Understanding Ford Expedition 2014 Ignition & Fire Event

  • AguilarPro
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03 Mar 2021 22:57 #47209 by AguilarPro
I'm trying to understand this waveform signature, I back probed the two wire ignition coil #1 & #2, scanner was giving me a misfire on cylinder 1 by using engine speed, it was calculating the misfire, the misfire was stored as random & also had DCT for cylinder 2 misfire. I did not trust which one was actually misfiring because of a calculation by "engine speed" of each cylinder it determines a miss.

First picture is #1 coil and second is #2, the main difference that I noted was the burn time was too long for #1, or perhaps too short for #2 due to partially cloggled fuel injector? I swapped coils and plugs and the issue seemed to remain at #1 (as calculated by the PCM). The miss was reduced by just doing this but I was not convinced it was fixed since it was still having misfires not obvious. Unplugging the coil was not too noticeable for #1 but was for the others. Fuel trims were also opposite from each other, for example, if I reved the engine, one bank would go lean and the other one would go rich during acceleration.

Someone that is more familiar with this waveform signature can probably help, I measured the burn time for each to see if I can get some sort of feedback on what this could mean. Let me know what you guys know or think about this. Car has been delivered by changing coil and plug as it was rushed but I was not convinced the coil or spark was defective, I checked the coil and it had good spark.
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  • Chad
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04 Mar 2021 09:57 #47222 by Chad
I would raise the RPM's to switch the coil to a SINGLE firing event.

"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer."

I have learned more by being wrong, than I have by being right. :)
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  • Tyler
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04 Mar 2021 20:10 #47231 by Tyler
Based on the waveforms alone, it looks to me like the #1 spark is arcing across an air gap to ground. That'd be why the burn time is considerably longer, and that there's no turbulence in the burn line. Carbon track, hole in the coil boot, like that. Possible coolant in the plug tube as well. Tough to tell based on a primary waveform.
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12 Apr 2021 21:57 #48184 by AguilarPro
I got some time to look at this Expedition again and I did a relative compression test using an amp clamp on the negative battery terminal. I'm afraid I may be looking at mechanical, I could not put a trigger because I was using clear flood mode and I did not bother to remove the fuel pump relay. I see 3 low and the 1 lower which I believe is the cylinder #2 that is being flagged by the PCM. Long trims are opposite and they stay that way when revving up, I also noticed that the miss/stumbling of the engine is not all the time, kind of comes and goes, this is also visible on the trim data but there is not a consistent failure, this is the reason I decided to run a relative compression check, I will do in-cylinder to see if I can spot something obvious at the valves, etc.
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