2004 Jeep Liberty not getting ignition coil signal from PCM

[Sk8Crash69]

Hello Everyone, I just recently purchased a 2004 Jeep Liberty with 3,7L engine. The engine has a rough idle and 2 CEL codes P0304 and P2311. I have given the Liberty a full tune up with new plugs and tested and swapped the coil on cylinder number 4. the coil was bad and replaced with a new and tested coil. After trouble shooting the code I can see that the PCM is not sending a signal to the coil to fire. I have test the wiring from the PCM to it is good, no breaks. From what I can see form research I have done, my option seem to be bad PCM, bad crankshaft position sensor, or bad camshaft position sensor. I have no other codes, the misfire is noticeable at idle and on acceleration. Is there any way for me to test those components or narrow down the problem? I do not just ant to recklessly start replacing parts. Thank you.

 

[tjkj2002]

Your looking at a failed coil driver in the PCM if the wiring is truly good.

 

[Sk8Crash69]

Ok, a bad coil driver would mean a PCM replacement? Could the original bad coil on cylinder #4 have shorted out the coil driver in the PCM? Should I not be looking at the crankshaft position sensor or camshaft position sensor?

 

[Logan Savage]

I had a bad injector fry the injector driver in the pcm so I'd imagine a coil could too .

 

[Sk8Crash69]

Yeah I am definitely leaning towards the PCM. I have been reading that A1 Cardone's are pretty much the only half way reliable option, besides the dealer who wants $2000 for a new one. Who do you guys recommend for a PCM and programming. I was checking Ebay and see that there are some sellers that also program PCM's. Has anyone had any experience with any of them?

 

[Logan Savage]

I bought a plug & play pcm off ebay . If you go this route make sure it's guaranteed . It's been a while but I think I paid a tad less than $150.00 .

 

[Billwill]

When you check the wiring to the failing coil you need to completely remove both wires going to it ie. at the coil itself and at the PCM connector (unplug the wires at both ends).

Then with an Ohm meter measure each wire from end to end for less than 1 Ohm resistance..make sure you are not touching the meter probes with your bare hands.

Now check that there is absolutely no connection from one wire to the other.

Finally with the two wires still disconnected at both ends make sure there is no reading at all from either wire to the engine block...it may be chaffing through somewhere.

Re-plug the PCM connector a few times to clean its contacts....if all the above does not help then a new PCM is probably required.

Bear in mind that if you have a shorting coil lead or bad coil and you do not first repair them then putting a new PCM in place will straight away blow the new PCM!

 

[Sk8Crash69]

Hello everyone, just wanted to provide an update for anyone that might have the same problem as me in the future. I purchased a PCM off of Ebay, where the seller offers free programming and installed it today. Well it did fix my misfire issue immediately. Thanks everyone for your help.

 

[david.lukac]

I had the same issue - Cyl4 missfire, codes P0304 and P2311. I changed spark plugs and ignition coils, plug was wet from the gas to injector seemed to be OK, there was continuity on wiring between the ECM and the coil. After some research and reading terrible reviews about bunch of vendors selling rebuilt ECMs I ordered from FlashMasters for a great prices. So far after couple of hundreds of KM everything seems to be OK, fingers crossed the unit will serve good couple of years.