Hello all.

I've done quite a bit of searching and reading of threads, but haven't found exactly what I need.

I recently picked up a '94 F-250 4x4 with the 5.8l ( no tach, fuel and volt gauges on the right ) from a government auction. As I'm going through it, a few issues have come up. The auction notice stated that the rear fuel tank leaks. I spoke with the mechanic that worked on it, and he said both fuel pumps were replaced due to an issue where the truck would just stop running. He believed that the rear tank leak is caused by the seal under the locking ring for the pump / sender assembly not seating correctly, as it only leaks when the tank is 'very full'.

The main issue I have is that the fuel gauge is reading empty for both tanks. I dumped a 5 gallon can of gas into the front tank at the auction lot, and then drove to a gas station, where the front tank only took another 5 or so gallons. After working the pump a bit, fuel was coming up the filler neck, so I had to assume that the tank was full and that the fuel gauge is not working properly. As I intend to work on the rear tank leak issue, I did not add any fuel to that tank. So, the rear tank could very well be empty, but the front should have at least 3/4 or more after the drive home, since it wouldn't take any more fuel.

Today I pulled the tank selector switch, and it tested out fine with an ohm meter. The wires from the sending units to the selector switch connector read 20 ohms for the front, and 7 for the rear. The fuel gauge did go to full when the key was turned on with the selector switch disconnected, so I believe the gauge is good.

I only have a '92 Ford manual on CD, and have compared that with some of the posts I found here, such as a nice wiring diagram someone posted for a '95 fuel system. From what I've read, I'm leaning towards the fuel senders being the issue. I don't think the ohm readings I saw from the sender wires at the selector switch connector are in the proper range. Are the ohm ranges different for a '94 vs a '92? It just doesn't feel right that they both would be bad at the same time.

Are the fuel pump and sender all part of one assembly? I'm only seeing one harness coming off the top of the tanks, and would have expected two if they were separate. How hard is it to pull the bed to get to the tanks? The mechanic said it was much easier than trying to drop the tanks.

From some posts here, and some YT videos, I learned that some Ford vehicles have an anti-slosh module for the fuel gauge, but I can't verify if a '94 does. I'm wondering if that could be an issue. There was also some mention of the sender wiring going through the selector valve, but I think that is only for the diesel vehicles.

My other issue is with the volt gauge. With the key on/engine off, it goes to a mid or so position, which I think is normal. However, once the truck is started, the gauge pegs all the way over at 18. I checked the voltage at the battery, and it is in the expected 14.2 or so range with the engine running. I'm puzzled as to why the gauge would peg when running, but only show a mid reading when not running and the key on.

Lastly, what manuals are best? As I said, I have the CD version from that online auction site for our '92.

Thank you!

 

Bueller? ... Bueller?

Any thoughts, comments, suggestions, links, etc on these issues would be greatly appreciated!

Thanks!

 

Welcome to FTE

Props for having a CD, but there are significant differences from 92 to your 94 so obtaining a specific one should be priority.

Numerous reasons for a 94 to just stop running, but very infrequently the pumps or fuel system are the cause.

Fuel transfer from one tank to the other causing one to overflow is usually #1 with a bullet for "leakage", but the fuel module replacement also usually corrects any sender issues as well since they are a part of a "new" module.

Engine compartment grounds & clean relay sockets are important to proper fuel system operation.

Got nothing for you on the volt meter.

3 things I'd recomend first off is learning how to check codes either manually or with a Inova/ Equis 3145 scanner, reading up on capacitor leakage in the computer & studying up on PIP failure.

Hopefully others will chime in.

Welcome again & good luck.

 

20 ohms on the front sounds like a sunken float in the tank.
7 ohms on the back sounds like a short to ground.

The 1994 and the 1995 are the same:
Attachment 278424

The sender:
Attachment 284348
Attachment 281432

The FDM (Fuel Module):
Attachment 281295

/

 

Thank you for your responses!

Scndsin - I ordered a CD for the '94, so that should help a lot. Check Engine light is not on, so had not thought about pulling codes. Yard mechanic said agency only ran it on the front tank, and so wore out the pump. He changed the rear pump while he was at it, and guesses that there is some issue with the rubber o-ring/gasket for the pump ring causing it to leak when 'very full'.

subford - I think it was a previous post of yours that I copied the '95 wiring diagram from, so thank you for that! I'm sure I'll find it when the manuals arrive, but what is the ohm range supposed to be for the fuel level senders? The rear tank may well be empty, as the truck had been pulled into the government repair yard to fix the fuel leak and was supposed to be run out before the work was done. The agency bought a new truck, so this one was sidelined, and then auctioned.

So a few questions I'd like to get some feedback on:

1) Pull the bed or drop the tanks? ( yard mechanic says the bed bolts are going to spin if I try to take them out, so that adds to the complexity )
2) Best way to drain tanks before dropping them?
3) Does the '94 have the anti-slosh module?
4) Once I get the pump(s) out, I presume I should pull the fuel pump relay so I can have the key on to test the fuel level sender(s) ?
5) If the float(s) are bad, can they be replaced on their own, or does it require a whole new sender?
6) Any suggestions on the odd behavior of the voltage gauge? ( reading ~12v key on/engine off and pegged at 18v with engine running while a DVM shows 14.2 at the battery, needle does drop all the way down when key is off )

Thanks! ( clicking Post before I think of anything else to add... :-) )

 

Fuel Gauge, Resistance
With the sending unit float arm in the empty stop position, resistance should be 15 ohms (below E). With the sending unit float arm in the full stop position, resistance should be 160 ohms (above F). The fuel gauge should read empty at 22.5 ohms and full at 145 ohms. In other words an open circuit will peg the gauge passed full and a short circuit to ground (zero ohms) will peg the gauge passed empty.

I like to pull the bed.You may need to use a thread chaser on the bed bolt threads and spray them with penetrating oil for a few days before removing the nuts. I have also had to weld a nut on the top of the bolt to hold it. But it is better than broken tank straps.
Hand pump.
Only the '94 vans and cutaways. The F-series trucks do not use them.
The pumps will only run for one second each time the key is turned to the run position so need to do that. You only need to pull the relay if you are cranking the engine and not starting it to keep the fuel out of the oil. The fuel pumps will run all the time the engine is cranking or running.
The floats can be replaced. The fuel gauge sender is is separate from the pump (FDM). Both are attached to the fuel hanger and use one pig tail from the hanger to the plug near the frame.
Remove the cluster and check it out on the bench with a variable DC power supply.

 

Concerning the volt gauge, I know that if the cluster was swapped with a different model year, someone could have re-pinned the connectors in back and that could be the problem.

I know this because I swapped a '92 with a '95 cluster and had to re-pin the connectors in back. Everything worked great but the volt gauge showed max when running and I believe half way when off.

And it could just be fluke with the cluster you have.

 

Subford - Thank you for the answers!

Timbersteel - What do you mean by "re-pin"? I'm guessing that means moving wires around in the connectors on the back of the cluster. I wasn't aware that was something that needed to be done when swapping around clusters. After looking at some videos on cluster repairs, I can see that the cluster seems to be broken down into 3 or 4 individual sections, and so wires could need to be moved around to accommodate a different layout. I think this is the original cluster, as I can't see why they would have changed anything around in it, but intend to check voltage readings at the gauge to see if the gauge really is reading 18+ volts with the engine running. My thought is that the gauge must be faulty.

 

Yes, if someone swapped in a different year cluster, then it may have been re-pinned. But that's only for different years, ie. A '94 cluster in a '92.

They have to swapped as follows
92-93/94-95/96-97. Then there is no wiring change.
You can swap '94-95 into '92-93, its just the wiring that needs moved around in the connectors.

 

 

Fly18s - that is an interesting thought. There is an alignment issue between the driver's door and the fender that I might need to have a body shop look at. I'm sure part of it is just worn hinges/pins, but there is paint damage evidence that suggests something happened there. The door is not closing fully, unless shut hard, leaving a good gap between the door and the frame at the top front edge. A daylight size gap. I'll have to see if they can pull the bed for me and store it while I fix the issues with the tanks. They might be able to address any issues with the bed bolt holes while it is there.

Thanks!