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Discussion Starter #1
I have a 2004 Lightning with 22k miles, I've had it for about 8 months and the ignition system is all stock and original other than plugs. I've been having an issue for the past couple months of the engine missing out intermittently when cruising at a steady speed with minimal throttle. First I changed out the weird old copper plugs that had a really short ground strap for some OEM motorcraft plugs since I could get a hold of them quickly. The issue was still present, so just this week I put in some NGK TR6's and gapped them to .034 for the 14-15psi of boost its running. The issue is still present. I'm beginning to assume that it's most likely the ignition coils since they are original and have sat around unused for most of their lives with previous owners and they are just going bad from age. Also if I'm at cruising throttle and it's misfiring, I can let out to very light throttle and I can feel the engine smooth out. Same with full throttle, I'm pretty sure it fires on all 8 but who knows, it could just be powering through the misfires and I'm not feeling it. Does this sound like an ignition coil issue?

Thanks for the help
 

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Dude
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I would also check the Cats for excessive back pressure. If they are clogged up you can check them yourself with an infrared thermometer or take it to an exhaust guy have do a back pressure test. My last three vehicles all had clogged cats. The fact that it is smooth when your light on the throttle tells me this could be the case.
Good luck these are fun trucks when you get them sorted.

Sent from my SM-G950U using Tapatalk
 

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Discussion Starter #7 (Edited)
Well I just replaced all of the coils for new Motorcraft coils, I had hopes that the issue would be fixed but the issue is still there even after new plugs and coils... The truck runs great other than the certain throttle position that starts to misfire when cruising at a steady speed or very lightly accelerating (so maybe like 5-15% throttle roughly). I just checked the plugs that came in the truck when I bought it and they are Autolite Racing AR94 plugs gapped around .032, I gapped the new NGK TR6's at .034 so maybe decreasing the gap might solve the issue? Could this be a fuel issue such as an injector or fuel filter possibly? I don't really think this is a tuning issue since this problem wasn't present up until a couple months ago. Maybe the cold winter air is affecting it and it was tuned in hot weather? I'm not sure but I will try decreasing the gap to match what the old plugs which I assume were in the truck when it was tuned. Maybe putting in new AR94 plugs at the same gap would fix the issue since the truck was most likely tuned with those plugs and I never had issues with them except for a misfire at full throttle, which is why I replaced them.

Also I should mention that the truck has catless exhaust, throttle body, intercooler, ported plenum, ~14-15psi boost, CAI, 3000rpm stall and a few other things, so clogged cats isn't an issue.
 

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Discussion Starter #10
Again, if the EGR system is still in place, you most likley have a DPFE sensor that is bad.

JJ
Well it looks like this was the problem, I popped off the little EGR valve vacuum elbow and put a screw in it and took it for a drive and the problem disappeared. So in this case this means the DPFE sensor is dumping too much exhaust in so I would need to replace that part? Or would it be worth it to do an EGR delete?
 
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