86 F150 EFI 302

The problem I am having is when the engine gets warm after about 20 minutes of driving. Runs fine when cold.

Two weeks ago the fast idle quit working after I started the cold engine but the engine has otherwise always ran fine, but I did have to adjust the idle speed up after that happened because it would not idle. Yesterday after driving about 20 minutes the engine started hestating and cutting out. It does not hardly have enough power to pull itself. Let it cool down and it will run fine for about another 20 minutes. Last summer when it would get above 90 degrees it would do the same thing and sometimes quit all together untill it cooled down. I thought it was vapor lock but now I don't think so.

I have changed fuel filter in the frame rail. I have noticed when it starts running rough there is a relay in back of the black vacuum booster that sits behind the battery thats clicks like crazy.

It acts like the fuel injectors are not getting regulated. There is pressure in the fuel rail but I have not checked what the pressure is. There is a vacuum pot on the fuel rail and I can disconnect the hose and it does not make any difference in the engine even when it is running good.

Any ideas on what I need to look for? Is it the fuel pump?

Any help is appreciated! TIA!

 

I might add that the problem started after the weather warmed up to 20-40 degrees from the -10 to 10 we had been having. The truck has 210000 miles but the motor has only 50000.

Any ideas please!

 

Just drove 2.5 miles. Started and was running fine when I shut the engine off. Restarted in about 15 minutes and it was running like it was only hitting on one cylinder. Definately a fuel lean problem.

I have check for vacuum leaks, replaced the ignition module on the distributor. It seems like engine heat is causing a sensor not to work when it gets warm. Would the temperature sensor going bad do this? Would a bad throttle postion sensor do this? I have unplugged the throttle position sensor when the engine has been running good and also when it has been running bad and have not seen any difference in the way the engine runs. Is it possible the computer is bad?

 

I found the problem. The ground wire on the negative battery cable was corroded and not making a good connection. Runs like new now.

Thanks everybody for all the great input!!

 

It was nothing!