1992 F150 4.9 auto dual tanks. I replaced front fuel pump and sending unit, cleaned tank. I hear pump prime and have voltage to pump while running but she stalls after a few minutes of running. I put another pump in and same thing. Funny thing is I can reprime the pump driving down the road and the motor picks back up but shortly after she stalls again.

Runs fine on back tank. The external check valve on the front tank is bad. I get fuel runover out of the front while using rear tank. Is the check valve my problem?

 

I would get the check valve replaced before diagnosis.

 

I cant seen to get the check valve to release from the fuel lines using my fuel disconnect tool. Is there a trick to it? I dont wanna damage my sending unit.

 

You have the scissor style or the little plastic thing? Once I get one side on I usually just grunt the other side in, and push as far as it will go, and rotate a little.

 

Little plastic thing. Check valve is pretty rusty. Soaked her down with some PB blaster. Gonna let it soak tonight. I will let ya know if the valve was the problem. Thanks for the help!

 

No worries! Hope you get it!

 

Well its not the check valve. Got code 542, so maybe a bad ground? Can I run a new ground from the frame straight to the orange wire at the pump?

 

542 (O,M) Fuel pump open, bad ground or always on - - Power / Fuel Pump Circuits

Id say so.

 

Careful there Rex. The ECM actually applies a ground to start the fuel pump motor. The way that circuit is wired, the motors ALWAYS have 12V on them. I would elect for broken wire or corroded connector somewhere, meaning open circuit to the pump. If you're getting run-over in the front tank, that's almost a guarantee the check-valve is stuck, and you're losing fuel pressure when trying to run on the front tank. Test the fuel pumps from the test connector to see if the right one runs based on where you have the switch set. If it runs continuously while the FP test pin is grounded, then you probably don't have a problem. Oh yeah, btw, if you run the pumps from the test plug, you WILL get a fuel pump circuit error code.

 

Well running a new ground didint work either. Im resetting the computer to see if i still get the 542 code. Does the orange ground wire feed both the front and rear tanks? My rear tanks runs fine. Is the computer not recognizing a ground on my front tank?

 

I removed external check valve. Pump voltage checks out good on selected pump using self test. Still losing fuel pressure off front tank. I can reprime pump and she runs fine for a bit but give her gas and nothings there. Runs fine off rear pump.

 

I removed just the return line off my front pump. No fuel or pressure. Is this normal?

 

On my 94, the same problem wound up being the wire connection to the back of the switch on the dash was bad. You could wiggle the wires, and the pump would come on. I replaced the plug, and that fixed my problem

 

Im gonna try that next. I have power to the pump though. Is there something else in the switch that controls something else other than what pump is selected?

 

Mine would power up the pump, then qiut.
I took the switch out of the dash, and went down the road, tweeking on the wires, and it would come back alive. I haven't had anymore trouble with it since the new harness patch