I have an 2003 H2 with 145000 mls. It was running perfectly. It had an exhaust leak when we purchased it. When we got that fixed is when the trouble seemed to start. When you accelerate on an incline it doesn't want to go and the engine light comes on and blinks until you get over the hill and let off the gas. Then it progressed to doing it even on flat ground. Two shops have checked the compression and said several were low (but the two reading did not match at the two shops). Both wanted to sell be a new motor. One did say the catalytic converter was bad & may have backed up into the motor to cause the motor damage. Someone told my husband that the catalytic converters could be sending the truck into limp mode and making it run like that. He had the truck straight piped. At first it seemed better then started doing the same thing again. It may be the motor, but my gut just can't let go of the fact that it will run perfect at times (sometimes when its cold & sometimes when it is warmed up). Also, is it possible for the motor to be shot and it not use oil, not smoke, and not run hot??? The only codes that came up was an old mis fire detected code and an HVAC actuator circuit code. The closest Hummer dealer is 2 hours away so we started with local people we've used before. Not opposed to going to a dealer if there is a chance its not the motor. If it is the babies going on a one way trip & mommas getting a new one!

 

Personally I'd start with replacing plugs and wires when I get a misfire. To diagnose a backed up catalytic converter you just need to take the temperature of the exhaust both before and after the cat to determine if its working or not.

 

I'll say that is a catalytic converter issue. I had that problem happen to me before on one of my SUV.. Clogged up catalytic causes misfire code and burns up the HVAC actuator due to high heat..

 

mine was replaced for free under a bulletin that the dealer found. I would ask them to run your vin. I don't remember the bulletin information though.

 

Thank you everyone. We changed the plugs and plug wires first, but long before they told us the converters were bad. So we will do that again. Then we will go to the Hvac actuator issue. This whole ordeal I keep telling them that code comes up, but none of them have ever looked at that or fixed it. Just couldn't jump right into "the motors bad" when nobody had looked into what the truck is telling them is wrong. I will let everyone know how it goes.