I'm helping my nieghbor with his 2000 F150. It has the 5.4 and an automatic transmission. His wife drove it home from the store and it was running great. The next time they tried to start it, it would just crank over but not start. I don't have a code reader but I checked the basics. The first thing is that the gas gauge doesn't move when the key is turned on. We dumped 3 gallons of gas in and it still didn't move. I checked the fuel pressure at the rail, when the key is turned on, it goes to about 25 PSI and the pump runs for about 1 second. When the truck is cranked, it doesn't build anymore pressure because the pump is not running. I sprayed a little starting fluid through the air intake and it fired immediatly. I checked the cam postion sensor on the bench and it is good. I checked for voltage at the connector and have nothing. The wiring diagram I have from a Haynes manual show the Lt Blue input wire junctioned with the gray/red wire. The grey/red wires have 5 volts on them, but the lt blue wire has 0 volts. I traced the wire back to the connector on the firewall between the PCM and the engine. I had good continuity on it. Does the PCM use other inputs before sending a reference voltage to the cam postion sensor?

Montana Mark

 

It almost sounds like your Passive Anti Theft (PATS) isn't working. That's the computer chip in the key. Without that chip, truck will crank, but it doesn't fire any injectors.

So I'd try a different key first.

 

I tried a different key hoping that was the problem, I had the same results.

 

This is not a cam sensor issue. A faulty cam sensor won't cause this fault. If in doubt, just disconnect it and the computer will "guess" as to injector timing with a 1 of 3 chance of gettng it right on any given start attempt.

25 psi isn't enough. You should have closer to 40 psi at initial prime. Spec is 30-45 KOEO. Try cycling the ignition switch several times to allow multiple priming cycles. If it builds up with repeated cycles, check for restricted fuel lines/filter. The pump will not be turned back on by the PCM until the PCM detects that the engine has started firing (PCM checks for cranshaft acelleration via the CKP sensor).

Basic Steps:

1. Check PATS system for proper operation if present. What is your THEFT indicator doing?

2. Verify Vref (+5v) at TPS connector

3. Check for spark

4. Check for air (crack throttle 1/4 while cranking)

5. Check for correct fuel pressure.

You pretty much pinpointed it as a fuel delivery issue...

Steve

 

Does the cam sensor use a reference voltage? I checked with the ignition on and didn't have squat. The fuel guage doesn't move when the key is turned on. There is no theft sensor on the dash during any starting atempt. Does anyone have a better wiring diagram than what is in the Haynes manuel?

 

Theres a lesson to be learned here, Dont let the wife take the truck to the store.