Fuel pump failures

[Airtech7]

I have a 1984 F250 460 with dual tanks. I acquired this truck with the rear fuel pump not working. I then replaced the pump while adding the high capacity tank. The pump failed in about 5000 miles, and I have changed it since.

The forward tank pump has failed twice, & I'm am preparing for another pump change. I have used carter pumps for all replacements. I am getting very good at replacing in-tank fuel pumps on 1984 F250 trucks.

I would think something is causing these pump failures. I have replaced both fuel relays, the tank switch valve, the tank caps, and the selector switch. When the respective pump goes off line, I can always switch tanks to remedy the situation, like running a tank dry. I drive a few miles, then I can switch back to the problem tank, only to have the whole scenario repeat after a few miles.

Any ideas?

Thanks for your time

[Gary Lewis]

Welcome!  Glad you joined.  

However, you apparently missed the email that Jim sent you asking you to make your first post in New Members Start Here folder.  We do that because we have the guidelines there and since we will hold you to them we want you to have had an opportunity to read them.

So once you've done that come back here and we'll discuss the fuel pump issues you are having.  And, don't worry - this happens frequently and we recover from it.  

[ArdWrknTrk]

Gary, can I tell you again how borked up the joining process is?  

Airtech, are you using the original harness?
Because if you aren't, and you don't have a resistor wire in 'Run' the pumps are going to die in short order.

https://www.garysgaragemahal.com/electric-fuel-pump-control.html

[viven44]

I was going to blame his new selector valve (again ) and ask him to bench test it with a battery and vacuum hose. I will need to make a video on how to do this, as I have both a good and a bad selector valve.

With my trials, it is my belief that the resistor wire is a fuel pump cut-off safety/current-limiter specific to this implementation. I am not sure why some bullnose fuel pump implementations call for it while others don't.

It is my belief that if the selector valve isn't behaving the fuel pump will be "choked". When it is choked the current draw increases. When this happens a few times the pump's lifespan is reduced greatly.

I had a current clamp meter to read current draw readings during all this. When the pump was happy and running well, the draw was ~1-2A. When the pump was choked or if it was close to end of life, the draw increased to >4A. When the current draw went up, there was significant voltage drop at the resistor which cut-off the pump. When I bench tested my selector valve the supply line to that specific pump was not in the correct spot. All I had to do was get rid of my selector valve and replace that pump, so far so good. Didn't need new relays or change in wiring.

Maybe do the following in his case
- Factory wiring in place ? If not add resistor to it. I do agree that a resistor wire would save the pump in a 'choke' scenario, without it might take only 1 choke. As quickly as his pumps are dying, it might be that he has 2 different reasons why they are dying quicky. Fuel pump is Choked and then Fried.
- If the bench test of his selector valve proves that the valve is behaving, the next step is in-situ testing of the valve.
- Check resistance between fuel pump harness and fuel pump relays for both pumps

Edit: maybe another function of the resistor is to limit maximum current / therefore fuel-pressure ???

[ArdWrknTrk]

'splain to me the resistor wire in 460 SINGLE tank implementations.



If the valve switches, it works..

Edit: it doesn't limit fuel pressure, that's what the vapor separator does, and why there are different orifices available.
The pump is like the ignition coil (wound tighter than a ducks butt) it can handle battery voltage while cranking but it isn't meant to run that way.

[viven44]

Jim, I knew you were going to point that out. The only possible guess is that it doesn't play a role in a single tank system but Ford decided to keep that wire because it didn't hurt anything... I just can't think of why those fuel pumps are special needing a resistor wire vs. every other pump that you install.

Resistors are current-limiting devices so there is clearly a need to limit current for something. Only reasons I could come up with is maximum fuel pressure or safety.

BTW, where is the vapor separator in that system ?? Is that part of the return-line seperator-deal up near the water pump?

[ArdWrknTrk]

That's exactly what makes Hot Fuel Handling recirculate cool fuel from the tank up through the scorching engine bay.

Can you not draw a parallel with the ignition coil?

Remember, this is all coming from the same (highly paid) staff of automotive engineers at Ford.
They were making 10x the wage you mentioned... Back then.  😳

[ArdWrknTrk]

Is there a reason not to wind an ignition coil for 14 volts?
Maybe the battery is taking a hit while you crank the starter?
Maybe they had no means of boosting voltage, but they had an easy way of limiting current?

[viven44]

Makes sense! I don't think the resistor is a precise pressure regulator by any means.. it was just a random could-it-be thought. Didn't realize the vapor separator (as I know it now) had an orifice either, just thought it was funny looking return line contraption.

[ArdWrknTrk]

There are three orifices available (coded Red, White and Blue!)
40, 60 & 90 thou I believe.

Depending on how much recirculation you need.
The in-tank pump is pressure limited.

[viven44]

Thought I knew this system, but apparently not well enough

If original poster comes back, hopefully he finds things to follow upon. He seems to know his system well already as he has tried several things.

I have been on forums where I posed a question only to never show up again  yes I have been that person... I had a discussion on that one topic... but then those were vehicles I didn't care much for as well so I was done after that one issue was resolved..., so I think if we want bullnose nuts here, it will naturally work itself out. The nuts will stay

[Ifitaintbroke]

This nonsense is why I went with a mechanical pump.

[viven44]

I still use the in-tank pumps and haven't had issues since going to the manual selector valve. I believe the one pump that died only died because of the bad selector valve. This is the replacement pump I used

https://www.amazon.com/gp/product/B000CGFUNE/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Currently, I have ahead of the vapor separator a metal in-line fuel filter, fuel pressure gauge. I always see ~4-5 PSI pressure.

I do agree a mechanical fuel pump further reduces variables however there is more redundancy built in the system with 2 in-tank pumps that's why I haven't deleted them. I did have my doubts though.

[ArdWrknTrk]

Mechanical pumps can't prime the carb, and they suck if you let one tank run out(remember my gauges didn't work at all with Metermatch)
But I am adept at noticing fuel starvation and very quick to flip the switch!

Electric pumps worked in millions of trucks for billions of miles.
Don't mess with success...

[Ifitaintbroke]

Why can't they prime the carb? It pumps fuel while the engine is turning over.

[ArdWrknTrk]

It doesn't really function the same way a pump submerged in the fuel does.

It takes a LONG time for a mechanical pump with no prime to suck from 16' away

[mat in tn]

they are designed to keep up and not really to catch up. you can run a battery down trying to get a dry line set full again. this is why we fill carbs manually on new startups.

[ArdWrknTrk]

A horse syringe into the vent tube works every time!

Jeff in Quebec doesn't understand the difference between winter and summer gasoline. (at least they don't have some corn farmer -read BIG AGRA- subsidy up there)

[viven44]

I like the little tip I learned from my father-in-law. I used to remove the air cleaner and pour fuel down into the carb to start my sitting truck. He told me to just loosen the wing nut a couple turns and pour the fuel on the threaded stud, which of course is going to guide fuel down where it needs to go. I wondered why I didn't think of that before.

[ArdWrknTrk]

My air cleaner lid is domed (to shed water)
Maybe I'm not reading this right, but the rubber washer under the wingnut usually sticks to the lid.

I pull the (non-existent) A.I.R. Pump inlet plug from the passenger side and spray a shot of ether onto the filter element.

Or, I take the lid off and fill the bowl through the vent tube.