Help with rough idle and acceleration - TIA

Sep 09, 2005 39 Replies
2004 Jeep Grand Cherokee Limited Inline 6 Cylinder Engine Automatic Transmission Stock - No modifications

Symptoms: After car warms up (3-5 Minutes) the engine idle drops to about 600RPM and the car starts shaking rapidly. When you accelerate the car shakes repeatedly between 600RPM and 1500RPM. At 50 miles an hour, pressing the accelerator slightly to maintain a steady velocity (which is about 1500RPM) the car will experience the shake while driving. Moderate acceleration the problem goes away. Lifting off of the gas and the problem goes away until the above rpm range is reached and then problem comes back



Followup: Computer diagnostics indicates a miss fire on cylinder # 5



Question: Could this be a clogged injector or are there other suggestions?



TIA Ken


Don't each of the coil packs handle 2 cylinders? Wouldn't both misfire?

That's the 4.0L, not the V-8. 4.0L I-6 uses three coil packs, one per two plugs.

Only an open circuit would misfire both plugs on a lost-spark ignition... a fouled plug merely helps the other plug fire. __ Steve .

You said a failed coil would not kill 2 cylinders. It will, and that is what I was responding to.

Would have looked similar to this Japanese:

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The 3 coils dual-fire the spark plugs on cylinders

1?6, 2?5 and/or 3?4. When one cylinder is being fired

(on compression stroke), the spark to the opposite

cylinder is being wasted (on exhaust stroke).

(From page D-3 from CD Manual for 2000 WJ Ignition System Description and Operation)

My point is that if you have a bad coil you will have 2 cylinders mis-firing.

Oh, so the waste spark system on the 4.0L different than the waste spark system on any other engine? Please explain.

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