help me Hummer experts
2004 H2 , 100K miles, K&N cold air intake
last summer my engine temp gauge went crazy showing it was boiling hot way past the max.....I also had poor acceleration and needed to back off the throttle to speed up.....it was 100 degrees in florida …..I disconnected the battery and it reset the gauge and the Hummer drove great......then it did it again a month later, shows a 3xx code and knock sensor issue and temp gauge buried past red......I cleared the codes, reset by disconnecting the battery......sometimes it resets perfectly and sometimes it takes 3 or 4 resets to drive correctly......same thing everytime…...super sluggish throttle, cant give it too much gas or it wont go, barely touch the pedal and it accelerates, engine light comes on and code shows knock sensor, wont shift properly, or downshift...…….disconnect battery and it runs perfectly


its almost like a need a battery disconnect in the cab to quick fix the problem...….it did this while in locked low crawling in a claypit recently and I again had to get out and disconnect the batteryreset ecm to get out of the woods

any ideas ??? it runs perfectly for a little while and then resets itself to crap mode for no reason

 

Have you replaced the knock sensors?

 

 

First thing I might try would be to verify that all the grounds and good and solid. Could probably find a lot more tips on one of the GM truck forums since the trucks are far more common and use essentially the same engine and electrical system. Just an odd one and troubleshooting something that is so random is not always easy.

I'm not sure what the ECU does if it does detect severe predetonation (knock) but it very well might be the knock sensors and its going into a sort of limp or safety mode by drastically cutting the timing or something to prevent engine damage.

If you have ever cleaned well under the hood (quite likely since you go wheeling) then its possible water got in and the knock sensors are corroded and rusty. Common problem on GM trucks - they are directly under the intake manifold. There is a foam block to prevent stuff from getting in there but it does. If you are not aware, NEVER direct water to the top front of the engine under the air intake tube. It can and will get past the foam block and run under the intake. I've replaced mine, not terribly hard but not at all fun to do.