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Go Back   Hummer Forums by Elcova > Hummer H3 Discussion Forums > Technical Discussion and Customizing your H3

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  #1  
Old 08-24-2008, 07:43 AM
hawaiih3 hawaiih3 is offline
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Default P0300//mulitiple misfire

1st time check engine came on was while I was in line at a drive thru so I ran a scan with a Gynesis and pulled P0303 and P0300 so I replaced all plugs
with iridium (denso)-cleared codes and ran another scan. No codes. However, the scanner can run live data stream and as I am running live data I can see mulitiple misfires and it records the count in history on each plug . But the misfires only occur during idle and not under load like cruising speed on the highway. for instance if i rev the engine like just tapping the throttle I can feel a hesitation of power and the live data reads mulitple misfire but then clears it self but no code or engine light comes it just continues to count and clear its self. I checked for a vacume leak found none, checked to see is the valve cover to intake box hose was cracked or loose and it wasn't. I replaced the # 3 coil, but still no change. There is no crankshaft sensor code nor camshaft sensor code, starts fine and runs fine but when I run live data I can see the misfires occuring. Anybody have any ideas on what is going on or lead me to possible cause?

JJ
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  #2  
Old 08-24-2008, 03:10 PM
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Default Re: P0300//mulitiple misfire

Dirty fuel, fuel filter, vacumn leak, gap, timing...

let us know...
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  #3  
Old 08-24-2008, 07:17 PM
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Default Re: P0300//mulitiple misfire

What year is that beast and what engine do you have?
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Old 08-24-2008, 08:14 PM
hawaiih3 hawaiih3 is offline
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Default Re: P0300//mulitiple misfire

Thank you for your input:


I have the 2006 H3 3.5L/L5 engine. Prior to code pop up I used Chevron fuel but always fill up with Philips 76, I did check for vacume leaks didnt find one ( I checked the air intake tube, the air box and the valve cove to air box hose), I just put in new iridium plugs and I did check the gap they were .043 (pre-gapped) which is where they should be but I went ahead and regapped them to .041 just to make sure but no change at all,I havent tried the fuel filter. The rpms on the live data stream show from 611 to 634 at idle it is not a smooth a steady graph reading and did find that to be odd. I have appr. 46k miles with no major mods except the K&N filter which I had in there about 1 1/2 years with no issues, and only use regular unleaded ,every once in awhile i do give her supreme but never had light pop up.
TY
JJ

Last edited by hawaiih3 : 08-24-2008 at 08:52 PM.
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  #5  
Old 08-24-2008, 09:28 PM
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Default Re: P0300//mulitiple misfire

time to buy a new one...!
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  #6  
Old 08-24-2008, 11:47 PM
Ryan Graham Ryan Graham is offline
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Default Re: P0300//mulitiple misfire

Head/valve problem? You'll have to do a compression and leak down test to verify. I had a P0300 and the dealership did an injector cleaning. The code hasn't come back, but the intermittently rough idle is still there.
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Old 08-25-2008, 12:13 AM
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Default Re: P0300//mulitiple misfire

I bet then did not clean the fuel/injector system completely...

If you have any crap in your tank and it gets into the injectors .......

You need an ASS HOLE to ELBOW !!!
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Old 08-25-2008, 05:08 AM
hawaiih3 hawaiih3 is offline
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Default Re: P0300//mulitiple misfire

Thank you Ryan for your advise. As a matter of fact just this morning I introduced a fuel injector cleaner in the system it runs a bit more firm and I can feel a stiffer pedal I may have to introduce another bottle and see how that goes. I just ran a live data stream test but I think I might have one very dirty injector # 3-- keeps coming up on the live data stream, however, there is no check engine light coming on. Either I do a -on engine-fuel injector cleaning with the system or remove them and have them cleaned.
TY

JJ
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  #9  
Old 08-26-2008, 01:27 AM
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Default Re: P0300//mulitiple misfire

Have the dealer run your vin and see if yours was in the batch that had poorly hardened valve seats or guides or both or whatever they did wrong. That might be it. Those are all the symptoms and they will not go away if that is it. It usually shows up before that many miles "if" that is the problem.
If so,
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Last edited by Hunner : 08-26-2008 at 05:00 PM.
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  #10  
Old 08-26-2008, 02:02 AM
Ryan Graham Ryan Graham is offline
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Default Re: P0300//mulitiple misfire

If you narrow it down to a fouled injector (either by swapping with an injector from a cylinder with no misfires or injector balance test) then I would probably just replace it. I say this not knowing how much an injector for the H3 is, but I haven't had very good luck cleaning injectors. Please keep us informed as to what you find
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  #11  
Old 08-26-2008, 04:11 PM
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Default Re: P0300//mulitiple misfire

I'd say it is the cylinder head!

Take it to the dealer and get it fixed if that is the problem.
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  #12  
Old 08-26-2008, 04:58 PM
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Default Re: P0300//mulitiple misfire

Like Ryan said, get them to do a leak down check. That was how they confirmed my problem. They have done several at the small dealership I go to.
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  #13  
Old 08-26-2008, 11:31 PM
hawaiih3 hawaiih3 is offline
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Default Re: P0300//mulitiple misfire

Update::

I have introduced the fuel injection cleaning solution in the system, actually several bottles (gradually) and I can feel a better/stiffer pedal. I run the live datastream while I am driving and all cylinders show "0" misfires count. While I let the engine idle I show no misfire count on any of the cylinders but # 3 (before that it was all of them)but I must say that they are very few now, not as before. I believe I just had very dirty fuel injectors(especially #3). Overall engine performance has been great even before I noticed anything, usually with a misfire error the engine idles very rough but not in this case. If I have never ran a live datastream test I would never know there was an issue, usually most folks run a scan to check why the check engine light has come on. I will be keeping an eye on this and see what happens. I am very hesitant to take it to the dealer because I have bad service in the past ( another issue for another day)and I don't trust them and the bad thing is that here only dealer here in Hawaii.

Thanks to everyone with your input.

JJ
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  #14  
Old 08-27-2008, 01:09 PM
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Default Re: P0300//mulitiple misfire

Quote:
Originally Posted by RubHer Yellow Ducky
I bet then did not clean the fuel/injector system completely...

If you have any crap in your tank and it gets into the injectors .......

You need an ASS HOLE to ELBOW !!!

BTW....as I reread my comment I ment to say "AN ASS HOLE TO ELBOW SYSTEM Cleaning"

Hope you didn't take offence at my lack of completion....
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  #15  
Old 08-29-2008, 02:36 AM
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Default Re: P0300//mulitiple misfire

I actually didn't understand it but knew from your other posts that you didn't mean any harm so I just skipped over it
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Old 09-15-2008, 02:12 AM
hawaiih3 hawaiih3 is offline
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Smile Re: P0300//mulitiple misfire

Hello,
Just here for an update on the mulitiple misfire (P0300) that I was dealing with; after about 3 weeks the of running the vehicle with STP (black bottle)(ran a bottle every other fuel tank fill-up) the check engine light has not returned. So, the issue was clocked fuel injectors, I am sure a good high pressure injector cleaning might be helpful as well but the STP bottles helped alot. Initially I ran 2 bottles of that stuff with a half tank helps in getting a less diluted product thru the injectors, no harm will come to your engine, the company also reccomends or at least suggest that it is okay to combine other STP products if so desired. Thanks to all that assisted or advices on my issue.
Have a nice day!
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  #17  
Old 09-15-2008, 02:18 AM
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Default Re: P0300//mulitiple misfire

SEE !!!

I knew you needed that A** H*** to Elbow !!!
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