[302SS]

Originally Posted by mstgeer

Have you resolved this issue? My stock, except Holley CAI and oil catch can, '17 2ss with 15k miles is doing the same thing, random misfires (not all the time, but seems to be progressively more frequent), not enough to trip codes or trigger the check engine light. Runs rich on cold startup (black smoke out exhaust). Checked fuel trims and getting negative values.

Does checking the resistance of coils generally result in accurately identifying a bad coil?

I haven't, been going on all year. I swapped coils and never got the issue to move.

[mstgeer]

Originally Posted by 302SS

I haven't, been going on all year. I swapped coils and never got the issue to move.

From internet research, injector going bad can cause same symptoms. I hope to have time tomorrow after work to trouble shoot my issue further. When I get a resolution I'll be sure to make a post.

[Patriot Motorsports USA]

Originally Posted by 302SS

I haven't, been going on all year. I swapped coils and never got the issue to move.

Do you track your car or have you had the chance to put it on a Dyno?

I will be back in the States this weekend, feel free to reach out and give me a call. I would love to help you narrow down what could be causing the misfire as I had the same issues with my ZLE when it was new to me. I changed the plugs, wires and all sorts of hoops to jump through and it was simply the system that was failing me. Once I removed the oil cooler and changed my setup, results were easy with zero misfires in a year. I have been running the same plugs since Feb this year with zero issues now and thousands of track miles.

[mstgeer]

Well... it's off to the dealer for diagnostics. Misfire in cylinder 7, did not change locations with the swap of the coil and wire to cylinder 1. Thinking it has a lifter on it way out, only 15k miles.
Will report back with findings.

[arpad_m]

Wouldn't be a surprise, since cylinder 7 has an AFM lifter that is known to collapse over time. If that's the case, now will be the best time for a DoD delete + tune combo to prevent the other three (1, 4 and 6) from doing the same.

[mstgeer]

Originally Posted by arpad_m

Wouldn't be a surprise, since cylinder 7 has an AFM lifter that is known to collapse over time. If that's the case, now will be the best time for a DoD delete + tune combo to prevent the other three (1, 4 and 6) from doing the same.

Fortunately, the car is still covered by GM Platinum Service Contract with $0 deductible.

[302SS]

Originally Posted by ZLElvira

Do you track your car or have you had the chance to put it on a Dyno?

I will be back in the States this weekend, feel free to reach out and give me a call. I would love to help you narrow down what could be causing the misfire as I had the same issues with my ZLE when it was new to me. I changed the plugs, wires and all sorts of hoops to jump through and it was simply the system that was failing me. Once I removed the oil cooler and changed my setup, results were easy with zero misfires in a year. I have been running the same plugs since Feb this year with zero issues now and thousands of track miles.

I have not, I would appreciate any help. I haven't tracked my car ever, it's been on a dyno when it got tuned a year+ ago. Going to finally get it into my brother's shop to test injectors/possibly clean and check grounds tonight.

Originally Posted by arpad_m

Wouldn't be a surprise, since cylinder 7 has an AFM lifter that is known to collapse over time. If that's the case, now will be the best time for a DoD delete + tune combo to prevent the other three (1, 4 and 6) from doing the same.

My car is cammed, all that junk was taken out 9500 miles ago. :(

Appreciate all the help/comments guys - will be trying everything.

[KingLT1]

Originally Posted by 302SS

My car is cammed, all that junk was taken out 9500 miles ago. :(

Appreciate all the help/comments guys - will be trying everything.

Originally Posted by mstgeer

Fortunately, the car is still covered by GM Platinum Service Contract with $0 deductible.

Dealership isn't going to cover a car that has an aftermarket cam/valvetrain. You would be better off taking it to a reputable performance shop.

[mstgeer]

Originally Posted by mstgeer

Fortunately, the car is still covered by GM Platinum Service Contract with $0 deductible.

Initial diagnosis from dealer is that #7 plug wire was not fully seated, causing intermittent continuity with the spark plug, causing the misifire and the plug to foul.
Strange thing is, I bought the car as a dealer demo car with around 5k miles on it and it has never had any work done other than CAI, catch can and brake pads (all installed personally by me). It has always had a slight intermittent miss at idle which I chalked up to being the typical 6.2 idle lope.

Maybe the trip down the BOD & TOD at the end of June shook it loose,

They are trying to get $400 out of me for diagnostics and 1 plug and wire when the car is covered by the GM platinum protection plan, which is exclusionary and does NOT exclude spark plugs and wires. They played dumb until I offered to provide the contract number, then, mysteriously, should not need it, it should be in the system. They will likely not approve, but we will call them for approval and let you know.

Guess there is validity to their nickname "stealer".

[mstgeer]

Originally Posted by mstgeer

Initial diagnosis from dealer is that #7 plug wire was not fully seated, causing intermittent continuity with the spark plug, causing the misifire and the plug to foul.
Strange thing is, I bought the car as a dealer demo car with around 5k miles on it and it has never had any work done other than CAI, catch can and brake pads (all installed personally by me). It has always had a slight intermittent miss at idle which I chalked up to being the typical 6.2 idle lope.

Maybe the trip down the BOD & TOD at the end of June shook it loose,

They are trying to get $400 out of me for diagnostics and 1 plug and wire when the car is covered by the GM platinum protection plan, which is exclusionary and does NOT exclude spark plugs and wires. They played dumb until I offered to provide the contract number, then, mysteriously, should not need it, it should be in the system. They will likely not approve, but we will call them for approval and let you know.

Guess there is validity to their nickname "stealer".

The car is back from the dealer and all fixed. The root cause was a faulty spark plug wire, which in turn caused a fouled spark plug.
The retainer in the plug wire at the plug end was defective, which permitted to plug wire spring to press the plug wire off the plug, causing intermittent continuity with the spark plug and thus the misfire.

302SS did you get your issue resolved?

[mstgeer]

Originally Posted by KingLT1

Dealership isn't going to cover a car that has an aftermarket cam/valvetrain. You would be better off taking it to a reputable performance shop.

I'm not the OP, My car is 99% stock. My car was having a similar issue so i just piggy backed onto 302SS's post rather than clutter the site by starting a new "misfire" string.

I did learn there are multiple versions of the GM platinum extended service agreements which are underwritten different companies (not GM) and they have significantly different excluded parts.