Skipping Hummer h2

[La.Swamp Lobster]

Sounds like one of the knock sensors is bad...had to have mine replaced last week...was running rough as a leaf licker on a republicans hairy butt...and had very little power. The H2 has 2 of them, and they are located under the intake..but this should show a code when tested...but then again it could also be a cad. converter that is clogged up!

[PaHumBug]

Mine did this the other day for the first time. Hasn't done it since. I got the feeling it was the tranny trying to shift in and out of OD. I gave it gas to make it down shift and it quit. Hasn't done it since. If yours is doing it at 55mph, maybe thats the same thing. My check engine light came on, but went back off the next time I started it. Since then the check engine light has come on every once in a while, but turns off soon after. Does the light need to be lit in order to get a code?

[PaHumBug]

Originally Posted by PaHumBug

Mine did this the other day for the first time. Hasn't done it since. I got the feeling it was the tranny trying to shift in and out of OD. I gave it gas to make it down shift and it quit. Hasn't done it since. If yours is doing it at 55mph, maybe thats the same thing. My check engine light came on, but went back off the next time I started it. Since then the check engine light has come on every once in a while, but turns off soon after. Does the light need to be lit in order to get a code?

Does the check engine light need to be on in order to get the code out of the computer?

[TXSUT]

Originally Posted by PaHumBug

Does the check engine light need to be on in order to get the code out of the computer?

No.

[trofeo16]

my h2 was doing the same thing. Between 42 and 55 mph the rpm's would be bouncing. Almost like you were slightly revving the motor. No check engine light no codes. Took it to the hummer dealer. They found an entire gm service belletin on the issue. Turns out there is something in the 4l60e tranny that is excentuated by exhaust,intake,maf spacers..etc. I removed all the after market and it went away for the most part. Replaced parts and it came back. If you ask hummer dealer to do a search on bouncing rpms within the service bulletins you will find the article. Hope that helps.

[H2Much]

I had a similar issue as well, ended up being a small air leak in the intake manifold. Once it was fixed, the problem was gone. Only way to check for it was a mechanic who had a smoke machine testing system. Sometimes the check engine light comes on, sometimes it doesn't. The error code just says that the air and fuel mixture is not right, usually hinting to the mass air flow sensor going bad, but this wasn't the case with mine.

[HUMTECH]

If you have an intake(vacuum) leak it will almost always set a lean mixture code and will turn on the ses light. Need a scan tool to force it into closed loop operation and monitor fuel trim levels while spraying air intake cleaner around the intake gaskets with the engine cold, if the fuel trim levels change dramatically the intake is leaking. Dont think this is your issue though. I will put some thought into it and see what i can find.