Ford F53 fuel pump

[snerfj]

Purchased a '94 Bounder 34 in May, hit the road in June, and had the classic fuel pump / hot weather issue. I just replaced the pump with the new Ford part, connected the pigtail to the harness and plugged it in. My question is, when the ignition key is turned to the On position (not Start), should I hear the fuel pump running in the tank? I'm underneath, wife turned key on, but I don't hear anything. I don't want to raise the tank up and bolt it in place until I know everything is going to work.

Thanks
Jim in NH

[Bassmanks]

Would you share the part numbers and make for the pump and harness thanks.

[theoldwizard1]

snerfj wrote:
It's impossible to get my meter probe into the plastic connector plug end of the pigtail, ...

This is actually a case where an old fashion incandescent 12V test light is better than a meter ! The incandescent bulb will require about 1/4A to light. An inexpensive way to "back probe" most electrical connector is to use a heavy T pin (like from a bulletin board) and an alligator clip. The pin is stiff, but thin enough that you can insert it from the back side of the connector.

The test light won't read voltage, but you will quickly know if it is adequate by how bright the light is. Some mechanics actually make their own test lights using 2 bulbs so that they know that the circuit is capable of 1-2A.

[Dutch_12078]

Ahh, ok, I was just curious if there was any difference in the reading. As far as I can tell from digging through the wiring diagrams, the pump should be running on the full 12 volts. I see nothing between the inertia switch and the fuel pump except a long wire run.

[snerfj]

When I was checking voltage at the pump, it was on the bare pink wire coming out of the main harness, before I connected the pigtail. That was after removing the pigtail that I had connected with Posi-lock connectors. It's impossible to get my meter probe into the plastic connector plug end of the pigtail, it's a very small opening so I don't know what the voltage is now. I've looked before but couldn't find any electrical specs for the PFS-48 fuel pump. I'll try again, maybe reach out to Ford / Motorcraft.

[Dutch_12078]

Did you recheck the voltage at the pump end after redoing the connections? You might have inadvertently crimped partially on the insulation the first time around, resulting in a high resistance connection dropping the voltage. Or there might have been some anti-corrosion coating on the plug or pump terminals causing a voltage drop that cleared up with additional insertions.

[snerfj]

Well, on a lark, I figured that if nothing is making sense, it can't hurt to hook it up and see what happens. So I crimped on new connectors to the pigtail, plugged them in, raised the tank up, and had my wife turn the key on. The fuel pump came on! Turned key off and on again, same thing. So I crawled out from under the tank and had her start the motor. OMG it started right up!!
Dropped the tank once more to put heat shrink on the connections and tape everything up. Lifted the tank again and it still starts up, so I think I'm done. Tomorrow I'll finish bolting the tank in and give it a test drive.

Thanks for all the help. Still not sure how it can run on 7.85 volts but maybe that's all the pump needs.

Jim in NH

[snerfj]

Probed the fuel pump relay terminals: 12.55v across terminals 30 (+) and 85 (-) with ignition off. Ignition on, that connection reads 0 volts, but terminal 30 to a frame ground still shows 12.55 with ignition on. So something is apparently happening on the ground side of that relay.
Jim

[snerfj]

Thank you, Dutch. I did see that thing but thought there are too many wires coming out to be a simple switch. I'll try and probe it for voltage.

Jim

[Dutch_12078]

snerfj wrote:
I was just out there, standing on my head to get under the dash. I don't see anything that looks like an inertia switch with a button. Then I looked under the rv where the steering column comes outside, nothing there either.

Here's a photo of one:


Click For Full-Size Image.

[snerfj]

My relay plan isn't going to work, 6 volts isn't enough to trigger a 12 volt relay. So I'm going to have to trace the circuit from the front to see where the voltage drop is. Now I wonder how the old pump ran on 6.85 volts. Or maybe that was the actual problem. Although it ran fine except when the outside temp got up to 95.

Jim

[snerfj]

I was just out there, standing on my head to get under the dash. I don't see anything that looks like an inertia switch with a button. Then I looked under the rv where the steering column comes outside, nothing there either.

[Dutch_12078]

Try checking the voltage on both sides of the inertia switch. The switch is directly in series with the pump.

[snerfj]

Swapped the horn and fuel pump relays, still showing 6.85 volts back at the tank. Rather than spend a lot of time finding the fault in the harness, I think I'll just run a new line from the battery to a relay back at the tank, and have the 6.8 volt line trigger that relay so the pump will get a full 12 volts. The yellow wire for the fuel gauge is also showing 6.8 volts.

[dr3x]

I should look before speaking just to lazy to. My question would be does it have 2 pumps 1 tank mounted the other frame mounted. Also agree 6.85 won't get it for pump.