ghttbnz

1999 WJ Jeep Grand Cherokee Limited 4x4 4.7L V8 engine WON'T STAY RUNNING UNLESS YOU PRESS THE THROTTLE PEDAL, at idle it wants to die and it does, soon as you let go of the pedal it dies, when you come to a slow down/stop it dies, the only way to keep it going is to rev it up.

Now i got it this way and whoever worked on it first started to throw parts at it so all the sensors are new:

crankshaft position sensor (OEM)
camshaft position sensor (OEM, not sure about, i cant tell if it looks new or not, but they told me they replaced both)
TPS
IAC
MAP
Evap Solenoid
Upstream oxygen sensor (not heated in this jeep)
fuel filter/pressure regulator

I put in:
new copper core champion spark plugs with correct .040 gap, double checked gap and part numbers, old plugs were old and dry fouled.
new starter and battery


Its definately running rich, smell gas, black DRY soot on new plugs already. Had bad battery, I replaced the battery and starter with new ones becuase they were crap. It cranks well and starts right up with help of throttle pedal. have to press throttle to keep it from dieing. Hooked up Snap-On Solus scanner and get the following codes:


P0443 (evap solenoid) checked it it opens and closes fine, was originally installed upside down so i turned it right side up (connector on top) and it still throws code, leads me to believe it is related to my main issue, so i am leaving that alone for now.


P0351-P0358 throws ignition coil codes all the time, multiple codes and different ones every time, NO MISFIRE CODES, but car does feel like its running ok with throttle pressed then shakes a little when the actual check engien light gets thrown, which makes me think its misfiring, and shutting down a coil or few at this time. tested coils with ohm meter all within spec. PCM maybe, problem with either the PCM coil drivers or monitoring system?


fuel pressure tested at fuel rail with snap-on guage at schreider valve, PSI is great at 55-60 PSI. It does not lose pressure when car dies. ASD relay DOES NOT shut down fuel. So i am ruling out fuel delivery to the injectors, but not sure about the fuel injectors?

I do not have a vacuum leak, visual inspection, and scanner live data ALL checks out.


I am stumped. Any help will be greatly appreciated.

Dans99WJ

Sounds like a computer problem. A lot of time with issues like that, where replacing the sensors and the code still get thrown up, its your main computer gone bad.

aleet25

I had the same problem last week. Took it to my mechanic and sure enough it was the PCM that went bad. He told me an easy way to test it is to take the PCM out of the car, but leave it plugged it, and wrap it up with plastic and drop it in a bag of ice. Once it gets cold, start your car up and let it run. If it starts up fine and runs, then there is your problem.

ghttbnz

thanks for the help, i figured it out.

I replaced the computer with another used one, programmed it with the drbIII scantool for sentrylock so that it starts the jeep, still no go, same condition. So i started to go over everything again, checked all my grounds in the engine bay, unscrewed them and sanded them down, didn't think this would help but it can't hurt. Then I took out the camshaft position sensor as my problem seemed to be that the computer is getting a bad or no reading from a crytical sensor, as a listed in my original post, i was told this was replaced, and this one is really hard to tell if its new or not, so i decided to pull it out anyway, first off i didnt like the sludgy oil on it, second the connector plug was drenched in something, coolant or oil, something, so i used electrical cleaner on plug and let it fry for a few hours and i replaced the CAMSHAFT sensor, and changed oil for some good fresh stuff, WALAH! Jeep starts right up, idles perfectly at 650rpm, runs fine, drives fine, engine purrs like a kitten, no codes in computer, never ran better, on a side note i did plug in scanner again and in the history data, now it showed a code for CAM/CRANK sensor fault, now that everything was running right i see a history code, no current codes, so all is good, too bad the computer didn't throw that code to start with!

04WJ

hey i think i have the same problem lol
i put gas in my jeep nad it would not start got it towed home. changed cps sensor and fuel filter idk anymore. what was your problem ? what is it called ? i need your help

scottwoodd8

i have also encountered this problem last summer and i have no choice but to bring my car to the mechanic and have some Jeep service that's way off my budget. my only advice for you guys is to maintain your jeeps properly so that you wouldnt need to do what i did anymore.

Bustedback

It's the idle air control motor causing the engine not to idle unless you have your foot on the gas.

Dans99WJ

Congrats on fixing the problem!

Ren2000WJ

I know this is an old thread, but I'm posting this to let WJ owners know what I found after changing every sensor:
Crank sensor
Cam sensor
MAP
IAC
ASD
Out of frustration (And stubborn Irish ancestry) I started tearing into the wiring harness when my WJ went from intermittent to NO start / No codes... After hours of painstaking work, I found that my CRANK position sense wire had melted and caused a "direct short to ground". I traced the wire to the PCM harness and soldered a new wire from the pcm connector to just above the plug. Made sure all of my fuses were good, and charged my battery to ensure adequate voltage (it was drained from testing, cranking etc.) And away it went...no more issues.

My advice is to look there first. Use a voltmeter and test light to check every wire in the CKP /CPS circuit and don't lose hope... Tell me if it helps

dave1123

Yeah, a crank sensor won't throw a code for a scanner to read, but it will for a "key" code. IDK why, but it happened on my 00 WJ.

mobile-command-unit

funny coincidence; I once replaced the camshaft position sensor assembly with a cheap part. When I started it up it would barely run. It threw all kinds of codes. It was installed correctly as well. I took it out and put the old one back in and it ran great. There is definitely a trend with jeeps requiring mopar sensors!