New member, been following and getting advice for years here, just never have posted or registered until now. I normally like to use search, but could not find what I was looking for.

I recently acquired a 1989 F250 with the 5.8, I bought it not running. The kid I work with that sold it to me, it broke down on him driving down the road. It will run on ether, so I know it has to be a fuel issue. He had told me the front tank had not worked since he had it.

I done a few diagnostics last night, and this is what I came up with. Seems to me that everything checks out with the relay, computer is activating the fuel pump. When I jump pin 2 and 6 on the self test, the inline high pressure pump comes on and stays on, but the tank pumps do not. I am 99% sure that the tank pumps are shot, but is there a way I can check to make sure I am getting power back to them before I replace the pumps? I figured I could use a test light and check, but really wasnt sure if I might burn up a fusable link if I grounded out the power going in to the pump to check.

I took off the bed last night to make it easier to get to the fuel pumps, way easier for me to do that.

The front tank is completely full of what use to be gas. My guess it went out years ago, and previous owners never fixed it, and then the rear finally went out.

 

No need to fear about using a test lamp to verify power is getting to the in tank pumps. I highly suggest using a test lamp and not a high impedance DVM when troubleshooting the fuel pump circuit. If you find no power then step back and test the tank select switch.

 

@rla2005 thanks a bunch! I just wanted to make sure I was on the right track. Jump pins 2 & 6, and check the tank pumps for power should be correct. Do you think it would be a good idea to unhook power to the high pressure inline pump while I am doing it, to keep it from running dry?

 

Correct, keep the jumper on pins 2 & 6 then turn the key to the Run position.

Unplugging the high pressure pump is not a bad idea.

 

@rla2005 jumping pins 2 and 6 didn't work. Never got any juice to the pumps. However I did pull the fuel pump relay, jump wires 3 and 4 which energizes the circuit. I did have power to the pumps. But that isn't supposed to energize until the key is on I'm pretty sure.

So with the 2 and 6 not working, but the relay plug 3 and 4 working....does that lean toward a bad relay or a bad ground in the computer?

 

When you jumpered Pins 2 & 6 before the high pressure pump turned on. The high pressure and in-tank pumps use the same power source/relay contact. Refer to the diagram above.

 

@rla2005 I mistyped that. I had jumped the 3 and 4 on the relay plug and got the high pressure to come on, without turning the key on. Tonight I tried the 2 and 6 and got nothing. I just tried grounding the 6 and got nothing.

 

@rla2005 I found a post where you told someone to check inertia switch if 2 and 6 didn't work. I'll check that tomorrow after work. Thanks for the help

 

If you cannot get the fuel pump relay to energize by jumpering Pins 2 & 6 or jumpering Pin 6 to ground that does point to a bad relay or bad connection. Since you do have power to the high pressure pump when you jumpered the contacts on the relay socket that does indicate the inertia switch is good.

 

@rla2005 thanks...I was thinking that possibly. I'll stop on the way home and buy a new relay for it and if that don't fix it, I start looking for a bad connection after I get back from a work trip here in the next couple weeks. I really appreciate the help. It was a good feeling to have the truck running last night when i jumped the fuel pump relay plug, truck actually sounds really good. I do know now that the front fuel pump is bad, have power to it, but no go. Rear pump is good. The tank selector switch is working. All good things.

 

The relay sockets on these older trucks are known to grow green corrosion on the bottom side. Take a good look there as well.

 

@rla2005 sorry it took me a bit to reply, down in TX now for a work trip.

But anyway, put a new relay in it and she runs good now. I didnt have much time to check for corrosion, but will next week when I get home.

I know the front fuel pump is bad. I just went ahead and ordered both since I have the bed off, go ahead and replace.

Thanks for your help!

 

Thanks for the update.