I took it in and they diagnosed it as a fuel pump, replaced it three times now and still no different.

Is there a wiring diagram for this thing I can go off of?

I checked continuity between the + and - wiring going to the fuel pump and got great continuity between them--- Could this be the issue? what else is this wired too?

 

Am I correct as this is an EFI motor?

I'm not sure what you mean by you have great continuity between + and -. Are you checking the leads going to the pumps or from the power supply?

Need to know more about your truck and the symptoms.

Runs great then just stops like you turn off the key? EFI or carb?

 

EFI trucks have an oil pressure sensor that provides a relay with power (actualy ground if I remember correctly) for the fuel pump, so if oil pressure is lost (e.g you have an accident and engine stops running but you can't turn ignition key off, fuel line is cut, etc., etc.) the fuel pump stops running. There is a relay under the hood to allow a couple of seconds of fuel pressure build/prime without oil pressure. Usually you can turn the key to run postion without starting engine and hear the pump run for a couple of seconds.

Possibly the oil pressure switch is going bad.

When the engine stops, will it immediately restart?

 

That's not correct. Ford did use a oil pressure switch interlock on their 460 carbed trucks with the electric pumps in the tanks, but their efi systems were hooked to the the main computer. The computer grounded the fuel pump relay wire and made the pump run. If the computer loses the pulse signal from the distributor, then it will shut down the pump as a safety. It assumes no pulse means the engine is not turning, even though the key is in run.

 

Sorry, I know better, lol. Working too much and wrote it when I was tired.

It's an 85 f150 2wd xlt lariat with the EFI 302, automatic transmission.

When it's cold, the truck will fire right up without hesitation. It will run fine for about 2-5 minutes depending on ambient temperature. It will then start to stumble like it's losing fuel pressure *pretty sure it is* and eventually will die from stumbling. It will immediately refire and you can keep it running rough for a little bit with the throttle, but it will eventually die out.


Fuel pump primes just fine, no worries there-- even when it's at its worst.

What I said earlier about continuity between the + and - wires--- It's the two wires that connect to that high pressure pump. I took my DVOM and measured to see if there was resistance between the two wires. The DVOM read exactly as it did if the two leads were pushed together, indicating that the wiring between the positive and negative wires (not fuel pump terminals) are connected at some point. Keep in mind this is with the keys OUT of the ignition, so maybe something internally within the relay when it's not being powered?


Oil pressure via dash gauge seems to be just fine. It's not even enough time for the fuel pressure to drop from viscosity change at operating termperature before it starts to die.

 

This is a computer-controlled engine, correct? Pull the codes, here's how:

Fuel Injection Technical Library » How To Run a Self-Test

 

 

Howdy,

I have had the exact same issue aswell and have found no solution
THanks,

-Matt

 

This thread came back from the grave. wow. I sold the truck not long after fixing the issue. The gas tank had all kinds of gunk and crud in it. When it was running, it would naturally all move towards the sock on the fuel pump. Enough gunk on the fuel pump sock and well, no fuel pressure. I cleaned out the fuel tank and put a new fuel pump in it. This solved the issue completely.

I'm not sure what I meant above by continuity between the + and - terminals - likely I was using a DVOM on the continuity setting and not looking to see how much resistance the fuel pump motor had. The fuel pump was in fact NOT bad, but I had already purchased the new pump. Old pump was pulling quite a few amps as the electrical connector on the pump had started to melt.

Had old gas in it, here's the old pump - was pretty crusty!

 

Q.man, thank you for letting us know what your fix was, it may help others.

I would think your high "amp pull" could have been from the pump trying to pull fuel thru that junk.
Also fuel helps cool the pump so if it was heating up that would also make it pull more amps.

If people with this issue ran a fuel pump pressure test and it was a pump issue the psi would drop off.
Just make sure the test gauge is installed good, you don't want it to disconnect and spray fuel all over and cause a fire.

Again thanks.
Dave ----

 

Absolutely agree here, and all of the above were an issue to some degree.
I'm not entirely sure there. I was measuring pressure at the fuel rail and could watch the fuel pressure drop off as the main high pressure pump was starved of fuel since flow didn't exist anymore from the in-tank pump as the sock got clogged.

I expect that the pumps were not good as new, but they still did work. I'm sure if I had just cleaned the tank and put a new sock on the pump it would have worked the same.

 

My point was if it was a fuel issue, bad pump(s) or junk starving the pump(s) the pressure would drop off so you would know where to start looking for a fix.
Junk in the tank(s) covering the pickup / sock is hard to see with out a fuel pressure test as you cant really see inside them.
Dave ----