Help! 90 F150 no start!
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Joined: Jun 2006
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Help! 90 F150 no start!
Hello all, I am new to this group and hope I can draw on the groups knowledge. I have a 90 F150 4.9L 4X4 manual supercab with dual tanks. I have replaced the fuel filter, fuel pump relay, fuel pressure regulator and 18 months ago both tanks and fuel pumps. When the truck is turned on the pump is supposed to cycle while pressureizing the system and then the truck can be started. This cycle should be seconds. Over the last year the cycle time has grown longer and longer to the point where the pump runs until the battery is dead without pressurizing the system. The truck will not start and it does this regardless of which tank is selected. The pump just runs and it is not pumping into the other tank. I am at my wits end, I have been told to look at the ECU but I am tired of throwing parts at this thing with no results. Any help is greatly appreciated!
Thanks
Patrick
Thanks
Patrick
Fleet Owner
Joined: Aug 2005
Posts: 23,667
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From: Easton,Ks
How do you know the Fuel pump is not pumping?
The pumps do not run until they pressurize the system.
Have you put a gauge on it?
The pump will only run for two seconds and then the EEC will turn it off.
The EEC has no idea of what the fuel pressure is.
The EEC will only turn the pumps back on when it sees that the plugs are firing.
Sounds like you have a bad EEC, as even if you had an electrical problem with the Fuel System not shutting off it would still run.
The pumps do not run until they pressurize the system.
Have you put a gauge on it?
The pump will only run for two seconds and then the EEC will turn it off.
The EEC has no idea of what the fuel pressure is.
The EEC will only turn the pumps back on when it sees that the plugs are firing.
Sounds like you have a bad EEC, as even if you had an electrical problem with the Fuel System not shutting off it would still run.
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New User
Joined: Jun 2006
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I have yet to put a guage on it (maybe when the rain stops up here in NJ) but I can hear the pumps running when I turn the key to the on position but they never turn off. I'm unsure what turns them off. My buddy's truck cyles the pump for a second when the key is turned on, mine cycles on and never off. Your point about the EEC makes sense, that the truck should still run with the pumps on, the EEC may very well be the culprit. I guess I should put a guage on it first, what should the fuel pressure be?
Fleet Owner
Joined: Aug 2005
Posts: 23,667
Likes: 301
From: Easton,Ks
Hearing the pumps run does not mean they are not pumping OK.
With the key on and pin #6 of the Test Connector grounded the pressure should be 52 to 55 psi.
Sounds like you may not have to ground it on yours.
With the key on and pin #6 of the Test Connector grounded the pressure should be 52 to 55 psi.
Sounds like you may not have to ground it on yours.
Mountain Pass
Joined: Feb 2003
Posts: 136
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I am going through the exact same thing you are(Fuel pump not shutting off and not allowing truck to start). I do believe that it is the ECM, I however, have not bought a new one yet. I had a bad ground, that I repaired, but still the problem persisted. There are three grounds to the ECM you can check. They are on pins 20 40 and 60. And reading the wiring harness(Not the ecm itself) to ground should read under 5ohms. You can go to fordfuelinjection.com for a good write up on it. Let me know if you replace yours and it works. I will probably be replaceing mine(ECM) in the next few weeks.
