Misfire at high boost and after wot pull
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From: tulsa, ok
Misfire at high boost and after wot pull Hey guys I have a 2001 Silverado that is running an on3 7875 turbo with a .585/.585 cam. I have street tuned myself. It ran fine for a little while, but now if I do a wot pull up to 9psi the boost gauge flutters and after the pull there is an evident misfire until I let it cool off or free rev it in neutral for a few seconds. This truck has the d585 coils with like 230,000 on them. Is it possible I have a bad coil at high load? Or is there anything else I should check. New ngk tr6 plugs gapped at .025, with new wires. Vcm scanner shows good timing and afr but after the pull it stays rich when misfiring. Tia
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From: tulsa, ok
.660 lift dual valvesprings and ls7 lifters installed 3k miles ago
It ran fine a few weeks ago when I was doing pulls, but I noticed it was 49 degrees then and it is now 79 out. I suspect coils, just checked the plugs and nothing out of the norm on any of them. I am running the factory thermostat. Wondering if I should step down to a 160 and adjust efans to lower temp. The entire hotside is wrapped and glows underneath after a pull. Iat's only in the mid 120s During the pull though.
It ran fine a few weeks ago when I was doing pulls, but I noticed it was 49 degrees then and it is now 79 out. I suspect coils, just checked the plugs and nothing out of the norm on any of them. I am running the factory thermostat. Wondering if I should step down to a 160 and adjust efans to lower temp. The entire hotside is wrapped and glows underneath after a pull. Iat's only in the mid 120s During the pull though.
Last edited by bbowerman; May 20, 2018 at 07:32 PM.
Sure you don't have something else going on? Something adding fuel at a certain temp or something in the tune? I've never seen a misfire show rich they always show lean spikes. Post up your tune and data log so we can take a look.
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From: Norn Iron
Hey guys I have a 2001 Silverado that is running an on3 7875 turbo with a .585/.585 cam. I have street tuned myself. It ran fine for a little while, but now if I do a wot pull up to 9psi the boost gauge flutters and after the pull there is an evident misfire until I let it cool off or free rev it in neutral for a few seconds. This truck has the d585 coils with like 230,000 on them. Is it possible I have a bad coil at high load? Or is there anything else I should check. New ngk tr6 plugs gapped at .025, with new wires. Vcm scanner shows good timing and afr but after the pull it stays rich when misfiring. Tia
Is the problem rpm or boost dependant ?
What are AFR's like on both banks, prior to and when the problem occurs ? Almost sounds like you could be dumping in far too much fuel.
Highly unlikely coils are the problem.
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From: tulsa, ok
Now it does it with any boost at all matter of fact it started acting up as soon as it hits around 100kpa. Sounded like a dead misfire, barely idled. So I pulled the wires while it idled and every one is hitting. Free rev it in neutral afterwards for a few seconds and it idled fine, or kill it wait 1-2 mins and start it back it's fine. Definitely sounds electrical. I did notice my control module voltage lower than usual 13.4 volts at idle or driving and I just changed this alternator right before the issue occured. No codes other than MAF but that's because it's failed for SD would a Bad alternator or battery cause this only at boost?
Last edited by bbowerman; May 22, 2018 at 07:20 PM.
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From: tulsa, ok
9psi is very low boost....so what do you mean by high boost ?
Is the problem rpm or boost dependant ?
What are AFR's like on both banks, prior to and when the problem occurs ? Almost sounds like you could be dumping in far too much fuel.
Highly unlikely coils are the problem.
Is the problem rpm or boost dependant ?
What are AFR's like on both banks, prior to and when the problem occurs ? Almost sounds like you could be dumping in far too much fuel.
Highly unlikely coils are the problem.
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From: Norn Iron
So everything was fine until you changed the alternator ?
Why did you change the alternator ?
And is voltage stable under load or at higher rpm when this is occuring ?
And AFR looks great ? Doesnt really mean a lot.
Why did you change the alternator ?
And is voltage stable under load or at higher rpm when this is occuring ?
And AFR looks great ? Doesnt really mean a lot.
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From: tulsa, ok
Went efans so I installed a 130amp instead of stock 105 amp. Afr was high 11s under boost I've tried adding and subtracting a little fuel with no luck. The vcm scans show nothing crazy except it idles at 84kpa when missing and 70 when it runs fine. But I believe that's due to the missfire. I am going to test the battery and alternator now to rule that out. Voltage is stable just lower than I'm used to seeing
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From: tulsa, ok
A few weeks back it ran fine must have done 8-9 pulls no issue. I have changed the tune since then but I tried going back to the old and the issue still existed.
Battery and alternator tested good tested them both 3 times... Still waiting on my new coils ups is taking forever. This has me lost. I can get a vcm log tomorrow blew a brake line...
Battery and alternator tested good tested them both 3 times... Still waiting on my new coils ups is taking forever. This has me lost. I can get a vcm log tomorrow blew a brake line...
Last edited by bbowerman; May 22, 2018 at 10:55 PM.
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From: Norn Iron
So you're now saying it also misfires at idle, not just under load ?
Sounds like a valvetrain or intake leak problem. That idle kpa reading under any circumstances is very high ( ie poor ) unless your cam has a lot of overlap or something
Did you touch or disturb anything around the intake during the works ?
Less likely is a bad earth or something
Sounds like a valvetrain or intake leak problem. That idle kpa reading under any circumstances is very high ( ie poor ) unless your cam has a lot of overlap or something
Did you touch or disturb anything around the intake during the works ?
Less likely is a bad earth or something
Thread Starter
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From: tulsa, ok
I found the issue last night. Changed the one suspected bad coil still didn't fix It would misfire as soon as boost came in and wouldn't stop missing until free revved or restarted. There is one table in hptuners I changed on the old tune and the new tune trying to solve another issue and I forgot about it, so I changed it back to the stock tunes settings and it fixed it all. Makes absolutely no sense to me how this table could cause this issue but I seen on hptuners forum some where having worse issues than I was. I only did one pull and it did not act up.
Airflow>Electronic Throttle>Desired Throttle Area
That was the culprit. This truck doesn't have electronic throttle but that one setting made it act really weird. Maybe someone will have a better explanation as to why it caused this.
Airflow>Electronic Throttle>Desired Throttle Area
That was the culprit. This truck doesn't have electronic throttle but that one setting made it act really weird. Maybe someone will have a better explanation as to why it caused this.
Last edited by bbowerman; May 23, 2018 at 07:30 AM.
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I found the issue last night. Changed the one suspected bad coil still didn't fix It would misfire as soon as boost came in and wouldn't stop missing until free revved or restarted. There is one table in hptuners I changed on the old tune and the new tune trying to solve another issue and I forgot about it, so I changed it back to the stock tunes settings and it fixed it all. Makes absolutely no sense to me how this table could cause this issue but I seen on hptuners forum some where having worse issues than I was. I only did one pull and it did not act up.
Airflow>Electronic Throttle>Desired Throttle Area
That was the culprit. This truck doesn't have electronic throttle but that one setting made it act really weird. Maybe someone will have a better explanation as to why it caused this.
Airflow>Electronic Throttle>Desired Throttle Area
That was the culprit. This truck doesn't have electronic throttle but that one setting made it act really weird. Maybe someone will have a better explanation as to why it caused this.
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From: tulsa, ok
It was a hard issue to explain without someone actually riding along the vcm scans looked good enough it just wasn't making sense. Yesterday before fixing this I was in open loop and it the afr randomly went super rich cruising at 65 (high10-low11). It was inconsistent every time I drove it the issue would happen somewhere else in the map. Usually only when boost started. Oh well at least it was rich instead of lean. I'm real skeptical of removing fuel when it ran just fine on that same fueling not long ago. Anyways thanks for the help!
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From: tulsa, ok
So I'm not sure what was going on the other day but the problem is back.....brand new set of coils and plugs gapped at .025 exact same issue. It will make a pull all the way up to peak boost. The pull feels good but I still think it should have more than what it's got. After the pull it is rich everywhere even in places it was just fine in earlier and has what feels like a dead misfire. if someone can't pinpoint this issue I'm about to start parting it out at this point. Bad map? Bad turbo? I'm lost