Hey all, i am completely stumped on a 2000 ford with a 5.4 ltr auto 4wd truck. Initially the ECU was bad so i replaced the ECU. Once i replaced the ECU the truck fired right up. I checked the fuel pressure once the vehicle got running an it was low ( after about 45 min of running at idle the fuel pressure would drop to 26 psi). I replace the fuel pump and filter and the truck has an insanely hard start and sometimes no start. Today the truck fired right up and ran great. When i tap the throttle the idle hangs at about 1800rpms for roughly 45 seconds and this happens repeatedly. When I shut the truck off and go to restart it it will either not start at all, attempt to start but not start, or it will take a long time to start. At this point I really need some help getting this thing figured out. If you can help in any way please let me know thanks.

 

Have you confirmed good fuel pressure all the time with the new pump and filter? I don't know if your truck has a throttle position sensor? Just guessing here. I'm no expert.

 

The constant fuel pressure is great at idle and key on and off. This morning i came in and went to start the truck and it started right up and ran but the idle was high at 1200rpms. I let the truck run for about 30 minutes then turned the truck off and waited roughly 2 minutes and went to restart the truck. I cranked the truck over for roughly 45 seconds continuously. The truck would attempt to start but wouldnt. Then at about the 45 second mark the truck fired up with a high idle. I am at a loss with this truck. I have been a ford truck for over 15 years and have not ran into this problem before.

 

Vacuum leak? That could explain your symptoms

Even the fuel pressure regulator is vacuum controlled

 

have checked for both a vacuum leak as well as tried different test with vacuum off and on the fuel pressure regulator