1987 F250 SC, 460, carbed, C-6, 4.10 rear. When I bought the truck previous owner said rear tank gauge was not always working. Dropped the tank, got a new tank, pump/sending unit. Put everything back, worked fine for about 3000 miles. Then the rear pump stopped working. Go through all the trouble-shooting procedures. By-passing relay etc. Dropped tank, put in new pump (of course tank was full). 2 months later hit a bump in the road, fuel gauge reads over-full all the time, rear tank again. Drop tank again, replaced pump/sending unit (wire came off - who knows why, looked like end was bent at the factory). Today truck wouldn't start on rear tank, about 75 miles/ 2months on new unit. (Don't drive 6-10 MPG truck that much).
It's a PITA to drop the tank. Have to drop the class IV hitch, remove air shock lines and move the exhaust over a bit. As well as the other stuff. I use gas additive, Techron. These have all been NAPA/Carter pumps and replaced under warranty. Any ideas?? I'm all out of them. Thanks

 

Had a '87 F150 and went through 5 units in the rear tank, 4 under warranty. Poor design and quality from the vendor that supplied Ford. Dealer told me to rotate between tanks to solve the problem, I always used one tank then the other when filling up unless on a trip then both got filled and used.

 

Sounds more like a wiring ground problem then the pump. You are losing the ground to the tank. A open ground to the tank is what makes the gauge read passed full.
With no ground the pump will not run either. They are two separate systems using the same ground and the same hanger.

 

Thanks for the reply. Maybe this time will be the charm. This will be the 3rd replacement under warranty. Hope not to do a 4th. The truck does sit a lot due to mileage/gas prices and is used mostly for hauling/towing. Ford has a TSB out about occasional use of Techron to lube the pump. Am going to check into a Ford pump.

 

Hi Subford, when the gauge read overfull, it was due to the slip-on connector falling off inside the tank. Instead of being straight one side was bent so it didn't stay on too long and came off when I hit a bump. Pump was working. I will go back and check the ground connection, even run a wire from the battery if needed. I wonder if there could be a problem in the connector similar to the turn/parking light socket problem. Gas gauge is reading a little above 1/2 now. Thanks for the insight.

 

My 87 is having the same problem with Napa pumps but on the front tank. Im on the 3rd pump in less than 300 miles. I have been trying to get this truck to run right for over a year. I got her running pretty well to drive to a new house I moved into and now she is dead again in the driveway.

BTW - The rear pump and send also are not working.

Can I swap a better quality pump onto the Napa sender assy? If so what brand is best?

I have been pulling the bed. Is it easier to drop the tanks?

 

Whoa guys guys, you all have failed to mention another high possibility, my original pump lasted oh Idk about 16 years then it decided to die, well here comes replacement drop tank removed the lines attached to the tank all that PITA stuff. Well after being assembled the gauge would read full but the truck worked perfectly then hours later the gauge started working so that wasn't a problem. Here's the deal, your going through pumps like crazy other than wiring maybe the tank has way too much crap in it dirt or carbon idk what the hell it is but it gets created in there which probably caused the first one to go out. I just bought a new tank so it was as clean as could be.

 

I think lifting the bed is way easier, and I've never had trouble with aftermarket pumps maybe the design is cheaper therefore if its ran and it picks up the crap inside the tank it burns out way quicker, also I failed to mention on the other post, I too replaced the pump twice but the second time it wasn't the problem so first aftermarket unit was still working well oh and I got mine at autozone

 

2007F150FX4,
Maybe it is not the pumps.
The pump and the gauge are two different systems and only use a common ground. They use the same selector switch but they are on separate circuits through the switch.
You could also have a bad selector switch at the dash.

Lets start by what is the gauge doing.
Is it pegged out at one end or the other end of the scale?
Or does it move and point to empty each time that tank is selected and the key is turned on?

Can you hear the selected tanks pump run for one second and quit each time the key is turned on?
Does the frame pump run for one second and quit each time the key is turned on?
If none of the three pumps run at all do you hear the green bottom relay click each time the key is turned on and drop out one second later?

 

I totally forgot the older models had a frame pump also, yea exactly what mister subford said, if you can't make sure yourself just have someone else help you out to listen to the 1 sec whine. Bad switch selectors are very common and make you go insane no kidding

 

In my case, I installed a new tank with the new pump so dirt is not an issue. Truck only has the low pressure pump in the tanks (carbed not injected.)
Update: put another Napa/carter pump in. 2 cans of Techron. Drove to gas station off front tank, filled rear tank then switched to rear. Drove about 5 miles, parked it. Went to start it a couple of weeks later. Would not start on rear tank. !@#$%^&* Wiring checks out old pump run new one does not.
Carter tech told me to make a tester from a sealed beam headlight. Hook high and low beams together. Check across the battery to get an idea of intensity. Then go to tank plug in and compare intensity . He said the light will draw about 8 amps the same as the pump. Left it on for about 5 minutes showing no dimming. Tech said this would show a wiring/connection problem if one was there. This last pump went in for "dissection" the area rep has not returned calls so I'm going with an Airtex today. Did run another ground to the battery. Getting ready for a 1500 mile trip, so if this one quits, I'm going back to drinking.

 

VERY, VERY likely the case.

A switch that is FAILING and not totally FAILED will have these symptoms.

Listen to subford........he knows his stuff.

My .02 cents

Bob

 

Yes he does
In my case the pumps could be burning out if they don't have enough amperage to run . Hence the headlamp test as mentioned above. I hate just guessing and replacing parts. I'll pull the switch and see if I can find anything.

 

Subscribed so I can follow along. I have a problem in using the back tank also so I'll be reviewing when I get around to fixing it.

 

I see I gave you some wrong information as I thought you had a FI engine.
It could still be the dash switch as what I said above goes for yours also.
Here is an 1986 diagram as I do not have any information on an 87 with that set up but I think a 1987 is the same as a 1986 so here is the diagram:


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