1986 Truck - Fuel Pump???

Feb 24th, 2003, 03:50 PM

My 1986 truck just quit running. A quick check revealed no fuel getting to the carb. I had recently had a tune done where they not only replaced plugs and wires, but put on a new fuel pump and filter as well. I took the output line off the pump and watched it and it pumps sporadically. I was told that it could be the pump relay???(can't seem to find it) In an effort to bypass the relay I ran a wire straight from the battery to the pump. Again the pump is sporadic, and now I'm told it's a "pulse pump" and that's normal. Bottom line is that I'm still not getting fuel up to the carb. I even ran another hose incase mine was clogged. Any thoughts????

nastynissan · Feb 25th, 2003, 01:15 PM

Is your truck early 86 or late (newer body style)??? If its older the pump relay should be on the passenger side kickpanel by the heater fan. Its a little black box with a couple other relays around it.

Feb 26th, 2003, 08:17 AM

I found the module, actually two of them (though only one was hooked up), so it looks like this has been an issue before. I didn't have a multi meter, so I couldn't check voltages, but I tried jumpering it as indicated, and the pump still won't run continuously. It only spurts when the key is turned on and spurts again when the key is turned off. I'm going to borrow a meter today and check voltages. If I "hot wire" the pump to the battery, will it run and can I drive the truck for a short distance to get it to a garage.?

RockyB · Feb 26th, 2003, 11:20 AM

Hi, I had the same problem on my uncles 86 early model pickup(720 series). We couldn't find the problem with the relay and had already hotwired the new pump to the battery with a toggle switch in the cab to turn it off and on. Seem to be a wire going either from the relay to the pump or something. We never got it fixed, so if you find whats the problem please post. What we currently did to get the pump to work, we took out the toggle switch and disconnected the lead from pump to the battery and now tapped it in to the fuse for the radio. So, we won't forget to switch the pump off when we get out. I works every time we turn the key the pump turns on.

Feb 26th, 2003, 11:54 AM

When you hotwired the fuel pump, how did it pump? What I mean, was it a steady stream, did it pulse, did it sputter and spurt? The friend that put the pump on, says it's a "pulse pump" and it's not supposed to pump steadily.

RockyB · Feb 26th, 2003, 12:08 PM

Our pump that we had was a steady flow. Do you have the carbed Z24 engine or the tb Z24i engine? I THINK I'm not that sure but the z24i engine had a pulse type pump for the injection system. On the year of the truck we always had a problem getting parts for it because the autoparts store would asume its a D21 pickup not the 720 pickup. Make sure you have the right pump. Rocky

nastynissan · Feb 27th, 2003, 09:37 PM

You should have a steady flow. If you do straight wire it try to go to a main Ign. circuit, and definitely use an inline fuse. If your flow is still sputtering...the pumps as good as DEAD. For a cheap replacement look for Universal fuel pumps. They are regularly used on Volkswagons and other carbed vehichles. Had one on a Ford 300 straight 6 and never had a problem.

Hold On.....If its a Tbi the Universal Pump wont work. Sorry

nissannut · Aug 14th, 2003, 11:32 AM

86 720s have a frame mounted pump. 86.5 d21 hardbodys have the fuel pump in the tank, unless you have a rare 86 z24i fuel injected 720.

The ECU turns the pump on when the key is on for a few seconds to build up pressure.

The fuel pump control relay ONLY turns off the fuel pump when there is no OIL pressure.

The fuel pump control relay do go bad. Sounds like a cheap bad fuel pump. Did you check the second fuel filter? the one in the fuel pump???

jerris · Sep 19th, 2003, 11:52 AM

Rocky B stated this:
"What we currently did to get the pump to work, we took out the toggle switch and disconnected the lead from pump to the battery and now tapped it in to the fuse for the radio. So, we won't forget to switch the pump off when we get out. I works every time we turn the key the pump turns on."
This is what I need to do until I can find permanent fix. How do I tap into radio fuse. Do I just run the wire right into the socket, or do I need some kind of an adapter. I'm horrible with electronics so if you could break it down like I were 5 years old that would be great.
One last thing; which exit out of the cab did you use to run the wire back to the fuel pump.

RockyB · Sep 19th, 2003, 07:16 PM

DISCLAIMER: What I give here is advice. What you do, I'm not responsiable for the outcome. A experienced person who has a understanding of electrical and mechanical should perform any major work, if you can't do the job. Just be safe when working with electrical near gas fumes. RockyB

Hey jerris,
For your hardbody truck, first do you have a haynes or chilton's repair manual for your vehicle? If you do great if not go get one, this will come in really handy. In the repair manual find the wiring diagram for the ignition and fuel pump system. Basically on the 720 series truck I had, I ran a seperate wire from the external pump to the cab, then we found the wire for the radio that only gets power when the key is in the start and run position. We then spliced the seperate wire from the pump to this wire. The radio wire that had power when in the run and start position already had a inline fuse, so we didn't have to worry about that. In your case, look at the repair manual and see what wire leads from the ignition switch to the pump to supply the pump power. Get a test light at a autoparts store for cheap if you don't have one and test the power line to the pump at the ignition switch when the key is at the on/run position. If the test-light lights up well you know that the falt is not there. The next thing to check is the fuel pump relay. I really don't have good luck checking these things, so, what I do the check it is to pull a good known relay out and switch it with the fuel pump relay. Try to then start the truck and listen for the fuel pump to activate(you should hear a humming from the gas tank). If nothing happens then you might picked a bad relay or the wires to the relay might be no good.

For the quick get you going aproach: go underneath the truck and find the wires from the pump going to the front. One wire should be ground and the other is the power wire. Go to the autoparts store and buy some electrical wire for a positive lead. Leave enough of the positive wire from the pump and cut it. The original power wire securely tape it and keep it away from any moving parts. The wire that goes to the pump attach the new wire to it and securely run that to the cab. Now basically you would be doing what I did with the 720 I had. Find the wire from the radio that gets power when in the run and start position and tap that new wire into that wire.(check the manual for the wire) When you try to start it listen to hear the pump activate.

I hope this helps you.
Rocky