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  1. #1
    Chapter President

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    Need feedback.. rough idle and hesitation once engines is hot, no codes on DIC.

    Hopefully someone else has experienced this problem. I have a 2005 H2 SUT with 200,000 miles and over the past couple of months, I have noticed that there is slight hesitation on acceleration and the idle is very rough once the engine is hot or has been running for more than 30 mins. It feels almost like a misfire, but the DIC is not showing and codes and had a diagnostic done yesterday and it did not show any codes, and all sensors (i.e., O2, knock, etc.) were showing fine. The technician I spoke with is someone I trust and is a personal friend, he told me that it is most likely the timing chain, which may have stretched slightly and when the engine is cold the chain is tight enough not to notice the problem, but once the chain gets hot, it is possible that even some minor expansion could cause enough slack in the chain to throw of the timing. It seem logical, but I wanted to see if anyone had any other ideas before I go this route. For starters he suggested I put a wrench on the drive fan and try to turn the crank shaft to see if there is any noticeable movement or play when the engine is cold and to try this again when the engine is hot to see if it develops any play in the chain. Any thoughts you guys may have would be appreciated.
    B I G 2 D A B A N K

    2005 H2 SUT, Desert Sand

  2. #2
    "Like Nothing Else"
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    My first thought, before I read it, was the timing chain. Reason being at 200k miles it would make sense as a part to adjust or replace (not sure if you've done this or not). Just my .02
    -2009 H3 Alpha/Adv||SAS/SOA
    -2008 H3 Alpha-RIP

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    Big2dabank (12-16-2015)

  4. #3
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    I'm not going to say it's impossible that the chain stretches when it's hot, but it's impossible....

    That said, it could be one of the tensioners that causes the problem. What does the running graphs show while you're running? Is the EGTs getting too hot or too cold? how is the timing? you can record with HPTuners then play back what it is... since it's doing it often, you should be able to capture what the issue is. I had a similar issue with my H3, eventually I got the trouble code of the gas pedal and/or the throttle body. Until I got a code, it was pretty frustrating. I'm not suggesting replacing those parts - I'm simply saying that sometimes you have to wait it to throw a code (presuming you can't diagnose it with a running test).
    This too shall pass
    on a tow truck

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    Big2dabank (12-16-2015)

  6. #4
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    He didn't mean stretch in the conventional way, so I might have misstated that part. He meant that the pins in the chain become worn, thus creating slack, which could worsen as the engine heats up and why my problem is not noticeable when cold and only after it heats up. This one is certainly a little strange for me, I never had to deal with a timing chain issue before. We tried everything yesterday to try to get it to throw a code, and it never would, almost got it stall several times with a quick bump and release of the skinny pedal. I am going to let my friend drive it for the evening and data log it to see whats going on.
    B I G 2 D A B A N K

    2005 H2 SUT, Desert Sand

  7. #5
    Super Swamper
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    good luck, I can't imagine how the pins could wear - it's a roller set up - but stranger things have happened.
    This too shall pass
    on a tow truck

  8. #6
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    Don't know if this will help, but I thought it's worth a try:

    Document ID# 1527156 2003 HUMMER H2

    Idle Instability, Low or Rough Idle with Electronic Throttle Control (Clean Throttle Body) #04-06-04-040 - (06/14/2004)Idle Instability, Low or Rough Idle with Electronic Throttle Control (Clean Throttle Body)

    2002-2003 Cadillac Escalade, Escalade EXT
    2000-2003 Chevrolet Silverado, Suburban, Tahoe
    2002-2003 Chevrolet Avalanche
    2000-2003 GMC Sierra, Yukon, Yukon XL
    2003 Hummer H2

    with 4.8L, 5.3L or 6.0L V8 Engine (VINs V, T, Z, N, U - RPOs LR4, LM7, L59, LQ9, LQ4) and Electronic Throttle Control

    Condition

    Some owners may comment on an idle instability, low idle speed or rough idle.

    Cause

    Condition may be caused by deposits in the throttle body bore.

    Correction

    Clean throttle body bore and throttle valve plate of carbon using a shop rag and an appropriate cleaner. Refer to Engine Controls Repair Procedures - Throttle Body Cleaning Procedure. This procedure may be performed at any mileage necessary. Check to determine if the PCM calibration has been previously updated to one that includes the update for throttle body coking.
    DaveK
    K6DTK

  9. #7
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    I wish it was that easy, I clean the maf and throttle body about once a year.


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    B I G 2 D A B A N K

    2005 H2 SUT, Desert Sand

  10. #8
    Spilled Milk

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    Head gasket
    Quote Originally Posted by rascole View Post
    I'm pretty anal when it comes to poking holes in the wrong place.

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    Big2dabank (12-17-2015)

  12. #9
    Bald Tire
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    Could be bad IAC or crank sensor, could have something going on with MAF, but they generally throw codes. It hasn't died on you yet, has it? None of these would throw a code unless it died.

  13. #10
    Spilled Milk

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    Hey Big2Bank, did this problem ever show itself? Did you figure anything out with it?
    Quote Originally Posted by rascole View Post
    I'm pretty anal when it comes to poking holes in the wrong place.

  14. #11
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    Quote Originally Posted by BeastOfaTruck View Post
    Could be bad IAC or crank sensor, could have something going on with MAF, but they generally throw codes. It hasn't died on you yet, has it? None of these would throw a code unless it died.
    MAF and throttle body are clean, that was the first thing I did. Truck has never stalled on me, when I was having the problem, I could rev the engine in park and get it close to stall, but it would never actually stall. Now thats its cols here in Florida I can't get the problem to manifest itself, so it has to be heat related somehow.

    Quote Originally Posted by twinmill28 View Post
    Hey Big2Bank, did this problem ever show itself? Did you figure anything out with it?
    Not yet, now that we are getting some cold weather here in Florida it has not been noticeable. I do notice a slight power loss overall and the truck feels sluggish in general, but not the intermittent problem I was having when the truck gets hot. I'm gonna wait until the weather warms up again to start getting a consistent problem when the truck gets hot. Then will finish diagnosing it.
    B I G 2 D A B A N K

    2005 H2 SUT, Desert Sand

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  16. #12
    Bald Tire
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    Might be a leaking fuel pressure regulator. Take the vacuum line off of it and see if there is fuel in the vacuum line...

  17. #13
    All Terrain
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    Could be misfiring but not enough to throw a code. See if your friend can read the misfires live on a scan tool. Figure out what cylinders have the highest misfire and go from there. Swap easy stuff like coil packs, injectors, etc and see if it moves. Could be anything from an almost-bad electronic part to a flat cam.

  18. #14
    Bald Tire
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    Change spark plugs if you havenít and get a catch can. If there is oil in your intake box or tube you need a catch can for the positive crankcase ventilation. Clean the throttle position sensor on the throttle body with MAF sensor cleaner and do a pcm relearn procedure.

  19. #15
    Bald Tire
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    head gasket it oil or coolant is milky.


 

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