missing under load, backfires, popping
04-24-2011, 05:52 PM
#31
If you're cammed, your tune won't count misfires(typically). You need to reflash it to count and log misfires, then it will. Then flash it back the other way after you get it fixed.
This is done this way to reduce check engine lights on cammed combos that aren't really misfiring.
This is done this way to reduce check engine lights on cammed combos that aren't really misfiring.
04-25-2011, 08:56 AM
#32
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If you're cammed, your tune won't count misfires(typically). You need to reflash it to count and log misfires, then it will. Then flash it back the other way after you get it fixed.
This is done this way to reduce check engine lights on cammed combos that aren't really misfiring.
This is done this way to reduce check engine lights on cammed combos that aren't really misfiring.
04-28-2011, 02:54 PM
#35
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UPDATE: Ok, i got nothing....lol
Leak down test got put on hold due to incorrect compressor fittings for the gauge and it was Easter sunday so this weekend will try again, but i'm not anticipating anything showing up in this test to indicate what my problem is. I'll be sending my injectors out to FIC to have them cleaned/checked after this weekend.
Leak down test got put on hold due to incorrect compressor fittings for the gauge and it was Easter sunday so this weekend will try again, but i'm not anticipating anything showing up in this test to indicate what my problem is. I'll be sending my injectors out to FIC to have them cleaned/checked after this weekend.
04-28-2011, 11:54 PM
#36
Don't send out your injectors. I'm convinced that your problem is secondary ignition. I've studied your tune and seen a couple things to point out to you.
Your tune is 2 bar speed density open loop. Your short term & long term fuel trims have been disabled. All of your O2 sensors have been tuned out. Yet, you mentioned replacing O2 sensors in a repair attempt. They didn't help because your PCM doesn't use them at all. The only sensors your PCM is still using are: MAP, ECT, TPS, IAT, CKP, CMP, and IAC. None of those would cause an issue like you describe if failing, without throwing codes.
Your PCM does have misfire diagnostics, but only limited misfire diagnostics. The only misfire related DTC it is capable of throwing is P0300, and the count has to be pretty high before it will throw the code. If you lower the counts needed to throw the code, it still won't help you determine which cylinder, because your PCM doesn't even have the ability for P0301, P0302, P0303, P0304, P0305, P0306, P0307, and P0308. If it did, you could lower the misfire counts required before setting the DTC, and then narrow down which cylinder the misfire is on. But for whatever reason, your PCM isn't set up for this. I've seen this before on HD truck PCM's and on a couple others, not quite sure what the reasoning is, but General Motors only needed misfire diagnostics to be on certain vehicles, not all of them.
The basics of your tune seem to be in good order. I didn't see anything out of whack that might cause you some type of driveability issues.
Your description of the problem, in your original post, is a classic "secondary ignition failure" description. Please revisit your ignition system. I had a LT1 Corvette in the shop today that another shop had for a year. They fixed some leaks, including a water pump, and also replaced the Opti-Spark system and did a tune up. After doing so, the engine ran rough & missed under light load. They couldn't figure it out, replaced the Opti-Spark & plug wires again, suspecting defective parts, no change. According to the car owner, they dicked around with the car for a year, then just gave it back to him. Told him to take it somewhere else, and call them & tell them what was wrong. After a couple of simple tests and checkouts, found the #6 spark plug cracked, and the #4 spark plug fouled. Replaced those 2 plugs with new, and it test drove great.
You've already checked alot of important things. Other common failures like cats, O2's, & MAF, you don't have. I think you need to go back & pull all of the spark plugs and wires and look them over really closely. Check to see if each plug wire snaps strongly onto the plug. Poor plug wire retention(loose on the plug OR coil) can cause your condition. Read each spark plug, look closely at each porcelain for cracking & carbon tracking, and ohm out each wire. Also, if you find a spark plug with a crack in the side, or carbon tracking in the side, replace that plug wire as well. Even if you can't see anything wrong with the wire, it will also have carbon tracking, and will cause problems for you.
I hope this helps you find your issue.
Your tune is 2 bar speed density open loop. Your short term & long term fuel trims have been disabled. All of your O2 sensors have been tuned out. Yet, you mentioned replacing O2 sensors in a repair attempt. They didn't help because your PCM doesn't use them at all. The only sensors your PCM is still using are: MAP, ECT, TPS, IAT, CKP, CMP, and IAC. None of those would cause an issue like you describe if failing, without throwing codes.
Your PCM does have misfire diagnostics, but only limited misfire diagnostics. The only misfire related DTC it is capable of throwing is P0300, and the count has to be pretty high before it will throw the code. If you lower the counts needed to throw the code, it still won't help you determine which cylinder, because your PCM doesn't even have the ability for P0301, P0302, P0303, P0304, P0305, P0306, P0307, and P0308. If it did, you could lower the misfire counts required before setting the DTC, and then narrow down which cylinder the misfire is on. But for whatever reason, your PCM isn't set up for this. I've seen this before on HD truck PCM's and on a couple others, not quite sure what the reasoning is, but General Motors only needed misfire diagnostics to be on certain vehicles, not all of them.
The basics of your tune seem to be in good order. I didn't see anything out of whack that might cause you some type of driveability issues.
Your description of the problem, in your original post, is a classic "secondary ignition failure" description. Please revisit your ignition system. I had a LT1 Corvette in the shop today that another shop had for a year. They fixed some leaks, including a water pump, and also replaced the Opti-Spark system and did a tune up. After doing so, the engine ran rough & missed under light load. They couldn't figure it out, replaced the Opti-Spark & plug wires again, suspecting defective parts, no change. According to the car owner, they dicked around with the car for a year, then just gave it back to him. Told him to take it somewhere else, and call them & tell them what was wrong. After a couple of simple tests and checkouts, found the #6 spark plug cracked, and the #4 spark plug fouled. Replaced those 2 plugs with new, and it test drove great.
You've already checked alot of important things. Other common failures like cats, O2's, & MAF, you don't have. I think you need to go back & pull all of the spark plugs and wires and look them over really closely. Check to see if each plug wire snaps strongly onto the plug. Poor plug wire retention(loose on the plug OR coil) can cause your condition. Read each spark plug, look closely at each porcelain for cracking & carbon tracking, and ohm out each wire. Also, if you find a spark plug with a crack in the side, or carbon tracking in the side, replace that plug wire as well. Even if you can't see anything wrong with the wire, it will also have carbon tracking, and will cause problems for you.
I hope this helps you find your issue.
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Ritchie B. Michael (03-27-2021)
04-29-2011, 11:50 AM
#37
Notorious BIG
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Roger,
First, thank you very much for taking the time to help me out.
The tune i sent you I forgot that i had disabled the STFT in OpenLoop. I did that to help diagnose my problem making sure my 02's were not the issue, even though i replaced them. The reason i replaced them was because normally I am using STFT's.
I had no idea that my pcm did not have full misfire diagnostics, that thought never crossed my mind at all. I never even thought to check to see if P030x codes were listed to even be enabled/disabled. They're not even there! I guess that explains why misfires are not throwing CEL's, HOWEVER it is strange though, because in the past, a few years ago, it did throw P0300. It was so long ago, i can't even remember what the cause or the fix was.
I'm glad you didn't see anything WAY out in left field with my tune, although i knew you wouldn't. I had a guy who really knows his stuff helping me out when I was doing a lot of tuning on it a couple years ago.
I just don't see how it could be plugs or wires as I have changed them both, twice now. Coils have been changed also.
You have definitely given me some good info and things to think about. I already have most everything disconnected and the blower ready to come off, i'm going to go ahead and send the injectors just to be thorough at this point. Its cheap insurance.
Thank you again for taking the time to try and help me out. It is greatly appreciated. I'll keep this thread updated with my findings.
First, thank you very much for taking the time to help me out.
The tune i sent you I forgot that i had disabled the STFT in OpenLoop. I did that to help diagnose my problem making sure my 02's were not the issue, even though i replaced them. The reason i replaced them was because normally I am using STFT's.
I had no idea that my pcm did not have full misfire diagnostics, that thought never crossed my mind at all. I never even thought to check to see if P030x codes were listed to even be enabled/disabled. They're not even there! I guess that explains why misfires are not throwing CEL's, HOWEVER it is strange though, because in the past, a few years ago, it did throw P0300. It was so long ago, i can't even remember what the cause or the fix was.
I'm glad you didn't see anything WAY out in left field with my tune, although i knew you wouldn't. I had a guy who really knows his stuff helping me out when I was doing a lot of tuning on it a couple years ago.
I just don't see how it could be plugs or wires as I have changed them both, twice now. Coils have been changed also.
You have definitely given me some good info and things to think about. I already have most everything disconnected and the blower ready to come off, i'm going to go ahead and send the injectors just to be thorough at this point. Its cheap insurance.
Thank you again for taking the time to try and help me out. It is greatly appreciated. I'll keep this thread updated with my findings.
04-29-2011, 02:03 PM
#38
Josh, did you run a misfire configuration to determine what cylinders are missing and how often? This could nail it rather quickly. If you need a configuration, shoot me an E-mail as .cfg files are not supported by this site.
You wouldn't happen to have P0200 disabled in your tune file would you? I had this disabled (by accident) and had a hell of a time chasing down a misfire after my 408 swap. Have you checked your injector harness splices??? A bad splice on any connector (should trip P0200) would cause your issues as each bank share a common wire.
You wouldn't happen to have P0200 disabled in your tune file would you? I had this disabled (by accident) and had a hell of a time chasing down a misfire after my 408 swap. Have you checked your injector harness splices??? A bad splice on any connector (should trip P0200) would cause your issues as each bank share a common wire.
04-29-2011, 02:32 PM
#39
Josh, did you run a misfire configuration to determine what cylinders are missing and how often? This could nail it rather quickly. If you need a configuration, shoot me an E-mail as .cfg files are not supported by this site.
You wouldn't happen to have P0200 disabled in your tune file would you? I had this disabled (by accident) and had a hell of a time chasing down a misfire after my 408 swap. Have you checked your injector harness splices??? A bad splice on any connector (should trip P0200) would cause your issues as each bank share a common wire.
You wouldn't happen to have P0200 disabled in your tune file would you? I had this disabled (by accident) and had a hell of a time chasing down a misfire after my 408 swap. Have you checked your injector harness splices??? A bad splice on any connector (should trip P0200) would cause your issues as each bank share a common wire.
05-09-2011, 10:30 AM
#40
Notorious BIG
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UPDATE, leak down test checked out, could not find any issues. Sent injectors to FIC to have them checked and serviced. Don't think i'm going to find anything out on the injectors and i'll be back at square one 