Bought an 08 Hummer H3 3.7L a couple months ago. Was running and driving perfectly and suddenly lost power on the highway a couple weeks ago. It has brand new spark plugs, catalytic converter, ECM, and throttle body. Have installed MAP, MAF, Crank, Cam, coolant temp sensors. Still have no power. Speeds tap out about 40 mph, can’t pull hills, and fully pushing pedal makes the engine rev to above 3000 rpm while not pulling. Engine sounds bogged down and has to turn high rpm to gain any speed. There are no DTCs on 3 readers and no lights. Anyone have any ideas as to what could be killing the power? I appreciate any suggestions!

 

clogged cats?

 

I just installed a new cat

 

That leaves another one to be clogged because I5 H3s have a Cat in the Exhaust Manifold and a Secondary Cat after that. Not likely....

Anyways, did this start before, during or after you have been throwing parts at it? How many MILES on the truck?

When was the last time you changed the Trans Fluid and Filter? Fluid level and quality? If the engine appears to run smooth and normally, but the truck is not responding to throttle demand (ie speeding up), that is your Auto Trans on the way out. Do you understand what happens when an AT needs a rebuild?

 

Head over to Utube land and watch PineHollow Auto Diagnostics (Ivan is a literal genius lol) Or Mr. O at South Main Auto. Digest hours of videos and you just might figure out your problem. You for sure will be entertained and educated. They do not work on our specific brand but they do cover a lot of territory.
ScannerDanner is pretty good too.

 

Hi. Wondering if you had an update and if you found out what the problem was. We have 06 hummer with same problems.

 

Same problems as what?

Welcome to HF.

When you ask a tech question, you do not need to tack it on the end of somebody else's question. You should always include Miles and a list of recent work done just prior to the onset of your issue(s).

Circling back to the question for the OP that disappeared ......

When was the last time you changed the Trans Fluid and Filter? What is the Fluid level and quality? If the engine appears to run smooth and normally, but the truck is not responding to throttle demand (ie speeding up), that is your Auto Trans on the way out. Do you understand what happens when an AT needs a rebuild?