What I have: 2004 Jeep GC 4.0L automatic transmission 4WD.


The problem: The engine Idles fine however while under load (accelerating) the check engine light flashes and eventually the engine sputters out as if it were only firing on 2 cylinders and was horribly out of timing. Almost a complete loss of power and usually happens over 55 MPH and above 3000 RPM. When I turn the engine off while moving and then back on, the problem goes away for about a minute and then comes back. Its all intermitent though, sometimes it runs like a dream.

List of Codes: P0340, P1490, P1489, P0300, P030X-1,2,3,4,5,6, and P1391

What I've done: replaced...

-Spark plugs (copper core Champions)
-Ignition coil
-All 4 O2 sensors (Denso)
-Fuel Pump (Delphi - It could be bad, I can hear it come on and there is a mostly constant high pitched humming coming from it. I only replaced it because I was having some starting issues and a mechanic said I had low fuel pressure. The starting problem was solved.)
-Fuel Filter (Fram)
-Camshaft Position Sensor and Synchronizer (Duralast - It was professionally installed but I am not confident in their work because that P0340 code came back a while after they replaced it.)
-Check for vacuum leaks and I found none. Missed one perhaps?

Any help you guys could give me would be awesome. I'm out of ideas unless the mechanic didn't do the CPS right. I've thought about the Crankshaft PS but I thought that really only affected the idling.

 

have you pull off your distributor cap and checked the connections for corrosion? Lack of signal could do that. Based off what you replaced so far, the next thing I would look at would be your PCM.
Your jeep has codes for when your PCM goes out so you know to replace it but if the PCM is totally screwed to the point it wont fire a code or possibly the correct code how will you know?
You have to change it to find out.


Back when I was dealing with my stalling jeep problem last year one mechanic kept telling me if my PCM was bad then I would get a code.


My new mechanic at Team 1 Automotive here in Alpharetta Ga told me they were going to replace it and BANG, the thing was running fine after that with a few exceptions... I had to get some wires repined as well but bottom line was, the PCM was bad and wasn't firing codes.


So your PCM may be malfunctioning to the point were it thinks something is wrong so it makes adjustments to system to compensate for this or that cause you to actually misfire because the signal is being disrupted.


A PCM is about $200 new.... Its kind of expensive Advil, but your headache will possibly go away

 

This year of Jeep does not have a distributor. Its all done electronically to my understanding. Do you know of a way to test the PCM before I dish out $200 to fix the problems?