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Chrysler Repair/2002 Jeep Tj 4.0 codes P0300,P0301,P0306


I have replaced the following,4 O2 sensors, camshaft position sensor, crankshaft position sensor, map sensor, throttle position sensor, air temp sensor, all were Mopar. I have put on a new exhaust system including 3 converters. New fuel header, new spark plugs. Still have a dead miss. Don't know what to try next. Thanks Mike

Hi Mike,
While I don't have the '02 manual so can't be sure of the spark coil situation, but rather I have the '06 manual.
While you have replace many parts, it appears that you have not looked into the spark coils.
I do notice that on that '06 year the 4.0L uses a 3 section spark coil "rail" and that the plugs for cylinder 1 and 6 are fired by the same section of the coil rail. Because the miss is evidently on cylinder 1 and 6 (based on fault codes 301 and 306) that suggests to me that either that specific section of the coil rail is faulty or the driver wire for primary winding of that section is damaged. It is shown to be a wire that is dark blue/dark green and connects from pin 10 of the number 2 plug of the pcm to pin 1 of the 4-pin plug of the coil rail. So check out that wire (or a similarly assigned wire if your '02 is a different coil set up).
If the driver wire is OK, then my suggestion would be to check the primary winding and the secondary winding resistances for the section of the coil that powers the plugs on cylinders 1 and 6. The primary winding should be 0.7-0.9 ohms, and the secondary about 12,000 ohms.
The last possibility is that the coil capacitor, mounted on the right side rear of the cylinder head is faulty. However that capacitor is connected to the common 12v supply to all three section of the coil rail so it is unlikely to cause a problem with only one of the 3 sections of the rail. But I mention it to be complete.
Please read the PS (below) and respond to it.

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Roland Finston


Get a Free Fast answer to your repair question about a Chrysler/Dodge/Plymouth car, minivan, SUV, or truck. Problems with electronically controlled engines and transmissions as well as body wiring problems are my specialty. This free troubleshoot advice forum helps you diagnose faults, minimize repair costs or do-it-yourself.

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