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Thread: HUMMER H2 Misfire

  1. #1
    Tuner in Training
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    HUMMER H2 Misfire

    Hello Everyone, I have an issue with my H2 for the past 3 years.

    On a cold start its smooth and perfect but when the engine temp. goes above 95c a random misfire starts on idle, no other issues at all.

    Previously i had a short in the engine harness causing the engine to stall under random conditions. i got this sorted out and the vehicle doesn't stall anymore and works normally except for the misfire which can be felt when engine shakes.

    Before knowing that there is a short in the harness i have replcaed the following parts with new ones:

    1- MAF
    2- Alternator
    3- Fuel Pump (3 Times)
    4- Fuel Pedal assembly
    5- Throttle Body and gasket
    6- ECU
    7- Crankshaft sensor
    8- Spark Plugs and Wires
    9- Two coils
    10- A\C clutch
    11- MAP
    12- Manifold gasket
    13- Fixed Hydrolic steering oil leakage
    14- Intake filter with heat resistant straight tube

    After fixing the short i replaced the following:

    1- MAF
    2- Battery
    3- Cleaned Grounds
    4- ECU with stock tune
    5- A\C internal fan
    6- A\C fan controller
    7- Tranny filter and gasket
    8- Tranny cooler

    and nothing has changed, it still misfires and shakes on idle.

    Note: I live in the middle east in one of the highest temp countries in the world(Kuwait).

    I have ran some scans but due to my limited knoweledge i have no idea what is wrong.

    Your help is highly appreciated.

    Thanks.8Aug2020 5PM Hummer H2 Log.hpl9Aug2020 Humer H2 730PM.hpl9Aug2020 Humer H2 815PM.hpl9Aug2020 Humer H2 820PM.hpl

  2. #2
    Tuning Addict 5FDP's Avatar
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    What plug gap are you running?

    Is there any way to lower those intake temps, it surely isn't good to see 180-190F degree intake temps. I know it's very hot there but even if it was 10-20 degrees over ambient that would be better.

    What about upping the rpm at idle by 100-150rpm?

    And how come you aren't running o2 sensors?? It's hard to know what the fueling is like at idle when it misfires without those or a wideband o2 sensor in the logs.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  3. #3
    Tuner in Training
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    Quote Originally Posted by 5FDP View Post
    What plug gap are you running?

    Is there any way to lower those intake temps, it surely isn't good to see 180-190F degree intake temps. I know it's very hot there but even if it was 10-20 degrees over ambient that would be better.

    What about upping the rpm at idle by 100-150rpm?

    And how come you aren't running o2 sensors?? It's hard to know what the fueling is like at idle when it misfires without those or a wideband o2 sensor in the logs.
    Thank you for your reply.

    I have no idea about plug gap, how to check on that?

    Regarding the O2 sensors, all of the 4 are disconnected and I have used the following to disable in ecu:

    Engine > Fuel > COT, Lean Cruise
    COT: set to "Disabled"

    Engine Diag > DTC's
    P0137: uncheck "SES Enable", set to "3 No error reported"
    P0138: uncheck "SES Enable", set to "3 No error reported"
    P0140: uncheck "SES Enable", set to "3 No error reported"
    P0141: uncheck "SES Enable", set to "3 No error reported"
    Po157: uncheck "SES Enable", set to "3 No error reported"
    P0157: uncheck "SES Enable", set to "3 No error reported"
    P0158: uncheck "SES Enable", set to "3 No error reported"
    P0160: uncheck "SES Enable", set to "3 No error reported"
    P0161: uncheck "SES Enable", set to "3 No error reported"
    P0420: uncheck "SES Enable", set to "3 No error reported"
    P0430: uncheck "SES Enable", set to "3 No error reported"

    If you need any specific reading please let me know

    Thanks again for your support

  4. #4
    Tuning Addict 5FDP's Avatar
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    A large plug gap could cause misfire. It should be around a .040 when you check the spark plugs with a gap tool.

    Is there a reason you are running open loop without o2 sensors??

    Without o2 sensors you'd have to be using a wideband o2 sensor in the exhaust to make sure the air fuel ratio's are staying okay.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  5. #5
    Tuner in Training
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    Quote Originally Posted by 5FDP View Post
    A large plug gap could cause misfire. It should be around a .040 when you check the spark plugs with a gap tool.

    Is there a reason you are running open loop without o2 sensors??

    Without o2 sensors you'd have to be using a wideband o2 sensor in the exhaust to make sure the air fuel ratio's are staying okay.
    Quote Originally Posted by 5FDP View Post
    A large plug gap could cause misfire. It should be around a .040 when you check the spark plugs with a gap tool.

    Is there a reason you are running open loop without o2 sensors??

    Without o2 sensors you'd have to be using a wideband o2 sensor in the exhaust to make sure the air fuel ratio's are staying okay.
    Thanks again for your reply.

    I should get the gap tool.

    I disabled the Pre Cat O2 sensors because at the time of having the short causing the engine to stall a technician thought that they are causing the stalling so we just unplugged the 2 pre-cat sensors and because I deleted the cats I also unplugged the 2 post cat sensors

    I have plugged the pre-cat sensors again after seeing your post and once the car warmed up I started getting hesitation on acceleration, almost stalling, the car shakes and I can see the front lights and dashboard lights flickering, after turning off the engine for like 40 minutes it started up normally then after driving a bit it started shaking again.

    Do you think I shall unplug them again? purchase new ones? or there might be an issue with their wiring? if there are any specific readings that can help, please let me know so I scan it with VCM but I don't know which channels exactly I shall add in VCM scanner.

    I appreciate your support.