88 f250 static fuel pressure loss
#1
11-04-2018, 09:59 AM
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88 f250 static fuel pressure loss
To start with it would only crank on dry days. Unless we covered it with a tarp. It wouldn't crank after a rain for a couple days. I changed the distributor cap, rotor. Ignition control module and Coil. Last Friday it was a little hard to start after raining Thursday night and Friday morning but did crank and run twice. I moved it and parked in a different location at a different angle than 10 minutes later it wouldn't crank and hasn't cranked since. I pulled one of the plugs to check for spark and realized the plugs were worn so I replaced the plugs and wires. I do have spark. And I have fuel at the rail at the Schrader valve. I don't have a pressure gauge for the Schrader so all I can do is depressed the needle and see that fuel squirts. I have dual tanks and both tanks have key on engine off prime but they continuously run. I'm not sure if that is normal or not, when I turn the key off I lose pressure at the Schrader valve so I changed the fuel pressure regulator and still no pressure after I turn the key off with both tanks so I'm assuming it's not a check valve issue. I am not entirely sure where to go from here. On a sidenote once it cranks it runs fine except there is a hesitation when you press the throttle fast. But this was before Friday when it stopped cranking at all
#2
11-04-2018, 10:49 AM
Your truck has at least 2 problems maybe more and all are related to it's age and lack of use. Fuel pumps running constantly is a sign the PCM is failing, this is common for trucks this age. Low fuel pressure means at least one of your fuel pumps is dying and your truck has 3.. 1 low pressure pump in each tank and a high pressure pump on the frame. Loss of fuel pressure after shutdown means either the injectors are leaking(does the oil smell of gas) or the selector valve is leaking.
#3
11-04-2018, 11:28 AM
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Thank you very much. I haven't smelled the oil yet. I'll give it a sniff in the morning. I have been thinking the pcm might be part of the problem as that has been a fix for others with damp condition starting issues. As far as the static pressure could I pinch off the rubber line on one or both sides of the fuel rail to narrow down my search or should I try an inline check valve?
#4
11-04-2018, 04:07 PM
It's not just about pressure the motor also needs a certain volume of fuel to run correctly under load. These trucks use a return fuel system that is normally capable of supplying lots more fuel volume than the motor would use under most driving conditions, so that means when you see a low pressure problem it's usually because of a dying pump or in this case it could also be due to a leak in the selector valve that is allowing fuel to go somewhere it shouldn't, so examining that device should be your next step.
#5
11-04-2018, 04:12 PM
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It's not just about pressure the motor also needs a certain volume of fuel to run correctly under load. These trucks use a return fuel system that is normally capable of supplying lots more fuel volume than the motor would use under most driving conditions, so that means when you see a low pressure problem it's usually because of a dying pump or in this case it could also be due to a leak in the selector valve that is allowing fuel to go somewhere it shouldn't, so examining that device should be your next step.
#6
11-04-2018, 06:20 PM
Tuned
If I'm not mistaken the procedure for checking fuel pressure loss for the 88-89 trucks after engine shutdown was:
Install fuel pressure gauge on manifold
Run truck, check fuel pressure, shutdown
Pinch off fuel supply line at engine before fuel rail, if pressure continues to drop, it is leaking at injectors or fuel pressure regulator (at rear of fuel rail)
Pinch off return line, after regulator to isolate, if fuel pressure continues to drop with return line and supply line pinched off, the injectors are leaking
If injectors are determined to not be leaking and the return line after the fuel pressure regulator is pinched off, and the fuel line "pinch-off" is removed at the fuel line inlet, and pressure continues to drop, it is leaking back through the high-pressure rail mounted fuel pump, and that is what is failing.
Is this not the procedure?
I was under the impression that the outlet of the selector valve was not to see rail full pressure.
Install fuel pressure gauge on manifold
Run truck, check fuel pressure, shutdown
Pinch off fuel supply line at engine before fuel rail, if pressure continues to drop, it is leaking at injectors or fuel pressure regulator (at rear of fuel rail)
Pinch off return line, after regulator to isolate, if fuel pressure continues to drop with return line and supply line pinched off, the injectors are leaking
If injectors are determined to not be leaking and the return line after the fuel pressure regulator is pinched off, and the fuel line "pinch-off" is removed at the fuel line inlet, and pressure continues to drop, it is leaking back through the high-pressure rail mounted fuel pump, and that is what is failing.
Is this not the procedure?
I was under the impression that the outlet of the selector valve was not to see rail full pressure.
#7
11-05-2018, 06:58 AM
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Update
update, I decided to bite the bullet and go against my better judgement and sprayed some starter fluid directly into the throttle body. Fired right up and idled fine. Waited about 10 min and she fired up again. Still have the hesitation issue and if I rev it a little then stomp the throttle it will hesitate then backfire through the intake slightly but at least I know the no start is a fuel issue for sure
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