Chitty chitty bang bang ...please help!

My car is a 96 Pontiac Grand am with 250k miles on it. It runs great except when the outside temp is over 80 and the car has been running for more than an hour.

I can hear a loud Humming noise (No matter how loud I turn the volume up on the radio.) and then the car will quit accelerating. The engine is still running but I can push the gas pedal to the floor and it will not make the car go. If I put the car in neutral and turn it off and turn it back on then it will go again for a bit but it will not work properly until the car is allowed to cool for a while.

I have had the car tuned up and replaced the fuel filter twice. There was something that was cracked in the engine that was replaced too.

This happened a bit last summer but it seems to be starting earlier this year and I think I might need to see if I can get it fixed. Unfortunately every time I have taken it to the mechanic they haven’t found anything wrong because by the time they get to it the car has cooled off and behaving herself. I now drive an hour to and from work and with hot weather coming I may become a menace on the road when I start putting along when we quit accelerating…Help!

Have the fuel pump checked!

Agree; you could also have some form of vapor lock, disrupting the fuel supply to the engine.

The fuel pump is cooled by the fuel it sits in, and by the fuel it pumps. You should keep your gas tank level high to help keep the fuel pump cool.
The fuel may be picking up extra heat on its way to the engine. Heat shields, and heat sources (exhaust pipe, etc.) should be checked, for effectiveness and isolation, along the path the fuel line goes from the gas tank to the engine.
To check fuel pressure, a fuel pressure gauge is connected by a long hose to the engine fuel line. The gauge is taped to the outside rear view mirror (or, placed on the windshield). The car is then driven, and accelerated briskly, and the gauge monitored while doing this. If the fuel pressure isn’t as specified, for those conditions, other tests and decisions need to be made.
The other important test is fuel volume test. Here are the instructions for doing that:
You can download these pages, print them, and give them to your mechanic and tell s/him what you want done. If the mechanic isn’t agreeable, fine another one who is agreeable.

That makes sense since the lower the amount of fuel the worse it gets- but only when it is hot outside…

Is checking the heat shields something I can do? Is there someplace I can find out what it is supossed to look like?

Thank you for your help…it gives me hope!!

Thank you for the help…what causes vapor lock? any ideas on how to figure out if that is what it is?

when I took it in last time they replaced the fuel filter- (they said there was moisture in it) Could the fuel pump be getting water in it from somewhere? Small enough amounts that only when the humidity is high does it disrupt the fuel supply???