[TAGZO]

I all,

I need some help with figuring out what is causing a random misfire at idle and slow driving (between 2 to 20 misfire count) and huge miss sometimes (200 misfire count)!.

Mods
2016 CTSV, headers with cats, roto fab big gulp, 103 TB, ported blower, upper and lower pulleys (~15 PSi), meth, chiller, 160 stat, catch can.

I took it to the dyno, and all is fine with an excellent number ~735 rwhp and the same TQ. It ran at the track; 1 and 2 runs were ok, 3rd run was horrible with ~200 misfires. And a drop of 1 sec in 1/4.

I changed the sparkplugs three times with different gapping (40,32,28), although they were fine. I checked the wires, and they were ok. I tested coils, and they were fine. I Did a leak down test, and all was fine; I took it to the dyno and made 750 rwhp and about the same TQ.. !?!?!?!?

I took it to the track; 1st and 2nd runs were ok. The same thing happened after a cooldown on the 3rd run, misfiring like crazy (in ~200 range).

Yesterday, the same type of misfire (~200) happed at 30kph cursing. It gradually faded when I leaned it to the paddle, slowed down and leaned on it smoothly, and slowly returned to the usual misfire of (~2 to 20 while driving).

I am getting confused. I don't know, but I thought VVT had a problem or DOD. maybe even the O2s are half-broken. I am unsure of what the problem is.

Can anyone help me out?
Note: all misfires mentioned here are from my aeroforce gauge pod.

I have logs if anyone is interested to have a look.

Cheers!

 

[07GTS]

are they actual misfires u can feel from the engine or is it just the ecu logging misfires ?

 

[Schulminator]

Injector related misfire most likely.

 

[BanditV]

Replace wires. Too many times mine and looked fine and caused me hours of chasing and trying. If you changed plugs, I'd start wires next. I chased one on my LSA TA build two weeks ago. Put it away for the winter, ran great. Took it down for summer, misfire at idle, like backfire miss. Less than 1000miles on plugs and wires. Sent injectors out and had cleaned/balanced, changed plugs, checked coils, fuel filters, screwed with tune endlessly. Wires looked perfect. Changed wires....fixed. Weeks and several $100 later..

 

[TAGZO]

are they actual misfires u can feel from the engine or is it just the ecu logging misfires ?

you surely can feel it. it is just random. sometimes more, sometimes less.

 

[TAGZO]

I have noticed! When I first start the car in the morning, there is no misfire or has a smoother idle for 10 seconds!? could it be O2 related? (open-close loop).

The car drives ok, but you can feel the misfire if it jumps to 10-20 on my aeroforce gauge. I hate replacing things that I don't need to replace. But I guess I will replace the spark wires, although they tested fine at the dealer.

 

[specialp]

Do you have larger injectors? If so and the misfires are at low fueling crusing like the 30kph you said it is probably short pulse fueling issues. Big injectors are bad at low fuel requirements (think about filling a glass accurately with a full blast garden hose) 200 is too high but you will likely always have some sporadic misfires. I would try checking proportional fueling in HP tuners and tune that. you need to lower the amplitude of fuel adjustments. What happens is sometimes it requests so little fuel your injector might not fire at all. Log average pulse width too.

 

[07GTS]

I have noticed! When I first start the car in the morning, there is no misfire or has a smoother idle for 10 seconds!? could it be O2 related? (open-close loop).

The car drives ok, but you can feel the misfire if it jumps to 10-20 on my aeroforce gauge. I hate replacing things that I don't need to replace. But I guess I will replace the spark wires, although they tested fine at the dealer.

jumps 10-20 is that spark deg ? or AFR ?

 

[NoahsG2V]

The 2016 is the direct injection engine rite? On the GM trucks anyway there seems to be a carbon buildup issue on the valves and on the injectors themselves. Do you ha e the ability to do an injector balance test?(can be done with a snap on solus scanner) if one of them is stuck open or is hesitant it will show itself on that test.

 

[TAGZO]

jumps 10-20 is that spark deg ? or AFR ?

That is a misfire count by aeroforce gauge. and it is a total count

 

[07GTS]

That is a misfire count by aeroforce gauge. and it is a total count

ok, what are the 02's showing before/during the misfires ? is it always same cylinder/cylinders ? if so if u swap coils/leads/plugs around does it change with them or stay on same cylinders ? if u have log in hpt if u can post it up can have a look

 

[kittyboy]

Log the individual cylinder misfires in HPtuner, timing, air/fuel, fuel pressure, injector data, might help. Good luck trouble shooting.

 

[TAGZO]

I do have logs already. It is a random misfire on cruising. However, at the track run misfire, it was number 8. I changed the coil and nothing changed

Does anyone want to have a look at the log files?