96 JGC Cold Start Engine Misfire Problem PLEASE HELP!!

[Judge0275]

Hello,

I am new to the postings and I am having a serious problem. ANY HELP PLEASE.

I have a 96 JGC 4.0L InL6 Limited 270k miles runs great. However when the vehicle has sat overnight and I start it. If I raise the RPM's to 2200 - 2500 the engine starts misfiring like it wants to die. If I let the vehicle idle for 10 - 15 mins (Normal Operating Temp) it goes away. I have changed the PCM (2), IAC valve, TPS, MAP, Manifold temperature sensor, O2 sensors (Both), Crankshaft Position Sensor, Cam sensor, and Water temperature sensor. This also occurs if I try to drive it before it has reached normal operating temp. I have done a tune-up (Plugs, Wires, Cap and rotor) I have even changed the coil. The fuel pump appears to be working correctly. I have preasure at the fuel rail leading to the injectors. I have test the injectors and they a are reading 12.4 to 12.6 ohms at each injector. I have no Idea whjere to go next. Any help would be greatly appreciated. Oh and I have also tried taking it to a shop. Their answer "we can't seem to find the problem". Why does this not supprise me. There is no oil in the water or water in the oil so I am not suspecting craked heads or block. also cylinder preassure is good on all cylinders. PLEASE HELP IF YOU CAN. Thank you!!

John

[leowolf]

Wow great desciption! no kidding.. does it start and idle ok or does it die intermittantly, im thinking vacuum leak. but its sounds like you are inclined so im thinking you've gone there...hum does the vehicle smoke? this is a shot in the dark so to speak but when the valve guides go bad they become a vacuum leak. Using oil like a quart every other fill up?
and the engine smokes pretty bad at idle? wow thats a lot of miles.

[Judge0275]

Okay everyone.. Thank you very much for all your help. I have solved the problem. The problem was not a sensor problem but it actually was within the engine. I got tired of chasing my tail in circles. I pulled the engine out and had it overhauled. Walah!!!! It turns out that I had (3) bad lifters. and every piston had signs of blow by. Well what do you expect when you have a motor with 272K miles on it. Well I got the motor all installed and fired her right up. she ran but had no power. I took her to the shop and had things tested just to verify. all was right. Except. The shop sugested a timing issue. Hmmmm I thought maybe I better look at this. I pulled the timing chain cover and through trial and error I discovered that I had installed the distributor 180 degres off. Oopps!!! Well I have fixed the problem and she has her power back. Amazing the PCM adjusted for all that and she still ran. Everyone I have talked to said I am surprised thet it even started. Well she did. I love my Jeep. So thanks everyone again especially Dale. that guy is great. Take care everyone and I hope this may help anyone else out that is frustrated over the same issues.