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post #1 of 5 Old July 24th, 2010, 07:06 AM Thread Starter
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Exclamation Diagnosing a dead cylinder

I was driving my stang last night and then all of a sudden I felt a cylinder go out, change in sound on the engine and could feel that vibration. So I get back home and start pulling the COP connectors and figured out it's the 2nd cylinder back on the driver's side, I believe that's cylinder 6? When I pulled that COP plug there's no change in the engine, so I tried swapping the COP with another one and the same cylinder stayed dead. I also compared resistance of the spark plug from top to tip and that's the same as another so I don't think it's a plug either.

I looked in the online service manual at the wiring but I don't know how to figure out which PCM plug the COP wire I need to trace goes into. On the schematic it's got a number 15 at the PCM side and along the wire there's number 1025. Ford Service Manuals - Wiring Diagrams

Does anyone know which connector the wire is in? Top, middle or bottom? I guess I should also check the wires for the fuel injector since no fuel would most likely cause the same issue.

Thanks for any help you guys can provide. I need to get this figured out this weekend so I can install the supercharger next weekend.


300 stroker, 11:1, 7L2E iron block, 3.73's, MT ET Street Pro's. UPR solid LCA's, JPC race UCA. Kooks 1 3/4" LT's with 3" O/R H. 9.988 @ 136.55mph, E-Force with 3" pulley running E85. Tuned by Manuel from TUDYNO.
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post #2 of 5 Old July 24th, 2010, 08:49 AM
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You need to do a compression test first. If you find a dead cylinder remove that side valve cover and inspect for a valvetrain issue. I'd do this before starting the engine again. If you have no obvious valvetrain issue, but a dead cylinder, sadly, the engine will probably have to be removed or at least pull that side's head for inspection.

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post #3 of 5 Old July 24th, 2010, 02:55 PM Thread Starter
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The odd thing is that it happened just like a switch was flicked. I finally go a code and it was a coil code. The weird thing is that the code says coil F which would be cylinder 5 but the one that's not functioning is cylinder 6. I confirmed that the correct wires are going to the correct coils so it's quite odd.

I'll be stopping by a guys shop tomorrow and we'll pull the cover as well as put a scope down the spark plug hole.

300 stroker, 11:1, 7L2E iron block, 3.73's, MT ET Street Pro's. UPR solid LCA's, JPC race UCA. Kooks 1 3/4" LT's with 3" O/R H. 9.988 @ 136.55mph, E-Force with 3" pulley running E85. Tuned by Manuel from TUDYNO.
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post #4 of 5 Old July 25th, 2010, 06:22 AM Thread Starter
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Well, it was one of 2 things. I picked up a new spark plug and at the same time took the boot off the COP and cleaned the old grease and dirt from it as well as cleaned the spring real well. The combination of those 2 things fixed the issue.

I think there was too much dielectric grease in there causing an issue but I'll never know since I did both at once. Next weekend when I start the install of my E-Force I'll clean out all the COP's when changing to HT0 plugs that way it's all nice and fresh.

Thanks for the reply.

300 stroker, 11:1, 7L2E iron block, 3.73's, MT ET Street Pro's. UPR solid LCA's, JPC race UCA. Kooks 1 3/4" LT's with 3" O/R H. 9.988 @ 136.55mph, E-Force with 3" pulley running E85. Tuned by Manuel from TUDYNO.
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post #5 of 5 Old July 25th, 2010, 08:31 AM
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That was easy. I guess you're relieved.

JDM 302 Stroker, Whipple 10 rib 12 psi, L&M, JBA, J&M, LFP, Corsa, Stage II cams, Manley, MGW, McLeod RST, Eaton Posi, 3.73's, Metco, Steeda, Autometer, CDC, Street Scene, SOS, Tuned at JPC Racing by Kevin MacDonald....Other Mustang 2015 GT Premium
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