resistance test between each of the wires and a continuity test between each wire and ground (shorts).  Disconnect the PCM for these tests.  The idea is to isolate the wires and test them for shorts to ground or between each other somewhere in the wiring circuit to the PCM.

Moses

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Moses, all the spark plugs are new. As for continuity between the wires and ground, the only time it gets continuity to ground is when the harness is plugged into the PCM. When it is unplugged from the PCM, there is no continuity to ground, anywhere in the harness. That is why i am pretty sure the PCM is bad, because it only gets continuity to ground when the PCM is plugged in, and only on the #4 coil.

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Good deduction, biggman100.  If the system is COP, the PCM serves as the "distributor" or trigger for firing each coil.  With a conventional distributor, spark would come from a common coil then distributes spark via the cap and rotor.   Either the PCM has a circuit for each coil/plug or a common sequential firing order signal.  (Is there an additional module somewhere in the system?) 

A quick check would be a factory wiring diagram to confirm whether the PCM or a separate ignition module triggers the individual coils.  Where is the timed trigger to fire each coil?

Moses

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Moses, after extensive research, i have learned that virtually every engine function, from fuel timing for the injectors, to when the coils fire (it is a COP system), to almost every other function you can think of, is controlled by the PCM. The PCM uses reference from the cam and crank sensors to tell the injectors when to open, and the coils when to fire. We tried an experiment with it, due to the cost involved, and assurances from a dealer that it wouldnt harm anything, and found a used PCM from a salvage yard, and the car ran like it should, although the MIL was on due to mismatch of odometer and vin, but, the dealer said that would happen. Afterwards, we ordered a PCM from a place out of florida, received it saturday, installed it, only to find that that PCM has issues. It is a reman, so, now i get to deal with them about getting a new one. As a side note, i have since learned that Chrysler cars from those years are known to have PCM issues, so this should make things interesting. I also learned, you cant get a new PCM for this car, only reman, and the place we got it from was recommended by the local dealer. As always, thank you for your help in solving this.

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biggman100...Good research and testing.  There are firms that will rebuild your original PCM.  It might pay to try one.  For ABS modules, I've had good luck with ModuleMaster at Moscow, Idaho.  (See the website.)  Others may have suggestions about PCM reconditioning.  

Mopar does have a Reman program, this is how they supply these parts to the dealers.  Here are the two pages of Mopar Reman part numbers for 2000-2001 that cover your LH model 2.7L Dodge Intrepid.  You'll need to narrow down the vehicle's options and application, your local Mopar dealership should have access to these parts:

2001 Dodge SBECIII Controllers.pdf

Moses

 

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Moses, the 3 local dealers here all said to just get a reman PCM from this place in florida, since it is a Chrysler authorized rebuilder. It seems that, since the 1999 to 2005 LH bodied Chrysler cars have known PCM issues, Chrysler partnered with an outside company to supply PCM's for those cars. The dealer even said that that is where they get there PCM's for those cars from. The service manager said basically that Chrysler was, as he put it, "washing their hands of the early LH bodied fiasco". I did find out though, that the company is very easy to deal with, in terms of returns and replacements. They are even sending a replacement PCM, and said not to send the other one back, until we get the replacement. On a side note, i use a site called factory chrysler parts, that will show a breakdown of every part and part number of every part used in any Chrysler/Jeep vehicle from 1984 to current vehicles. That is how i found the original part number for the PCM, but, when i went to the dealer, they said it wasn't available, and that is when the service manager said try the place we got it from.

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We're all getting resourceful as the internet grows and gets more sophisticated.  I'm interchanging parts at Mopar sources in minutes, a task that took forever years ago when we worked with microfiche at dealerships!  Glad you're on the home stretch with the LH.  Let us know how the Ford Explorer transmission fill turns out!

Moses

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An update on this one. After 5 returns, we finally got an ECM that actually worked, only to have the car quit a week later for a bad cam sensor, then quit a few days later for a bad starter, then, a week after that, both rear struts collapsed at the same time. Now though, hopefully it is all done and over with.

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