Fuel pump not working

Tiny
MHJ2756
  • MEMBER
  • 1994 FORD F-150
My truck will not start. I am sure it is fuel delivery problem. It has dual tanks 5.0 engine. I do not have any power at the front or rear tank connectors, rear tank has never work their is no power at the selector switch or at the inertia switch. There are four relays mounted next to the power distributor box. I change them around, I checked all fuses. I also grounded the lead of DLC connector had the same problem. One other time I keep turning the ignition off an on until I heard the fuel pump come on. Thanks if you could help me with this problem.
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Wednesday, October 15th, 2008 AT 2:55 AM

57 Replies

Tiny
JAMES W.
  • MEMBER
Do you have battery voltage at fuel pump relay socket? Can you hear the fuel pump run for just a few seconds when you turn the key to "on"?

Here is a guide to help you test to see where you are losing power along with the engine and fuel pump wiring diagrams so you can see how the system works:

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

I have seen the fuel pump switch valves also cause this problem FYI.

Check out the diagrams (below). Please let us know what you find. We are interested to see what it is.

Cheers
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Wednesday, October 15th, 2008 AT 3:35 AM
Tiny
MHJ2756
  • MEMBER
There are four relays I think I have 12 volts at all of them. I cannot hear any noise from the fuel pump. Also, I have replaced the ignition switch.
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Wednesday, October 15th, 2008 AT 6:02 AM
Tiny
JAMES W.
  • MEMBER
I am sorry, but "thinking" you have power to the relays does not do me much good. Let's do it this way.
One of the relays of the four will have the following color wires. My diagram does not tell me which one for sure, but look for these colors. These are the wires going to the relay socket.
1- Yellow-12 volts from the fuse. No power, the fuse is out.
2- Dark green/yellow-power to inertia switch. From inertia switch to fuel tank selection switch, then to fuel pumps.
3- Red-12 volts from computer when key in "start"position. Not "run", start position.
4 Blue/orange-ground from computer with key in "start" position.
Test; jumper wires 1 and 2. You should now have power to the inertia switch, the sector switch and which ever tank is selected, that pump should be running.
If not, check power at fuel pump connection at tank. If you have power there, the pump is bad.
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Wednesday, October 15th, 2008 AT 8:58 PM
Tiny
NATASHA30122
  • MEMBER
We are having the same problem on our 1994 Ford F150 single tank. No firing and no fire to the fuel pump. Please respond where the fuel relay is located. Is it under the hood or in the truck? Which relay is it? Thank you! Robbie C.
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Sunday, October 26th, 2008 AT 2:52 AM
Tiny
NATASHA30122
  • MEMBER
I had to replace the switching valve like you said everything working great now. :)

Thank you so much for your help.
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Sunday, October 26th, 2008 AT 2:55 AM
Tiny
KEN
  • ADMIN
These trucks had a big problem with the switching valve which is located between the tanks on the frame rail on the drivers side.

Please let me know how it goes, we are here to help.

Best, Ken
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Tuesday, August 16th, 2016 AT 9:35 AM
Tiny
RACE STREET
  • MEMBER
I have been trying to figure out why my rear tank quit working. I just replaced it then a week after it cut out on a hard turn. Front tank works. Replaced relay and inertia switch. I cannot hear pump come on either.
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Saturday, July 28th, 2018 AT 11:43 AM
Tiny
STEVE W.
  • EXPERT
RACE STREET Could you please use this link https://www.2carpros.com/questions/new
and ask this as a new question, please give all the information you can as well as what you have done to try and repair the issue. Thank you
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Sunday, July 29th, 2018 AT 7:37 AM
Tiny
BU3322
  • MEMBER
  • 1994 FORD F-150
  • 6 CYL
  • 2WD
  • AUTOMATIC
Front fuel pump not working put in new pump not working no power to plug at fuse box have power on both side of fuse with key out of truck what to try next?
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Friday, May 29th, 2020 AT 11:40 AM (Merged)
Tiny
CADIEMAN
  • MEMBER
Test the ground and recheck the maxi fuses under hood.
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Friday, May 29th, 2020 AT 11:40 AM (Merged)
Tiny
BU3322
  • MEMBER
The back tank works and maxi go still do not have power to the front tank the switch for front to rear is go!
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Friday, May 29th, 2020 AT 11:40 AM (Merged)
Tiny
CADIEMAN
  • MEMBER
Check the fuse links at the starter
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Friday, May 29th, 2020 AT 11:40 AM (Merged)
Tiny
WILL12463
  • MEMBER
  • 1994 FORD F-150
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 80,567 MILES
- EEC IV

I have a 1994 Ford F150 XL With a problem I see several people are having but no solution. This is my Fathers truck, owned since new and it sits in the garage quite a bit.

Truck will not start.
It has dual tanks.
With ignition on, engine not running, you can hear the fuel pump running continously. It normally shuts off shortly after turning the key on. (Builds pressure then stops until start or pressure drops)
I switch from front tank to rear, not running with ignition on, both pumps do the same thing, each run continously but vehicle will not start.
While looking under the hood with key on, engine off, the fuel pump did stop. I turn key to start and truck ran fine until I shut it off. Then same thing. Pump runs continously, either front or rear, will not start.

I have replaced fuel pressure regulator thinking it was always open. That did not fix the problem.

I replaced fuel filter. No go.

I have disconneted powertrain Control Relay, key on, pumps stop running, won't start.

I have disconnected Fuel Pump Relay, And PCR, Replaced, No start. (Saw this on a post)

Lastly, CEL is on, jump diagnostic plug, and CEL stays on, does not flash code.

I have been able to get started working the throttle, no power from engine, undrivable.

I have reviewed more postings and found others with the same problem. One suggestion was to change both pumps. "One pump relies on other to work properly". As I understand it, I have two tanks, each with thier own pump. Pressure lines join at fuel line "manifold" inside left frame rail, then into a single fuel filter. I assume a check valve(s) inside the fuel pump keeps fuel from going through when the other pump is on, same for the return fuel lines. Can you explain how one of these fuel pumps (check valves.)Fails that niether pump will build pressure?

I'm stumped, please help.

William
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Friday, May 29th, 2020 AT 11:40 AM (Merged)
Tiny
KHLOW2008
  • EXPERT
Hi will12463,

Thank you for the donation.

Fuel pump has in-built one way valve that prevents fuel returning to the fuel tank from the pump that is not working.

Check the fuel pressure with ignition switch turned on and off several times to ensure it is withn specs.

The CEL not blinking any codes indicates either it is faulty or has wiring faults, more likely the former.

When ignition is turned on, the fuel pump would prime for 2 to 3 seconds and turn off, not because pressure has built but rather it is timed to cut off by the PCM. The fuel pump is not designed to cut off when power supply to it is available as the fuel pressure regulator would control the pressure and allow excessive pressure to return to tank. For in-tank fuelpressure regultaor it would flow out of the pressure relieve hole into tank, for those equipeed with return hose from the pressure regulator, the return hose would allow that.

As the fuel pump is not cutting off, it indicates the PCM is not performing correctly. When this occurs you are not able to start, confirming the PCM is suspect.

You are most likely looking at a PCM that is intermittently failing.
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Friday, May 29th, 2020 AT 11:40 AM (Merged)
Tiny
WILL12463
  • MEMBER
Great responce and quick too!
So, the pumps are controled by the PCM and not some type of pressure switch. Truly that should have been obvious.

YOU: "The CEL not blinking any codes indicates either it* is faulty or has wiring faults, more likely the former."
ME: Is it* the PCM?

So the fact that the pumps are running when they shouldn't be, is a PCM issue, possibly why CEL just stays on during diognostics, (no voltage pulse from meter pin). It is all making so much sense!

There are problems with the 1990-1993 F150s. Fuel being transfered from on tank to another, fuel pump regulator failing closed, breaking check valves, causing fuel to be transfered into the tank not being used, overflow, creating safety and enviroment issues, bla, bla, bla.

THIS IS NOT THE SAME ISSUE! I've read folks replacing relays, would fix it for a day, a month. Replacing both fuel pumps, do it again in a couple months.

INTERMITTENT PCM FAILURE! That's it! Because the pumps are running when they shouldn't be! PCM is the only thing that will turn the pump on! CEL is on but can't get diognostics to work.

You the Man!

Thanks, I'll let you know if we're right, but how could we be wrong! (Famous last words)
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Friday, May 29th, 2020 AT 11:40 AM (Merged)
Tiny
KHLOW2008
  • EXPERT
" YOU: "The CEL not blinking any codes indicates either it* is faulty or has wiring faults, more likely the former."
ME: Is it* the PCM? "

Yes, I meant the PCM.

" Thanks, I'll let you know if we're right, but how could we be wrong! (Famous last words), "

That is the kind of attitude that makes the world go round in a cheery mood.

Remove the PCM cover and check for signs of stains on the printed circuit board that are most likely caused by leaking capacitors. They are the usual cause of intermittent PCM failure.
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Friday, May 29th, 2020 AT 11:40 AM (Merged)
Tiny
WILL12463
  • MEMBER
So there is a conclusion to my initial question and advise, I want to report the results. I did remove the PCM. Looked inside the PCM and yes, capacitors did show signs of leaking. I was not ready to take on fixing the board, especially with all the clear coating on entire board. I have seen folks do this to install new flash memory, speed improvements. I wanted to get this done! So I ordered a new reman from Autozone, $244 the cheapest I found with a warrenty.

Removing the PCM was a pain! Jack up the front left wheel, remove wheel, remove all body screws holding the plastic inner field, move inner fender to gain access to the PCM on the left firewall. Remove bolt in PCM to take off wiring harness, remove two nuts and rubber seal. Pull out PCM.

Installed new PCM and all is good. If I have additional problems, I'll update, If this is the last you hear from me, than all was good.

Thanks CarPros,
VERY GOOD ADVISE! If I followed my internet research, I would have continued down the wrong path. Only spent $100 more than I should have with what I thought was the obvious solution

You folks are great, worth every bit of my donation!
William
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Friday, May 29th, 2020 AT 11:40 AM (Merged)
Tiny
KHLOW2008
  • EXPERT
Good to know you have positive results.

Thank you for using 2carpros and have a great day.
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Friday, May 29th, 2020 AT 11:40 AM (Merged)
Tiny
SCILEPPI
  • MEMBER
  • 1993 FORD F-150
Electrical problem 6 cyl Two Wheel Drive Manual 192500 miles

I just bought this truck and on the way home I stopped and when I went to start it, it would not turn over. It is an I6 4.9 rear tank, single tank. Has spark believe it to be a fuel issue. The engine will crank but not turn over. Removed the intake and used ether and it will start. Changed the fuel pump with 2 new pumps, filter, electrical pig tail, relay and checked fuses. After I changed the pig tail truck started and ran for about 10 miles, Stopped at stoplight and truck quit. Would not start. Don't know where to look next. Tested the inertia switch. Switch tested good. Any ideas?
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Friday, May 29th, 2020 AT 11:40 AM (Merged)
Tiny
RASMATAZ
  • MEMBER
Does it come on for a few secs when key at run position? If not check the fuel pump relay if it comes on check whether the injectors are pulsing while cranking engine over.

Here is a guide to help you see where you are loosing power

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

Here is the fuel pump wiring diagrams and engine controls so you can see how the system works.

Check out the diagrams (Below)

Please let us know what you find.

Cheers
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Friday, May 29th, 2020 AT 11:40 AM (Merged)

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