Misfires

I've never logged misfires before and I'm not familiar with the terminology, such as "mode index". So I'm very much a newbie as far as misfire logging is concerned.

I logged them tonight to see if this was the reason I would occasionally lose TCC lockup. I think it is the reason. Near frame 4375, cylinder #7 logged quite a few misfires. Shortly thereafter, I lost TCC lockup. Later, I cleared DTC's (even though none were logged according to the HPT scanner), and TCC lockup started working again.

My main concern however is that I see many more misfire counts on cylinder #7 than any other cylinder.

What's the first thing to check? Plug wire? Plug? Injector? Coil? Swap these one at a time with another cylinder and see if the misfires move to that cylinder?

What would be considered a normal misfire count?

I have an LS2 with LS9 cam, LSA heads, Circle-D 4l80e converter (low stall).

Thanks

Quote:

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Originally Posted by GNXClone

What's the first thing to check? Plug wire? Plug? Injector? Coil? Swap these one at a time with another cylinder and see if the misfires move to that cylinder?

What would be considered a normal misfire count?

I have an LS2 with LS9 cam, LSA heads, Circle-D 4l80e converter (low stall).

Thanks

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Sir I like the way you think! Like a mechanic. Move parts around and see if issue follows to narrow down problem. SMART man!

I believe in the end you may find your issue is in your tune for the aftermarket converter (forum monkey guess mind you).

POST TUNE

don't put your mechanic hat away just yet either...

Normal misfire count is 0. Misfires are NOT normal nor in my opinion acceptable unless you thrive on frequent catastrophe.

Why does misfire total go to 30 and then reset to 0 by the end of the scan? I'm using beta scanner, dunno if that matters.

I had the same issue whenI had my Yank 3600 put in. I had to double the misfire table to get the lockup right. It is common to have to up the tables for higher stalls. Does it feel like its missing badly, or is it just the converter changing the crank harmonics so the computer thinks its misfiring.

Misfire counts reset after a certain period of time. I don't know exactly how it works but the misfire count is a total count over the last X seconds.

I don't feel the misfires at all, and it doesn't break up under boost, so its not a huge issue. But since I have read many threads on how misfire readings due to a cam or converter change can cause the TCC to not lockup, I knew to log them. I'm not too concerned with the lockup issue as I know the fix is to raise the values in the misfire tables or max them out. The logging was mainly to verify the misfire count as the cause, and to familiarize myself with misfire logging capability in case I need to use it in the future to track a misfire I can feel.

The concern I have now though is that cylinder #7 has far more misfire counts than the others, so I definitely feel the need to diagnose that.

I wish I knew how the misfire tables worked so I could understand what raising these values is really doing.

Nice to know there was an answer to the kr reset question. I've heard of the doubling feature to eliminate the kr. Concerning the #7 all I can think of is its due to the converter being flower to that piston. Update tune and report back.

I just swapped the #7 spark plug with #1, both plugs looked fine. They are Delco 41-104 (stock ZR1/CTSV) gapped at .40")
Swapped #7 plug wire with #3
Swapped #7 coil with #5

I'm not swapping the injector yet until I see if this is electrical. No reason to spill the rail fuel if I don't need to.

I don't want to raise the misfire table values just yet, in case that will mask out the misfires.

Getting ready to take it for a spin and see what happens. I hope I see the misfire move to #1, #3 or #5.

Misfires are still much higher in #7. So that eliminates the coil, plug or plug wire as the culprit.

Guess I'll try swapping injectors tomorrow.

Something just occurred to me. This is a new engine, and I haven't performed a CASE learn yet. I wonder if this plays into the misfire detection?

I'm guessing that the ECM reads the crank angle and watches the acceleration of the crank on each cylinder firing.

Although I would think this would spread the misfires equally amongst the cylinders...but who knows...

You're right in how the ECM interprets a misfire. I would tend to agree that if it were a CASE learn issue, it wouldn't isolate to one cylinder. I'll be curious to see what happens after swapping injectors.

could it be the weights on the flywheel/flex plate or how the torque converter is balance that one clyinder may show more then others?

I considered that...could be I suppose. I do have a CAT power flex plate, not stock.

Any update? Im curious how this ended up.

No updates yet. I haven't taken the time to swap injectors around. Maybe today if I get some motivation. :)

Dang I am chasing a similar #7 misfire, new plugs wires and swapped coil packs but no change. Thinking injectors or possible intake manifold leak?

@allgo - get a hollow tube (tranny line works well & bends easy) and listen around for leaks. If you dont find one, swap the injector. I would also do a compression test. Dont rule out a bad connection in the injector harness/clip or coil pack connector. Check the coil connector for moisture too. Someone on the SS forum had water get in one of the connectors due to a bad seal. Thats all I can think of for now.

Wonder how OP is doing.....

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Originally Posted by gn2beatu

Wonder how OP is doing.....

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Because I could never feel or hear the misfire, I've disabled misfire detection in the tune. I did this so the TCC would stay locked up.

Sort of like torque management...I just got rid of it altogether.

Quote:

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Originally Posted by gn2beatu

@allgo - get a hollow tube (tranny line works well & bends easy) and listen around for leaks. If you dont find one, swap the injector. I would also do a compression test. Dont rule out a bad connection in the injector harness/clip or coil pack connector. Check the coil connector for moisture too. Someone on the SS forum had water get in one of the connectors due to a bad seal. Thats all I can think of for now.

Wonder how OP is doing.....

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Well sprayed some carb cleaner around the intake to see if I could notice anything, nothing. Couldn't find a good listening piece but I will find something. Put the new K&N on as well as pulled the fuel pump to do the fuel level sensor and found both strainers clogged full of crap so I replaced both of those as well. Truck is running much better, more power, not nearly as many misfires but still get some misfires as well as the ECM retarding the timing.

I need lots of assistance. My mechanic switched out my prior cam to a H2c livernois cam in my g8. The heads did not come off in this switch.

Right after the switch I have noticed a miss/slip at 5200 to 5400 in first gear and then when it hits second the same thing happens at the same rpm. This is only at wot.

I have a yank 3600 stall, gmpp heads, the cam i just mentioned, an underdrive pulley, rotofab, ported t.b. and intake, 1 7/8s kooks mids with cats.

I checked the wires and even replaced them with an old set in the garage. The plugs only have around 5K on them. 5ix.

I also scanned for timing and cylinder efficiency. I used to get .84 to .88. Now the most I get is .76. So something is wrong.

The mechanic did say he had a hell of a time removing the underdrive pulley. But I was told even if there was some damage to that it would not cause the problem. But I read else where it can.

1) I do not know how to scan for misfires. I think my tuner turned off misfires when the first hipo cam went in. So where do I turn it back on? In the engine diagnostics? And then is there a table in hp tuners that can log misfires? If so where do I find it? If not how would I download it?

This is very frustrating. Any assistance would be appreciated.

Do misfires show when in SD? E38

well, from my little knowledge u should re-tune your PCM for the new Cam swap and the changes on cylinder eff. is normal due to the changes on the cam lobe size.

and for logging the misfire just open ur HPT scanner make sure u Inser to the Table display Misfire current cylinder or History cylinder by right click on n empty space in the table > Insert > PID List > Engine Diagnostics > Misfire , Then fill the empty spaces with all cylinders # u wanna log either current or history.

i guess that would make it certin if you have a misfire or not.

please senior's correct me if i am wrong