Fuel Pump doesn't run | Ford Explorer Forums - Serious Explorations

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Fuel Pump doesn't run

86bandit

Member
Joined
August 8, 2011
Messages
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City, State
Greer SC
Year, Model & Trim Level
1993 Explorer
Just started working on an old project truck with the intention of making it my DD. Its a 1993 Explorer XLT four door.

Currently it does not crank and has no fuel pressure. At some point the factory fuel pump relay has been bypassed to an external relay that is wired as follows;
Pin 30: grounded to the fender
Pin 86: green/yellow wire from the distribution block
Pin 87: Tied in to the black/yellow and pink/white wires under the distribution block
Pin 85: Tied into 2 red wires from the WOT and EEC relays

Does this sound anything like right?

Troubleshooting shows that at the fuel pump connector at the tank (Key On);
Pink/Black wire 10.5 V
Yellow/Black wire 7.2 V
Black Wire: less than .5 ohms to ground

And also the CEL illuminates when you key the truck up.

Any help is appreciated.
 



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with the engine light on the first thing i would do is pull any codes, it may or may not be related. second, run 12v from the battery directly to the pump and verify it works. then you should know if the problem lies elsewhere.
 






with the engine light on the first thing i would do is pull any codes, it may or may not be related. second, run 12v from the battery directly to the pump and verify it works. then you should know if the problem lies elsewhere.

I'll try the straight wiring tomorrow and see what happens. Just to clarify which wires at the tank are pump and which are sending unit? As far as the CEL I only mentioned it to indicate that I probably don't have EEC power relay issues. But thanks for the reply.
 






86Bandit, just throwing thoughts out I wonder if the no-crank is the reason you don't have fuel pressure. In other words, assuming for the moment that it ran with the external relay perhaps something is keeping the computer from allowing the start cycle to begin. I agree with finding out if the fuel pump is working at all, but suspect the problem is elsewhere.
I'm assuming that when you say 'no crank' you mean it turns over but won't start. Or does it not turn over at all (no relay click, no action at all)?
 






If by chance this is a manual transmission truck, it could be the clutch defeat switch on the clutch pedal. They can screw up, and if they don't complete the circuit, the fuel pump and the starter won't get power...
 






wiring for pump should be a thicker gauge than the sender, pk/bk from fuel cut off switch and ground is bk for the pump. that's on my 92, your 93 may be different. if you turn the key and the dash lights come on, you should also hear the fuel pump run for 1-2 seconds.
 






Well good news/bad news.
Good;
Straight wired the original pump but it would not run, so apparently it was bad.

Bad;
Put a new one in and although it runs straight wired it will not run plugged into the truck. So I guess I'll have to start looking into the wiring.
 






With fuel pressure, does the engine try to start? I'm assuming it cranks over but nothing else.
 






Was the fuel pump shut off (inertia) switch also bypassed?
 






The engine turns over but does not crank, that is correct.

And the inertia switch is in place and not tripped. Apparently only the relay was moved from the distribution block to an external location.

Considering the possibility of a flaky ground and the need for just ground the new pump to the frame or other suitable location.
 






Something seems odd to me. I don't remember the color coding, but if I remember right, there are only 4 wires to the fuel tank. Fuel pump power, fuel pump ground, sending unit signal, and sending unit return. I'm guessing the black is the fuel pump ground, While half an ohm is not that bad, it could be enough to drop voltage below working levels depending on how many amps a fuel pump draws. Also, one of those voltage readings is for the pump, and one for the sender. Both are very low indicating a bad ground.
 






Something seems odd to me. I don't remember the color coding, but if I remember right, there are only 4 wires to the fuel tank. Fuel pump power, fuel pump ground, sending unit signal, and sending unit return. I'm guessing the black is the fuel pump ground, While half an ohm is not that bad, it could be enough to drop voltage below working levels depending on how many amps a fuel pump draws. Also, one of those voltage readings is for the pump, and one for the sender. Both are very low indicating a bad ground.

This was my thinking as well. The half ohm could be connection related to the probes or maybe meter offset. Unless someone has other option(s) I think Ill slide the tank back under the truck, plug the pump in an run an alternate ground and see if the pump runs then.
 






Have you swapped out the fuel pump relay with a known good one? 10.5 Volts on a DMM with an open circuit (i.e. no fuel pump connected) sounds a bit low unless your battery voltage is below par. You should see just about the same voltage (ignition on) at the connector as your battery terminal voltage. The 0.5 ohm approximate resistance to ground at the black wire doesn't concern me as much as the 10.5V no load on the pink/black.
 






Still haven't fixed the problem but its only a matter of time so no worries there.

But if anyone has a diagram/photo of the proper installation for the straps I would appreciate it.
 






...But if anyone has a diagram/photo of the proper installation for the straps I would appreciate it.

The front strap goes on TOP of the tank (and mounts to the skid plate) while the rear strap goes under the tank.
 












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