This issue has been stumping the mechanics. My wife’s HHR has 113,000 miles on it and has been trouble free up to now. The last two months it will suddenly not want to start after being driven for 20 - 30 minutes and then sitting for an hour to 75 minutes. It turns over but won’t start. Even more strange if you then wait for a full hour it will start right up. Mechanics are stumped as they cannot duplicate the problem.
What kind of mechanics are these? If the engine turns over then it’s an easy process to eliminate the ignition system or the fuel system. The most probable cause in my mind is the ignition coil or the ignition module. Heat will cause one or the other to fail and when they cool off they will function again. I would start there. See if there is a strong spark visible the next time this happens. It should be bright and blue. A yellow spark will not be strong enough to start the engine.
My wife’s 91 Ford Taurus would run for 45-60 minutes then stall. After an hour or so it started right up, it was the fuel pump. The mechanic had to hook it up to the diagnostics machine and just let it run till it stalled to get the diagnosis.
Chances are the trouble is due to a intermittent problem with the ignition system. If that turns out to be the case then the first thing to check is make sure power is getting to the ignition system. In order to determine if this intermittent trouble is due to an ignition problem or possibly a fuel delivery problem, leave a can of starter fluid in the car and when the trouble happens again simply spray a small amout of starter fluid into the air intake of the engine and try to start it while the trouble is occurring. If the engine still doesn’t fire up then you know the ignition system needs to be checked. If the engine does fire up briefly then you have proved the fuel system needs to be checked out.