thezfunk

1998 Cherokee 4x2 4.0L

I have had an issue that has gotten worse the more parts I have replaced. The Jeep starts and runs just fine. I get between 19-21MPG. However, the first time I accelerate on a cold start it will stumble or possibly misfire until I get to about 2000RPM. It will sometimes stumble bad and I hear like an air pump sound, if that makes any sense. After the initial acceleration, the problem mostly goes away. Lower RPM's do tend to have a feeling like the Jeep is in sand and a sluggish acceleration feel. Then, at about 2000RPM it takes off.

In the last 30k-40k I have replaced the following as part of general maintenance and also trying to diagnosis this issue.

new plugs, wires, distributor cap and rotor
new air filter
cleaned throttle body
new TPS, MAP Sensor, IAC (Idle air control? Basically any sensor on the throttle body)
New 4-hole injectors (highly recommend)
new fuel pump assembly
new cat, muffler and tailpipe
new upstream (once) and downstream O2 (twice)
new valve cover gasket
new PCV valve, gasket and breather elbow and gasket
new battery
reset PCM

I think there are only a handful of sensors left but I am sick of picking something, changing it and not getting any results.

Twice now, I have gotten a P0420 code after I replaced both 02 sensors and the cat. One, I think, was the fact my downstream 02 sensor wire was laying on the drive shaft and it wore it through down to the bare wires. The second I couldn't explain and I just cleared it and it hasn't been back.

Could this be a spark thing? Ignition coil? Distributor pickup coil? I am literally running out of parts to change. Crank sensor? camshaft sensor?

I am sure the diagnosis will somehow involve an analog volt meter but bring it on :-D

Muaddib420

I don't know man looks like you've changed just about any part that can be changed. My initial guess would be MAP sensor since it only stumbles when cold. But you've changed that.

Might be time to bring her in to a reputable Jeep shop for a fresh set of eyes.

partsguyct

I'd look into swapping the distributor, had a similar issue on my '93 and that was the final fix. Just my 2 cents

thezfunk

One of the other Jeep forums suggested I try checking the timing with a 'toothpick' method. I was told to search. Unfortunately, all references to it go to a dead article....

DisposableHero

You seem to have changed everything except for the fuel filter....

although that would give you bogging at all temps.. not just cold in the morning.

PS my truck does this too. It appears to have been two issues since I fixed one of them by replacing the plug wires - one of them would short out on the block when it was moist in the morning dew.. I caught that one by complete accident, just happened to have my hood open one morning when it started doing it and I saw the arc.

thezfunk

I think I found the article they were talking about.

https://docs.google.com/viewer?a=v&q...-PQY2vx-Yj_ypw

and

http://www.jeepforum.com/forum/f11/h...ensor-1145301/

I think I am also going to check my coil.