I have a 1991 F-150 with the straight 6. Roughly 140k miles. Truck sat for several years and I finally wanted to get it going again, and found that the fuel pump had failed. No biggie, I dropped the tank, cleaned the tank, put in a new fuel pump and a new fuel filter. Put 5 gallons of fresh gas in the tank and after a few minutes she fired up. I let it run for about 10 minutes, then shut it off, ran to the store, got another 5 gallons of gas and injector cleaner. Put the gas and injector cleaner in and now when I turn the key to the on position, the fuel pump kicks on and wont turn off, and the truck won't start. It's like it's not building up pressure in the fuel system now. But 15 minutes earlier I started it and shut it off several times. Then it sat for 15 minutes while I got more gas and now this. I turned the key on, and popped the shrader valve on the fuel rail and there was plenty of fuel there. Is it possible the fuel regulator is stuck open and it's just cycling back to the tank? I'm really confused because it did start...any ideas would greatly be appreciated!

 

When you first turn the key on, the ECA (computer) provides the ground for the fuel pump relay to run for 1-2 seconds. Unless it sees an RPM signal the fuel pump should stop. It could be the fuel pump relay is sticking or the computer is still providing the ground , which it should not. Try removing the fuel pump relay and see if the fuel pump stops, then try reinstalling the relay . If it doesn't run anymore, the relay is probably sticking closed. If it continues to run , need to confirm the fuel pump relay is still getting the ground whether from the computer or some other way. Check the diagnostic plug for corrosion because there is a terminal in that plug that when grounded with the key on will cause the fuel pump to run.

 

Thank you for responding! So my only thought, is wouldn't the truck still start of the relay was stuck closed? It turns over great but won't attempt to start at all, and I'm not smelling fuel, so I'm not flooding the engine...it's like the pump is pumping it through the system and returning it right back to the tank...

 

To address your concerns, why not try some carb/choke clnr and see if it starts ?
Did you check if there is spark available?
Best way to confirm if fuel pressure is correct is to use a fuel pressure gauge at the schrader valve. Press should be 35-45 lbs.

 

Not to argue with Mr. Hanky, but the correct fuel pressure for the straight 6 was 55-60 PSI. This was one of the few that used pressure this high; the Tempo was another when it went to EFI in '92 (I hope those are ALL in the junkyards by now!).
You might want to thump the EEC power (brown) and Fuel pump (green) relays that were installed in a box directly behind the air filter, however, sloppy techs would rip them out and let them hang, in which case water and condensation would make them stick and create all these problems.
Also, if the fuel pressure is holding, then if you have access to a code reader, look for a code 14 or 18; this is the TFI crapping out, and would mimic no fuel pressure in the first gen EFI like you have.
This was an outstanding engine that was made forever. I had 3 fleets with many of these in trucks and vans, and they were fun to work on.

 

It's a good thing somebody is awake ! If the description was any bigger it would have come out and bit me ! Thanks Greasemark, for stating the correct fuel pressure for a 6.
Have to agree they were a durable engine had many in the fleets I had to service.
I never did find out how one of the guys managed to drive a rod right out the side of the block ! The only horror I can remember was the cost to replace the converter because they were so expensive when the thing rusted out.
I did try to stay with OEM .

 

Thank you for all the input. It ended up being bad caps on the ecm. Pulled the ECM and found two popped capacitors and the third was only attached with one leg. Pulled them off and put new ones in and now she runs.

 

What would you attribute to the popped caps?

 

possibly jumped backwards?

 

Nope, just old and sat for a while. I guess it's a common occurrence on these motors. Someone on another forum tipped me off into looking at it.