Need help with misfire

[angrygoat]

I have been chasing misfires for a couple of weeks on a friend's 06 GTO. The mods are 228/238 cam, PRC 243 heads, Kooks 1 3/4 LTs, Corsa, FMS green tops, vic jr, edelbrock elbow and vara-ram. He also recently went with a Spec 3 and aluminum flywheel.

The symptom is misfires predominately on cyl 5 and 6. As much at 2500+ depending on how long I drive it, where as the other cylinders are anywhere from 0-15. The weird thing is it only misfires above 2k rpms. I can drive all day under 2k but as soon as I cruise over 2k the misfires rack up.

We have switch coils, switched plug wires, gapped and regapped the plugs, injectors are 2 wks old. I have been adjusting the timing back and forth in the 2k to 2400 rpm cells with no improvement. I was thinking the timing was too far retarded and causing the misfire. I have looked over the CPS wiring and found nothing.

I have attached the tune, and logs. The only thing I have left to check is two swap injectors around and see if they problem follows the injector. The other thing I was thinking is the aluminum flywheel is throwing everything off

[bluegoat06]

I think there is a lot more to change in those injector settings rather than injector flow rate vs kpa alone. once you do that, Re-adjust VE, then MAF, then see if you can replicate the issue. you can also try to max out all the misfires tables, but then, you injector settings are still messed up to begin with , so you'll be covering what could be the root cause of the problem. just a thought.

[angrygoat]

Damn it, you know it never fails. Just when you think you have a small clue of what you are doing with this stuff, you forget something so basic it makes you feel stupid all over again

[angrygoat]

ok, so I went on a search to find the green top data. I printed it off of some website and it says the min pulsewidth is 1.13 at 39.15 psi. Does this need to be converted to be used with GM's 58psi? I also found the offset values but as usual the tables dont match to what is in HPtuners. The GM table is more of a 3-D whereas the Ford offset voltage table is linear.

[DSteck]

ok, so I went on a search to find the green top data. I printed it off of some website and it says the min pulsewidth is 1.13 at 39.15 psi. Does this need to be converted to be used with GM's 58psi? I also found the offset values but as usual the tables dont match to what is in HPtuners. The GM table is more of a 3-D whereas the Ford offset voltage table is linear.

If you purchase Greg Banish's DVD, it has the full calibration data for those injectors.

[madvette08]

I would not look at the injectors programing, im not saying the injectors are physically bad im just saying not to look at the tune yet, and in stead look for a physical problem.

Ian

[EFI]

As much at 2500+ depending on how long I drive it, where as the other cylinders are anywhere from 0-15. The weird thing is it only misfires above 2k rpms. I can drive all day under 2k but as soon as I cruise over 2k the misfires rack up

What is your misfire count climb to in one cycle (not the total historical count, but the current count)on the normal cylinders vs 5 and 6?

[angrygoat]

Yeah I finally broke down and ordered the DVD. I hope there is more info in there than just injector values. We'll see

I have checked everything mechanical I have thought of, esp with it only being on two cylinder. Rockers are tight, pushrods are straight and good compression, different coils, plugs and wires.

EFI, do you mean the current misfire? I have seen where the history seems to reset sometimes and start over. Im assuming thats one cycle. Could you explain a little more for me? Thanks

[EFI]

Well you have 2 misfire PIDs: one is the current misfire count, the other is a total historical misfire count.

Eg: current misfire count goes to 20 then resets, then 2 minutes later goes to 20 and resets again. It does that 3 more times during the log. The current misfire is a max of 20, but a historical count will show 100 (but that doesn't mean it missed 100 times in the current cycle, it means it missed 100 times total over the span of the scan...could have been 2 counts 50 times)

So is that 2500+ count a historic, as in it keeps adding and adding all the misfires over the lifetime of the scan, or is the current count actually go up to 2500?

I'm asking this because I have the same problem on one cylinder...but mine goes up to a max of 14-16 then resets back to 0. A few minutes later it starts up again and goes anywhere from 2-16 and resets again.

Over the span of a 20 minute log, the total count is in the thousands...but each time it doesn't go higher than 18.

[angrygoat]

I will check that out. Thank you

[RWTD]

Swap the injectors with two from known cylinders that are not misfiring, and see what happens there.

Also, any particular reason you're attempting to run the misfire test with a cam? I'm not saying you can't, but generally you'll get misfires.

[bluegoat06]

RWTD, how do you run the misfire test ?

I don't have misfires, i haven't touched the misfires tables at all, or disabled diagnostic tests, and i don't get misfires at all, granted, my cam is smaller.

[RWTD]

When I say "run the misfire test", I meant it just operating in general.

[angrygoat]

Swap the injectors with two from known cylinders that are not misfiring, and see what happens there.

Also, any particular reason you're attempting to run the misfire test with a cam? I'm not saying you can't, but generally you'll get misfires.

Thats what I was thinking of doing. I thought you could keep the misfire but had to increase the misfire tables at idle where I thought you were most likely to get false misfires. I thought the cam would "stabilize" and you wouldn't get that false misfire above a certain rpm just off idle

[RWTD]

Thats what I was thinking of doing. I thought you could keep the misfire but had to increase the misfire tables at idle where I thought you were most likely to get false misfires. I thought the cam would "stabalize" and you wouldnt get that false misfire above a certain rpm just off idle

In some cases, you're exactly right, you can do that, but with some cams that isn't always possible.