Fuel delivery erratic after 3-4 hours on highway

I drve a 1987 Buick Skyhawk, 145,00 miles, normally runs well except on long drives over 3 or four hours. Then it seems to get gas off and on, particularly dying out as the gas pedal is let up. If I let the car sit for half an hour, I can drive 50 miles or so. If I let it sit overnight, It will be good for another 3-4 hours. What is it???

Well a logical guess would be a fuel delivery problem. That could be a fuel pump that is getting weak, plugged fuel filter, or even the sock filter in the tank. I guess if the fuel filter has not been changed lately, I would do that first. Then you really need to get a fuel pressure tester on it when it is having problems to see what kind of fuel pressure you have. It could also be vapor lock from the fuel lines heating up but that is a symptom of a bad fuel pump too.

I agree 100%.

Wile I also agree with Bing, I would not rule out the possibility of an ignition problem. Some get heat sensitive. Plugs wires and most likely coils.

Good Luck

Thanks for the help. I’ll check out the fuel pump. Still don’t understand how it can pump well enough up to the four hour limit.

Try opening the gas cap and see if there is a huge suction sound when the problem occurs. If the tank isn’t venting properly, it may take quite a while for the pump to evacuate the tank before it becomes too hard and it starts failing to supply fuel. Just one thing to check.

This would seem to be a heat failure problem not a fuel pump issue. I would be suspect of a ignition control module. The fact that the problem starts after the engine is hot then it runs fine after it cools seems to point to a ignition module more than a fuel pump. This car was well known for module failures due to where it was located.

I agree with at least testing the fuel pressure to at least eliminate that as the cause but look closely at the module.