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ASEMaster35yrs
ASEMaster35yrs, Master Auto Tech
Category: Ford
Satisfied Customers: 2032
Experience:  ASE Certified since 1972,Master Auto tech,Heavy Truck,worked on all makes and models
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i have 1986 ford f150 5.l fuel injected. Start great runs fine

Resolved Question:

i have 1986 ford f150 5.l fuel injected. Start great runs fine idling but acts like it gets no gas when i accelerate. I new fuel filter, new cap and rotor, new coil & pu assemb., neew plugs. Now we are checking the fuel pumps ( dual tank ). what is the psi at the fuel rail ? we're getting 30psi. Is this the problem or could it be the reservoir, or the actual pumps and how do i tell which one ?
Submitted: 2 years ago.
Category: Ford
Expert:  ASEMaster35yrs replied 2 years ago.

ASEMaster35yrs :

Glad to be of help. This could be either fuel pump or pressure regulator. If it does this on both tanks, I would suspect pressure regulator.

ASEMaster35yrs :

The problem is definitely fuel related. 30 lbs is too low. Any lower and it would not run.

ASEMaster35yrs :

The fuel pressure regulator is located on the fuel rail on the lower intake manifold. (see diagram below)


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ASEMaster35yrs :

Pull the vacuum line off the fuel pressure regulator. If there is gas in the line, then replace the regulator.

ASEMaster35yrs :

Pressure should come up 8-10psi if you pull vacuum line off regulator. If there is no change, replace regulator.


 

ASEMaster35yrs :

I'm switching to Q&A format to be notified of your response.

ASEMaster35yrs, Master Auto Tech
Category: Ford
Satisfied Customers: 2032
Experience: ASE Certified since 1972,Master Auto tech,Heavy Truck,worked on all makes and models
ASEMaster35yrs and 7 other Ford Specialists are ready to help you
Expert:  ASEMaster35yrs replied 2 years ago.
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Expert:  ASEMaster35yrs replied 2 years ago.

Your problem may be the high pressure pump located on the left frame rail. Check pressure directly at the high pressure pump outlet port. If you still have 30psi at high pressure pump outlet port, replace high pressure pump.To check individual in tank pumps, check pressure at the source coming from the tank. you will need an in line tester.

The 86 had three fuel pumps. A single, low pressure pump in each tank and a third high pressure pump on the left frame rail. . It is the pressure delivered by the in tank pump that "decides" which way the changeover valve directs fuel.... If one in tank pump fails, the valve will not change tanks when commanded and the high pressure pump will still draw from the "good" tank even though the low pressure pump in that tank isn't turned on. If the pump in the tank you are running on fails, the truck will continue to run until that tank is empty. You will be able to change to the other tank

but not be able to change back. Here is a diagram of your selector valve in case you need it. http://ww2.justanswer.com/uploads/kennyz1963/2011-04-01_022533_1.pdf

Customer: replied 1 year ago.

I'm sorry it is taking so long for us to figure this out, new regulator put on and new pump was still only getting 30psi after regulator. new pump on and 0 psi. the change over valve ? rubber pieces disolving?? Is this the problem??
i'm beginning to wonder if this is why this truck only had 74,000 miles on it when I bought it 4 mo. ago.

Customer: replied 1 year ago.
,

I'm sorry it is taking so long for us to figure this out, new regulator put on and new pump was still only getting 30psi after regulator. new pump on and 0 psi. the change over valve ? rubber pieces disolving?? Is this the problem??
i'm beginning to wonder if this is why this truck only had 74,000 miles on it when I bought it 4 mo. ago.

Expert:  ASEMaster35yrs replied 1 year ago.

Are you checking pressure at the rail port or at the pump itself? Did you check pressure at both tanks? If you have 0 pressure after installing new high pressure pump you are either checking at wrong port,connecting at wrong port, no power to pump or new pump is defective. You need to check at the pump itself first before checking at the rail to see where pressure is lost. If you have good pressure at the pump but none after selector valve, then the problem would be at selector valve but if there is no pressure at the pump the problem lies there, not the selector valve. Did you check for power at the pump? Does the pump run? Check inertial switch to make sure it's engaged.

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