Results 1 to 7 of 7

Thread: Reading misfires

  1. #1
    Tuner
    Join Date
    Jan 2019
    Location
    North Carolina
    Posts
    54

    Reading misfires

    I am currently logging Misfire current cylinders 1-8 as well as total misfires. I attached my log and can see where the misfire count goes up occasionally but cant tell if its normal or not. I feel like I can feel a slight misfire at low rpm under partial load, but not sure how to confirm that. Anyone have any insight as to weather this is normal or something I need to dig deeper into?

    Thanks
    Attached Files Attached Files

  2. #2
    For the misfire you are describing and the log shows, I would pull the #1 plug and inspect it for abnormalities. I'm not there to feel it, but your description makes it seem like a bit of rough running, then ok again.
    03 Z06 stock.......for now
    05 Siearra 5.3 daily
    I have realized that tuning is a rabbit hole. No problem diving down this hole, in fact I jumped willingly. Just want to avoid hitting every ugly rock or root on the way down it.

  3. #3
    Tuner
    Join Date
    Jan 2019
    Location
    North Carolina
    Posts
    54
    I actually went digging and found that #1 Cyl plug wire wasn't fully seat went and did a drive this morning and it still was showing a bunch of misfires under the history for #1 ( a lot more than the others) however as I was driving down the road the SES light came on for a Knock sensor code (something to do with the wiring) I cleared the codes which also cleared the misfire history and driving down the road it wasnt registering any misfires, only at idle. Its still higher than the others but not sure if this is normal? I have a btr stage 2 truck cam so the cam is 212/218 on 111 lobe separation. Attached is the log file from this morning and my most recent tune. AFR's seem to be ok for me for now and the only real issue I am having is hanging idle when i let off the gas and I am driving.
    Attached Files Attached Files

  4. #4
    History misfires don't clear for awhile, or until codes are cleared. As for the knock sensor, those are some of the most common issues with the gen3 engines. My sierra has had the CEL on for knock sensors for a couple years. Is a daily driver no mods so I don't care as of yet. If one of the sensors is bad, do yourself a favor and change both of them along with the KS sub-harness. KS#2(rear one) is most common for failure due to water contamination. GM had a bulletin out years ago directing to make a V shaped dam with silicone to route the water away from the rear sensor to help prevent this. I usually still do this when I get a gen3 with KS issues. Maybe I should fix my own someday....

    Misfires at idle could be a number of things. Watching the log it is not adding the misfires to history counters, so I would not pursue that unless you can feel them or it is hurting performance. Unless of course you have nothing better to do....lol. If it won't log them to history, it most likely won't set a P0300/CEL.

    Is it a DBW or DBC setup for the throttle? Either way, might try a search for hanging throttle. Haven't gotten into too much of that yet, still learning.
    03 Z06 stock.......for now
    05 Siearra 5.3 daily
    I have realized that tuning is a rabbit hole. No problem diving down this hole, in fact I jumped willingly. Just want to avoid hitting every ugly rock or root on the way down it.

  5. #5
    Tuner
    Join Date
    Jan 2019
    Location
    North Carolina
    Posts
    54
    Quote Originally Posted by vettemakesemwet View Post
    History misfires don't clear for awhile, or until codes are cleared. As for the knock sensor, those are some of the most common issues with the gen3 engines. My sierra has had the CEL on for knock sensors for a couple years. Is a daily driver no mods so I don't care as of yet. If one of the sensors is bad, do yourself a favor and change both of them along with the KS sub-harness. KS#2(rear one) is most common for failure due to water contamination. GM had a bulletin out years ago directing to make a V shaped dam with silicone to route the water away from the rear sensor to help prevent this. I usually still do this when I get a gen3 with KS issues. Maybe I should fix my own someday....

    Misfires at idle could be a number of things. Watching the log it is not adding the misfires to history counters, so I would not pursue that unless you can feel them or it is hurting performance. Unless of course you have nothing better to do....lol. If it won't log them to history, it most likely won't set a P0300/CEL.

    Is it a DBW or DBC setup for the throttle? Either way, might try a search for hanging throttle. Haven't gotten into too much of that yet, still learning.
    I think I have the misfires figured out, I think I am just being hyper sensitive since its a new motor. I actually replaced the knock sensor wiring harness and the sensors, I think this was just a weird thing that happened. I did build the silicone dam around the rear one as well.
    I have a DBC setup and actually I though the Throttle cracker didn't effect the DBC setups but i disabled the Throttle cracker and it is LOADS better.

  6. #6
    Be hyper sensitive. Most people don't blow up engines while tuning when they pay attention. Not sure about the throttle cracker, still learning about that. Glad you got it sorted.
    03 Z06 stock.......for now
    05 Siearra 5.3 daily
    I have realized that tuning is a rabbit hole. No problem diving down this hole, in fact I jumped willingly. Just want to avoid hitting every ugly rock or root on the way down it.

  7. #7
    Advanced Tuner
    Join Date
    Mar 2011
    Posts
    321
    You haven't desensitized the misfire tables at all. They are still stock. Anytime you install a decent size cam you have to do that in order to prevent having false misfires present.
    There are also several other areas where you can make substantial improvements.
    Reduce the PE delay rpm and Enable torque and TPS thresholds. Increase the enrichment Ramp In Rate.
    Reduce or remove transmission TM.
    Increase shift points and rev limiter.
    Add a couple degrees of ignition timing.