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1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks Discuss the Early Eighties Bullnose Ford Truck

1986 f-250 electrical/fuel pump problem

 
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Old 04-23-2011, 02:01 PM
bsw710
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1986 f-250 electrical/fuel pump problem

Hello,
I've got a 1986 f-250 460 auto with an electrical problem. There is a plug on the drivers side with two wires going into it and one coming out that seems to have something to do with the fuel system. One of the wires which looks like its pink is getting very hot and shutting down the truck. It runs from the single prong plug to an ignition relay on the firewall that I just replaced thinking that was the problem. I also replaced the ignition module mounted on the fender. I unplugged the plug and started the truck and the truck ran for a minute and died. It ran until the fuel was gone out of the carb. I don't know where to go from here. Any help is greatly appreciated.

Thanks, Brian
 
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Old 04-23-2011, 10:59 PM
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You might have a fuel pump problem if the wire is getting hot. This system is rather complicated and is always a problem on the 460's. Here's a diagram.



If you trace the diagram out, you will see the pumps get power directly from the starter relay during cranking, but then get power from a oil pressure activated switch for normal engine operation.
 
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Old 04-24-2011, 01:31 AM
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Fuel Pumps problems on these trucks are a common problem. I after replacing both in tank pumps, I ended up installing an Electric Fuel pump just forward of the fuel selector on the frame. I use a 14 psi pump with a pressure regulator. The best deal on electric fuel pumps like mine are from Skip White on Ebay. I think I paid $38 for a no name pump that is a Holley knock off. It works great & a friend of mine that drag races & runs street Hi Pro cars uses them & several items from Skip White Performance from their Ebay Store. Excellent service, I had some questions as to the size of the pump because I wanted it to fit inside my frame They emailed me back the info the next day.
Craig
 
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Old 04-24-2011, 07:12 AM
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Thanks for the information. I thought it could be a fuel pump problem but I wasn't sure. Can I install an external electric fuel pump without removing the pump in the tank or will it block the fuel flow?
 
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Old 02-18-2015, 11:59 PM
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I'm Having a Problem with my 86 similar to yours, I to have the 460 and the fuel pump is mounted on the Drivers side Frame rail. I pulled the Plug on the Pump and i put a tester in the Plug holes and only one has any sign of life and it flashes slowly On and Off, I have reset the Safety Reset Switch and still nothing, Is there also Pumps in the Tanks?
Thanks, Sorry for taking advantage of your Questions I learned a Couple Things Thanks!
Jon
 
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Old 02-19-2015, 03:03 PM
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That's not a pump on the frame rail. That's the fuel tank selector valve. The flashing voltage is coming from the fuel gauge in the dash. The selector valve switches the sending units for the guage.
 
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Old 02-19-2015, 06:02 PM
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So are the pumps in the tanks?

Originally Posted by Franklin2 View Post
That's not a pump on the frame rail. That's the fuel tank selector valve. The flashing voltage is coming from the fuel gauge in the dash. The selector valve switches the sending units for the guage.
so I need to check voltage back to the tanks then right?
thanks for the help too
 
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Old 02-20-2015, 02:38 PM
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Factory pumps are in the tanks on the 460's if they don't have a mechanical pump on the engine.
 
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Old 09-23-2016, 11:39 AM
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Hey guys, I am new to the site but I have the same truck (1986 f-250 460 automatic). I bought it cheap with previous owner claiming it needed a fuel pump. The truck cranks and when I poured a little gas into the carb it fired right up. I assumed he was right so I stuck a fuel pump and sender assembly in the front tank. I hear nothing when I turn the key on and still no fuel. I guess I should have looked into it more before doing so. Does anyone have advice on where I should start from here? I have the bed off so it is easy to get at both tanks and lines/wiring. Thanks for any help!
 
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Old 09-23-2016, 12:07 PM
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Pump power comes from the fuse panel to the inertia safety switch in the passenger side of the cab.
Then to the fuel pump relay, then to the tank selector relay (near the drivers side hood hinge.

Since you do not seem to have the pump priming while the starter is turning, i would say it is the selector relay... or past that.

Im on my phone, so you do a forum search for "hot fuel handling"
This will turn up troubleshooting and wiring diagrams.
 
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Old 09-23-2016, 12:44 PM
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See that pink/black with the 20 gauge blue fusible link at the top of the the diagram below? That should be going to your "I" terminal on the starter solenoid. Take that wire off and touch it to the large terminal on the starter solenoid that goes to the battery +. Do you hear the pump running? Will the engine start now?

 
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Old 09-24-2016, 01:42 AM
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Dave has put you on the right track but you don't want to hot wire the fuel pump because the system is not designed to run on a full 12 volts. The main fuel pump circuit has a resistor wire to step down the voltage. It's okay for testing but not long term.

First check the fusible links at the starter solenoid. Fusible links are wires designed to burn up before your wiring does and that's why you really want to use them. If for some reason they burned up you got no power!

The bypass wire that belongs on the I terminal should start with about a 3" length of 20 gauge fusible link. And the main fuel pump power supply is a big ring terminal attached to the big hot post on the starter solenoid. It too should have about a 3" section of fusible link before it's spliced into the main wire.

From there power passes through the inertia switch and then to the fuel pump relay. **** So if you want to check the circuit you should have power from the starter solenoid to the fuel pump relay hot all the time.****

Once you've figured out where the fuel pump relay is you can try a new one. They're not very expensive.

After all that's squared away check the oil pressure switch circuit. Start with the fuse (#18?) and make sure it's good. Then check to see if you have power at the oil pressure switch. It is located at the back of the motor, on top, below the can shaped oil pressure sending unit (if you have one). It you disconnect the plug one of the wires should be hot with the key on. **** if you jump the oil pressure switch with a jumper wire THEN the fuel pump should run with the key on even if the motor isn't running**** but If you have to defeat the oil pressure switch to get the fuel system to operate you either have a bad switch or no oil pressure.

Note: the pumps do not run or prime when you turn the key on. The fuel pump is only supposed to run when the starter is engaged or the motor is running.

And that's about as far as I go. Beyond that there's a mess of dual fuel tank switch gear fun that I am unfamiliar with.
 
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Old 09-26-2016, 11:28 AM
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Thanks for the input guys. I was away over the weekend but will put some time in on it this week. On a side note, does anyone know of a straight forward way to delete the rear tank from the fuel circuit? If it was easy enough I would do that and simplify things.
 
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Old 09-26-2016, 11:41 AM
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The rear tank is 'default', as in if the selector relay loses power everything switches to the rear..

What's real odd is that you don't have the pump running while the starter is engaged, as this bypasses *both* safeties *and* the fuel pump relay.
 
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Old 09-27-2016, 07:51 AM
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Originally Posted by tmeckes03 View Post
Thanks for the input guys. I was away over the weekend but will put some time in on it this week. On a side note, does anyone know of a straight forward way to delete the rear tank from the fuel circuit? If it was easy enough I would do that and simplify things.
You will have to find the valve on the frame, find the two lines going to the engine and the two lines going to the front tank. Take these lines off and splice them together. Usually the return line is the smaller line. You will have two lines left that go to the rear tank, plug them with something.

Also at the valve is the sending unit wiring. Using the diagram above, you will have to cut the wire going to the front to the gauge, and cut and splice it into the sending unit wire going to the front tank.
 

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