Help with Cylinder 4 misfire 2013 mustang gt auto base

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    Icon5 Help with Cylinder 4 misfire 2013 mustang gt auto base

    I bought a salvaged 2013 mustang gt wrecked in front, minor damage with (110,000k) It had a BBK long tube headers with 3 inch x pipe and welded back pipes and roush exhaust. The code 304 had been there. I am a mechanic who has done a lot of rebuilds on other mustangs. I have an IDS non-commercial VMCII with laptop. Code p 0304, cannot eliminate it no matter what I have done. Ford said I need new long block $. I have taken the motor out and sent heads to machine shop, result: heads reworked no ridge on cylinder. all bearings good. re-ring the block, new head gaskets, ARP bolts, new coils , new injectors, new spark plugs, changed wiring harness, changed O2 sensors, relearn neutral profile correction with IDS. Checked PCM with computer (all modules passed).Compression is 160, fuel pressure 55, vacuum 52, leak down at 12psi on first gauge, 2% on second. Need help, code doesn't go away. Power balance -29 shifting in cylinder 4. Exhaust was changed back to original using Eastman cats and stock mufflers. changed the lifters and followers because it was apart. Any help would be good. thank you ED. P.S. New user to the IDS system.

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  3. #2



    Congrats on the new ride and sorry to hear about the persistent code.

    I'm only a shadetree mechanic so take that for what it is worth. :D

    Have you checked the crank timing ring? It is sintered metal and I'm thinking that a hard rap to the engine may have chipped or cracked the ring or a tooth.

    Has the crankshaft been checked for excess play (front-to-rear)? I don't know if this would cause an isolated issue (one cylinder misfiring) or all of the cylinders but if it is out of spec then maybe it is something to correct.

    Have you checked the wiring harness? Perhaps it got pinched in the accident and there is a short (intermittent short)?

    How's the intake look? Any cracks around cylinder 4? Got a friend who will let you test a different intake (stock, just a different one from what is on the car now)?

    What about the injector? I'm stuck on the jarring blow a root cause for P0304, as you may have noticed.

    That's about all I can think of. I hope you can track down the problem and get your engine purring like a kitten soon.


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