My H2 was doing that... I replaced my mass air flow sensor & it felt like a different truck! After reading this thread I'm gonna change my gas filter before it becomes an issue.

 

What year is your H2? Not all of them had serviceable fuel filters...

 

mine was also doing that, i pulled the throttle body and airaird throttle body spacer off, clened both of them for over an hour with carb cleaned till spotless. ran a bottle of seafoam in the tank. the check engine light went out and the truck runs a much better than i bought it brand new. amazing. i also adjusted the cold air intake and tightened the clamps, now the trucks throttle responce is amazing.

 

Loses power when I accelerate my 2003 Hummer H2

I know the capability of its power when I exhilarate, This is my second H2. Car makes a lot of noise but the speed doesn’t pick up as it should.

I changed the wires and spark plugs, it’s a little better but still no where near the other power it should be. Your input would be greatly appreciated.

Thanks in advance

JB

 

Have you got an aftermarket CAI on it also ? Any codes thrown ?

 

I have a aftermarket CAI but I had the same no power issues prior to installing the aftermarket CAI, also the engine light isn't on at all

 

2003 Hummer H2

 

How can I tell if the ignition coils are bad?

 

Pull one of the spark plug wires off while its running and feel the end of the wire....

Just kidding. Do NOT try that, will not kill you but its a pretty good shock.

You can unplug the coils (not the spark plug wire) while its running and you should notice a significant change in the idling (since one cylinder will not longer be igniting its fuel). If one has no change at all than I'd look further into that one. I have don't this but its not a conclusive test and will also likely turn your check engine light on. I say not conclusive because a bad spark plug or plug wire could have the same affect.

Also as yours is a 2003 yours DOES have an inline replaceable fuel filter. Kind of a pain to change. Do some searching here on the forums and on Google to find the exact location and tips on releasing the fuel line connectors from it. Could be a thousand things though from a clogged fuel filter, plugged up cats, fouled or incorrect spark plugs (only use AC Delco plugs), bad or failing plug wires, dirty throttle body, clogged air filter, bad O2 sensors, etc, etc.

 

You replied in the wrong thread but I saw it...

4 mpg, yeah there is a severe problem. Something is very very wrong. I drive pretty hard and around town mine is staying right at 10.3 mpg.

Shortly after I got mine I did do a lot of small updates. Replaced both knock sensors (another part to ONLY use ACDelco brand on), valley pan gasket, intake gaskets, valve cover gaskets, spark plugs (only use ACDelco #41-110), Taylor spark plug wires, new belts. While I had the intake off I soaked it and cleaned all the built
up oily goop out of it, cleaned the throttle body, cleaned the MAF, fuel filter.

Since then I've replaced the entire exhaust system with new high flow cats, both upstream O2 sensors, new brakes and rotors. Still a lot to do as well but its 14 year old vehicle with 115,000 miles on it so I figure most of this needs to be done. When I got it the fuel economy around town was right around 9mpg. So all I've done has helped.

Other things to check for, get a mechanics stethescope and listen for any air leaks around the intake and rubber hoses. If you have an leak in one of the vacuum lines that can cause problems. Air intake - make sure its fully on the front of the throttle body. You really need to check the ECU for any stored engine codes, etc.