Regarding 1990 f150 4x4 5.8 liter.

Installed new long block, engine starts up fine and runs well when cold for about 1-2 minutes (engine revs well and is very smooth and responsive).

Then the RPM drops to almost idle RPM even with gas pedal to the floor. Seems as though the electronics isn't staying in touch with the gas pedal position after the engine starts warming.

Anyone have thought on the possible problem?

 

Does the engine start up again normally? Wondering if fuel pump is not comming back on when engine is running. Remember the pump runs for a short period of time during start mode. After engine has oil pressure, the computor then engages the fuel pump relay and turns on the pump again. No pump, no gas, and the engine stops.

 

When it will get worm, read the codes with engine running. A how-to is on a sticker in the manteinance section. Then post the results.