Ive been chasing this problem for the longest now and any thing I can think of doesnt fix it. I have a 92 f150 4.9l, while im driving around town and I come to a stop light my truck will all of a sudden die and I can start it right back up again. I have pulled codes and got 111,628,634. I have checked fuel pressure and I got 45psi but the needle bounces around from 45-49psi. While I checked the fuel pressure it never cut off it did sputter a little and I noticed the fuel pressure drop but picked right back up. I thought maybe it was a fuel pump but it has this stalling problem on both tanks. The front pump is new and the back needs to be changed, it still works its the original one though. I have also made sure my filter isnt clogged. Could a fuel selector valve cause a problem like this? Im at my wits end here and cant figure this out.

 

Your 300 needs right around 60psi of fuel pressure to run right. Cycle the key a few times and see if it builds to 60, if not replace the high pressure pump if you have one on the rail. (I cant remember when they changed fuel systems) If you have only an in-tank pump replace that one.


Edit: Just saw you've replaced a pump, pull the vacuum line off of the fuel pressure regulator and see if that helps or its wet, you may just want to go a head and replace it as that looks like the next reason for pressure drop.

 

I just have the two in the tank. The front pump is new. The rear I plan on changing soon anyway.

 

Did you replace/check the regulator?

 

I didn't replace it but I did check it. When I take the vacuum hose off the fuel pressure raise to about 50psi.

 

I'd get a new regulator. We've now seen that your pump still wants to build pressure but your regulator is probably week after all these years. I recently read that if you want to make triple sure your pump is good pinch the return line shut and see if pressure builds to about 80-85 psi, but this isn't necessary because you know you have a new pump.