Two weeks ago I had been running my fuel tank into the red to guage MPG. When arriving to my kids baby sitter (which is on a 20% grade) the vehicle wouldnt start. I thought it was due to a inability for pump to pull fuel from the tank. I push the SUV into the garage which was level. folks on the HummerX forum told me this is not possible and that it might be electrical and or fuel vent tube. The H3 started after about 5-6 min of resting and attempts to start.

OK so UPDATE!!!!!!! It happen again today, and yes at the very same place, same time of day, but I now pull into the garage every time so as not to be on an incline. I had a half tank of gas today and when the wife and I got back into the suv it wouldnt start!!!!! (cranks over with lots of power) Its weird that both times, the vehicle will start for about 2 sec then when I shift into reverse it dies out and wont start again for 5-7 min.

My new theory is that we climb several very long and steep hills to get to the babysitters. Probably about 6 miles of 10-20% grade road until we hit our destination then I shut the motor off. I noticed that when I turned on key temperature gauge was above the half line at about 3/4 (I miss the days of actual temperature numbers on the dial!). I have plans to do a radiator flush as my last inspection revealed that the fluid was brown, meaning this thing hasn't had any service except for oil changes in the past 54k miles.

So again today after about 5-6 min of rest/starting, the vehicle starts!! :/ Worst part is I call Onstar to ask for a diagnostic and they tell me they can only help me if the vehicle is running?????? :wall: I did call them after and ran diagnostics, no codes, no issues!

So my new theorys are:
1) The Hummer actually wants to STAY at the babysitters, not hates it!!!!!
2) Shutting off engine after climbing steep hill is causing temperature to rise so high that some kind of sensor will not let it start until cooled down.
3)Maybe the vent tube on the fuel tank has spiders and going up in elevation is causing a vacuum in the fuel tank???

THanks again folks for the discussion!
Zach

 

Loosen your gas cap before you go to the sitter next time and test your vacuum theory.

3/4 temp guaue is not overheating.

 

Thank you Doc for the tip on the gas cap, genius!!! Gotta admit that im worried about even shutting the vehicle off tomorrow am. Any ideas on what else could cause this? We drive the vehicle daily 40+ miles mixed with about 5-6 starts and no problems, except for these two incidents that were very early in the am. WEIRD!!!