My 92 f-150 4.9l stopped running the other day. It would start then immediately die, start and die. I checked for pressure at the rail, and it read zero. I could hear the pump kicking on for a second when turning the key, but it would not build pressure at all. So I plugged the lines and switched to my rear tank(I had a faulty check vale in the front tank, it would just pump gas out of the rear to the front) and it ran fine for a day. The next morning it wouldn't start, so I dropped the rear tank to replace the pump. Well that tank was about rusted out, so I decided to cap the rear lines and drop the front tank and just fix that one. So front tank dropped, replaced the pump assembly, put it back up, hooked the lines up and still no pressure, I mean none. I've checked the fuses, filter, the relays, the pump kicks on when the key is turned, but won't build any pressure. I have replaced the pressure regulator, and I checked that for gas and it's dry...what else could cause this? Desperate to get this truck going as I need it for a job I'm doing.

 

Sounds like you have a plugged fuel filter now.

 

Checked the filter again, and it's not clogged. The fuel inside came out really clean even after shaking it up. I can also blow through it both ways with hardly any resistance...any other thoughts? Would trapped air in the return or feed sides of the lines cause this? I capped the lines to the rear tank with brass compression fittings and caps back near the rear axle because that's where I could get at them easily, so there's about 4ft of line after the front tank line split off the main line.

 

The return line must go to the tank you are using and not be caped off.

 

It does. There's the feed and return lines coming off the fuel rail heading towards the back of the truck. At the front tank, the lines have a "T" that branches off a feed line and a return line for the front tank and then continue to the rear. I capped just the rear lines off at by the rear axle. I have a complete fuel circuit. Fuel does come out of the Schrader valve, but the pressure gauge I hooked up is reading zero PSI.

 

The gauge will read zero if the fitting is not pushing down on the Schrader valve.
I have seen this before.

 

I think maybe the gauge is not working. I have fuel at the rail, and I just took the plugs out to check them and they were covered in gas. Cleaned them and put them back in. Now I'm waiting for the battery to charge back up from all the cranking I did so I can see if it'll run.

 

check fuel pressure regulator. might be letting fuel bypass back to tank.

 

Does that schrader valve core unscrew like a normal one? Depressurize the rail, pull the core out, try the gauge again.

 

Well, the fuel pressure gauge I was using wasn't working, checked it on another vehicle that runs and got the same zero pressure reading. I did however find out what was causing it not to run...broken ignition rotor...couldn't see the forest for the trees. I guess I was so concentrated on the fuel issues that I wasn't bothering to look anywhere else. Thanks for the replies.