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Category: Ford
Satisfied Customers: 26645
Experience:  ASE CERTIFIED TECHNICIAN ADVANCED LEVEL SPECIALIST. Wisconsin certified emissions state inspector
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I'm hqving wierd fuel pump issues with my 1990 ford f150. I

Customer Question

Hi! I'm hqving wierd fuel pump issues with my 1990 ford f150. I Have dual pumps/tanks and my fuel pumps intermittently and at what seems like complete random, do and do not have power.
JA: Have you ever replaced the fuel pump, or is this the original?
Customer: I recently got the truck, so I do not know. I'm guessing it may be the origionals. but the problem is consistant in both pumps, on and off. which makes me think its a wiring short or something I Just replaced the EEC and fuel relays no change. it will start and idle sometimes (fuel pumps audibly come on when the key is turned on) but will die after about 5 minutes of idle, then there will be no fuel pump activation with the key
JA: Are you fixing your F150 yourself? What have you tried so far?
Customer: yah i am. I have replaced both relays and checked the collision shut off switch under the dash. there doesn't seem to be an issue there.
JA: Anything else you want the mechanic to know before I connect you?
Customer: when i test the EEC relay harness at the computer control wire, I do not have any voltage with a test light when the key is turned on. power to the pumps/ EEC relay when I turn the key seems intermittent , so i suspect wiring? I would just like another opinion. thanks
Submitted: 9 months ago.
Category: Ford
Expert:  AMEDEE replied 9 months ago.

Hello and welcome!

My name isCustomerand I can assist you with your question.

Expert:  AMEDEE replied 9 months ago.

I will try my best to answer all of your questions.

However, before we get started, please let me mention a few things.

1. If at any point you would like to speak on the phone, please feel free to request a phone call on your end and I can call you right away.

2. If you dont understand any technical terms or anything that I mention (component tests or theory or operation), please let me know and I will provide you with a more in debt explanation or answer.

3. Please understand that I am here to help you anyway I can.

Not only I can give you my opinion on what is going on, but I will help you diagnose the problem. However, I need your VIN number please.

Thank you!!

Customer: replied 9 months ago.
Expert:  AMEDEE replied 9 months ago.

Thank you for the VIN!

We are going to need to check for power going into and coming out of both the inertia switch and the fuel tank selector switch to see where we are losing power on the fuel pump circuit affecting both fuel pump when this condition occurs.

The power wire going into the inertia switch is brown. The wire leaving the inertia switch is pink/black and then turn into a red/yellow wire before going into the selector switch.

Here is a wiring diagram of this circuit. Let me know!

Customer: replied 9 months ago.
I will check that asap, thank you. Do you know where the selector switch is located ?
Expert:  AMEDEE replied 9 months ago.

Its the switch where you select which fuel tank you would like to use. Do you see it inside the vehicle?

Customer: replied 9 months ago.
Oh, yah I thought you meant the in line fuel Selector valve between tanks for some reason. I know where the switch is.
Customer: replied 9 months ago.
I'll be able to check that tonight
Expert:  AMEDEE replied 9 months ago.

Sounds good!