•Iv always used this forum for the longest time. I used to have a 1996 Ford F-150 and iv always got really good responses on this forum and great help. But sadly I wanted something different because I just got bored with the old one. Iv now got a 1988 Ford F-250 (I know this is an f150 forum but same concept) it has a 302 v8. I'll start out with the things iv changed:
-Fuel filter
-Distributor with new cap, rotor, and module on the side
-battery
-starter and solenoid
-Eec relay and pigtail connector
-fuel pump relay
-coil
-all new rubber vacuum system instead of those crappy plastic ones
-new throttle body, iac valve and plenum gaskets
-throttle position sensor
-new plugs and wires
•So iv done a pretty good "get to know the truck" tuneup. Now for the issues
-when I turn the key to the on position my fuel pump in the tank and the high pressure one on the frame both will not turn off. I can do the whole key on key off thing and they'll eventually run for a couple seconds and then cut off how they're supposed to. Iv checked all my wires and grounds literally all of them on the truck. Had to re-splice a few of them. But they're all good.
-when the fuel pumps finally turn off and i can start the truck it idles rough... drops from about 1500 to about 300-400 and sometimes almost dies. Then when warm it falls from 900 to 300-400 and almost dies sometimes.
•some issues I think i need to look into. -the 02 sensor wires have been spliced in a few places but they all seem to be good iv re done a few of the slices
-the tune that runs to the exhaust off the divertor valve is no longer hook up the the exhaust it is just having down due to the previous owner putting on long tube headers and straight piping.

I really hope someone can help I'll respond fast to anything that is posted the only reason I'm posting here is because on all the other forums iv tried no one responds so I figured I'd try on my always trusty old one. Please help iv been at this for 2 weeks now.

 

Probably best place to start would be to measure fuel pressure on both tanks.

 

How do I go about doing that?

 

With a fuel pressure gauge. There's a schrader valve on the fuel rail (LH side of the engine). You should have 30 to 45 psi KOEO, preferably in the 40's.

This sounds like it could possibly be an issue with the PCM (computer). The pumps should only get power for 1 to 2 seconds. Unless the engine is actually running.
Could be a wiring glitch (handyman home repair) but something is wrong in that whole computer to pump circuit.

 

Iv already got a pressure gauge hooked up at the rail. 45 psi koeo. And there's no way I rewired my eec plug wrong it's 5 wires. I do more complicated wiring at work.

 

No knowledge of the V8s, but I wonder how the fuel pumps operate. Do the pumps run for a set amount of time, then shut off, or is there a sensor that 'tells' the computer that the fuel rail has sufficient pressure, then shuts them off?

 

I have no clue. Also i dont know if the fuel pump in the tank is feeding enough fuel to the high speed pump on the frame. I have 3 pumps. 1 in each tank and one on the frame. The left over fuel in the line in front of the high speed may be building up enough pressure to the rail and then no more getting through i dont know.

 

Have you checked fuel pressure regulator ? Is it the same on both tanks ? Check the dual function valve just before high pressure pump It has a filter if I remember right and can cause problems. Just a thought.

 

I'll go home and try the fuel function valve. Iv actually got one. It came with the truck when I bought it from the guy. I'll see if that doesn't help.. no money lost on that one. Surprised I haven't tried it yet

 

Well I got it running a week ago. I put a new fuel pressure regulator on and it ran fine. Now a week later it's back doing the same thing. So I tried the map sensor and snagged a idle air control valve from pull a part and still nothing (I bought the map new). I bet if I put another regulator on it would fix it for another week but I want to fix it permanently, well I say permanently but you know. I don't understand if the truck came stock with the fuel pump on the frame and one in each tank or if the high speed fuel pump on the frame was added. Maybe there's a problem with my return line. I really need some help.