ok so i have thrown a bunch of money at this problem and still cant figure it out.. both my father and I are mechanics (he has been a truck mechanic for 30+ years).. here is what we have so far.. a 1985 ford f150 with a 5.0l v8 fuel injected (dual tanks), it is a 4spd 4x4.. The problem is as follows. the truck will start and run fine but after about 20 minutes of continuous driving (takes less the hotter it is outside).. it will stumble and act as if it is running out of fuel (inside the truck it feels as if someone is popping the clutch over and over again).. i hooked up a fuel pressure regulator to look at the fuel pressure when this is going on and the needle will show anywhere from 35-40 psi when it is running fine and <20-25 when it is stumbling and jerking the car around (running out of fuel).. now when this happens i usually pull over, as i do not want to cause a accident, and if i try to restart it it will idle very rough (barely idle) or wont run at all.. so far i have changed both in tank pumps, cleaned tanks, blew out the lines with air, changed boost pump on the fuel rail, changed both fuel filters, changed the fuel presure regulator, the line from the boost pump to the fuel rail, changed the ignition control module, spark plugs, spark plug wires, cap, alternator (for other reasons), exhaust (its same as stock, but all new).. i honestly dont know what else it can be.. it is obviously running out of fuel.. of course there is gas in the tank etc..any help would be appreciated


UPDATE as of 2 seconds ago.. i disconnected the battery and came back 30 minutes later and reconnected it after cleaning terminals.. now the truck wont even start.. im thinking this means the PCM is shot but im not sure.. also, does anyone know where the pcm on this truck is located???
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found the pcm, dont know how to get it out.. have to take off the dash?
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you might check out your vacuum control valve system and see what happens after they warm up to opening temperature. maybe theres a bad vacuum line or something. i would check out the PCV valve too. could be something other than a fuel system thing. maybe your fuel tank vent tubes are plugged?

 

doesnt explain fuel pump whining and fuel pressure dropping to zero (previously).. now fuel pump wont kick on at all
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hey
maybe this will help it tell step by step what the fi /computer is doing..

http://fordfuelinjection.com/?p=64

scroll to the bottom

good luck \
i hate efi

 

well you never said anything about fuel pressure dropping to zero and the pump whining

 

I had strange things happen on my 85.. It was the gizmo underneath in the distributor..If you have 20-25 psi the motor will still run fairly well...esp at idle.
Did you say if you had spark?...On mine cyl 1 and 8 are not running I need an elec drawing of the injector circut...


Dick

 

it has spark and it is in time, the "gizmp" you speak of is the ICM (ignition control module), which i have already changed..

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It almost sounds like the fuel pump might be overheating and failing after a little while. Or the circuit going to it may have a partially broken wire that as it gets warmer the resistance goes up and it finally stops working until it cools down. Also you may have a fuel pump relay that is going bad.

 

well what ever it is has gone completely bad because the boost pump will not turn on at all, meaning no fuel pressure which means truck will not run.. which in my mind is a good thing.. easier to fix the problem.. dont have to try something drive it for 20 minutes get stranded and then have to drive back
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