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Ron
Ron, ASE Certified Technician
Category: GM
Satisfied Customers: 33423
Experience:  34 year as An ASE certified Tech
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2005 Hummer H2 6.0 at times throws multi misfire

Customer Question

2005 Hummer H2 6.0 at times throws multi misfire codes...just need another techs opinion on this...over the last 6 months its had OEM plugs&wires the updated fuel pump asy from G.M...NO lean codes so I don't believe its a leak or dirty MAF... CUSTOMER
also said it runs like a dog he said its lost power but I drove it and I don't know what he expects for a rolling box...the next thing I was thinking is doing a back pressure test??
Submitted: 1 year ago.
Category: GM
Expert:  Ron replied 1 year ago.

Hello and thank you for you question,

Can you tell me what fault codes you are actually getting?

Customer: replied 1 year ago.
P0300
Customer: replied 1 year ago.
Not all the time
Expert:  Ron replied 1 year ago.

You may very well be right with checking the exhaust back pressure because the H2 has a long history of restricting Catalytic converters so I would sure do that first and see if you feel a power lever return. Try loosing the exhaust up on both banks at the exhaust manifolds till you have a healthy leak and then take it out for a drive. If there restricted which is very likely then you should feel some increase in power.

Expert:  Ron replied 1 year ago.

If after checking the back pressure and you find no difference the the other thing you should try which can cause the P0300 code to set is run the Crankshaft Variation Learn Procedure. See the steps in the link below for this procedure. Copy and paste the link to your browser to open and view them.

https://dl.dropboxusercontent.com/u/104923897/Crankshaft%20Variation%20Learn%20Procedure%20Nov%2019.pdf

Customer: replied 1 year ago.
Thank you, ***** ***** check that out later today
Expert:  Ron replied 1 year ago.

Your very welcome and thank you as well. Please take a moment to rate my service so I can get credit for my time, the question remains open for follow up even after doing so, all you need to do is return to this question if need be.

Thank you again.