Interesting ignition problem - Solved

[poconoracing]

Posting this in case anyone else comes across this problem

 

My 2010 GT - 134k miles would suddenly stall, like someone hit a kill switch. Completely randomly, with no consistency on the time run, temp, weather, etc.

 

No CEL, no other symptoms, car would crank but not fire. Come back it it later and it would sometimes fire right up.

 

Diagnostics verified crank signal, fuel injector pulse but NO spark at any of the 4 coils.

 

At the coil plug had power, ground but no control signal at any of the coils. Thinking the drivers in the ECM went bad, I went after the ECM behind the dash. I verified powers and the main grounds. I was just about to condemn the ECM when I noticed on the ignition wiring diagram the ECM has grounds that run through the Engine harness back to the grounds under the hood on the drivers side of the intake.

 

Turns out they run through PINS 34,35,36,37 and 40 of the large engine connector. They are the larger pins in a left to right row in the center of the plug. In my case #35 had been bent in slightly and was breaking contact intermittently. using a dental pick i bent it back into place and no issue since. No one has touched that plug in better than 2 years, really odd failure.

 

But nothing better than a cost free repair

 

Edited to add the wiring diagram from the FSM for the ignition.

ignition.pdf

Edited June 4, 2022 by poconoracing

[Infosecdad]

^ Thanking this post

[FLlegacy]

Thank you!

[Scubaboo]

Good work tracing that! I can imagine that being a b!+@# to find.