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Chris
Chris, Shop Foreman
Category: Jeep
Satisfied Customers: 13866
Experience:  Jeep Certified Master Tech
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Cherokee: I have a 98 XJ. MIL on; DTC p0300 0306 0301. Changed

Customer Question

Hi I have a 98 XJ. MIL on; DTC p0300 0306 0301. Changed coil, plugs twice, wires twice, cap and rotor twice, new battery, pressure test on all cylinders between 125 and 149 psi (#2 was 125). swapped injector 1 & 2 misfire did not follow. same for 6 & 4 swap. No detectable vacuum leak. Freeze frame -STFT 3% LTFT 0%. 748 rpm 42 kmh. ECT 95 C. performed fuel pressure test - flutters @ 45-50 at idle slight flutter @ redline @ 45. noticed bubbles in fuel when I drained off pressure. am I looking at a fuel problem? could I have a bad valve and sill get compression numbers observed?
Submitted: 2 years ago.
Category: Jeep
Expert:  Chris replied 2 years ago.
Hello, my name is***** you for allowing me to assist you! I have seen issues like this being caused by excessive carbon build up on the valves. It may also be a valve seat issue. I do not think it is a fuel problem because your STFT and LTFT look fine. Do a decarbon procedure using a couple of cans of Sea Foam or other quality decarbon product. If the problem continues, then pull the head and check those valves seats. 9 times out of 10, the decarbon procedure usually works.
I hope this information helps, and please let me know if you need further assistance with this.
Chris
Expert:  Chris replied 2 years ago.
Hello, just checking back to see if you received my last reply, and if so do you still need help with your problem?
Chris
Expert:  Chris replied 2 years ago.
Hello, just checking back to see if you received my last reply, and if so do you still need help with your problem?
Chris