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Dan, Technician
Category: Chevy
Satisfied Customers: 23979
Experience:  Independent Shop Experience, 2 Year Automotive Diploma, & Access to Information Database
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2007 Hummer H3. I have a misfire under a load between 30-40

Customer Question

2007 Hummer H3. I have a misfire under a load between 30-40 mph. The engine runs smooth at idle and runs fine all other times. I changed the coil pack and spark plugs using ac delco parts. It still has a miss under a load and the code p0303 came back?
Submitted: 1 year ago.
Category: Chevy
Expert:  Dan replied 1 year ago.
Hello, my name is***** you have P0303 that would either mean injector or internal engine problem such as cam lobe wear. Swap injector with another cylinder to see if misfire follows injector, if so replace. If not, then next step is compression test and cylinder leak down test to see what is going on with internals. Let me know if you have more questions or if there is anything else I can do to help. Thanks.