Fuel Gauge pegged - where to start looking

[Sparks-IDI]

Wanted to update and ask some additional questions. So for me since I have a fork truck it was a no brainer to take the bed off rather than crawl around under the truck, Pic 01.

I could not belief the condition of the sending units. Check out the corrosion. Pic 02. I noticed that there is no filter screen on either unit. Should there be one? I would think Ford would have something there. I know the bed has been off before as there were only 4 bolts holding it down. Maybe previous owner pulled them off?

I checked on new sending units there like close to $180 and I need two. So I figure maybe I can repair them since really they are pretty simple. What have I got to lose.

Biggest problem was the wiper grounding point. So I sand blast and silver solder that point. After I cleaned everything up and reassembled it worked. Except the wiper board had a dead spot about the 3/4 tank full spot and the resistance goes way high. Tried cleaning it with a pencil eraser but no dice. See Pics 03,04,05,06.

So at that point I say forget it and started searching on line and found some on eBay for around $100 each.

TRex Auto Parts https://www.ebay.com/str/trexautoparts?_trksid=p2047675.m3561.l2563

That screened funnel, on their website, is that what I need or could use?

Thank you to franklin2 who posted the schematic above. It really helps. Although I think it must be for pre 1994 trucks because the wiring color codes seem different for what I have. You would think the black wire at the unit would be ground as shown in the schematic. In fact, when I was checking continuity on the unit I have, it is the grey/red stripe wire that grounds to the sender?! Is that the correct schematic to fit my truck, a 1994 VIN K Turbo truck? It does not seem to completely represent what I have. I think '94 Ford changed things. If anyone can corroborate any of this I would appreciate it. Pic 07,08

Finally, Pic 09. What is this? I assume it is a type of pressure relief valve. I assume there is nothing I should do with it, or should I take a chance and pull it out and check for operation? I don't want to pull stuff apart and risk breaking something unless I need to.

 

[Sparks-IDI]

The other Pictures. There is a limit of 5 pictures per post. Now I know.

 

[quickster]

That hose is just a vent. Take a look in the tank and see how much mud you have. Without the shower head on the end of the pickup tube you will run out of fuel at 1/4 tank. Well when I put the new sender w/ shower head I pulled so much crap out of the tank I clogged 3 filters to the point that the truck would stall. I ended up getting new tanks.

 

[Old Goat]

Check out this site, they also have what you need.

Ford Pickup Diesel Sending Units

Do the job right the first time with the right Fuel Tank Sending Unit, at the best price. Shop our best selection of correct fitting Ford Diesel Fuel Tank Sending Units for your Ford Diesel F250 or F350 from Gas Tank Depot.

www.gastankdepot.com

Now you have the bed off, good time to up grade to the 38 Gal rear tank.

That was my truck, I would deep 6 all that worn out rusty junk.


Goat

 

[12pilgrim]

I can't believe how rusty those senders are. Dang! I bought new senders from Trex and they have been good.. although my rear tank has stopped reading on the gauge after a year. I'm guessing a bad ground/connection

 

[Old Goat]

I agree, those are really rusted units. When I replaced mine along with the 38 gal rear tank, the top were rusted prety good, but the parts inside were in good shape. Iam amazed at how rusty the senders are in the pictures.

When I installed my new Senders, I coated the tops with Anti-Seiz thinking it would protect them. I put them in about 3+ years ago.

My Shower Heads were broken off, but no mud, dirt or other debris in the tanks.
Lot of guys want to eliminate the Shower Head`s but they are your first line of defense with the screen on the suction end to keep anything getting into the fuel Switch Valve.

When I bought the 86, it was 28 years old, have no clue if original or been replaced some time in it`s life.
So how many years they last, have no clue, so when Iam 104 years old, I`ll pull the bed to check them and let you know... that should be another 28 years from when I replaced them...

Goat

 

[typ4]

The gauge pins to full if there is an OPEN circuit, not a ground.

 

[Clb]

Bump

 

[Sparks-IDI]

Guys, I wanted to give a final update on my fuel tank issues. I bought this truck I think pretty cheap at $1800. The thing is, it is solid. No rust at all except surface rust on frame. Body absolutely solid. Only problem is someone did a Saturday night, a case of beer and 3 guys paint job on it. But I am overlooking that as it is a solid truck. So systematically going thru it and repairing things. So I pulled the bed and you can see above what a mess the fuel system was. I pulled the tanks cleaned the front plastic tank, replaced the rear steel tank (about $85 at Rock Auto) and new sending units. Also replaced the tank selector valve. While all was apart I wire cupped the frame as best I could, de-greased it and used stuff called Rust Kutter I got from Tractor Supply, to help subdue the surface rust on the frame. That actually worked pretty good. Then a nice heavy coat of satin black Rustoleum with a spray gun. Could not really paint inside of the frame rails so I used some stuff called Fluid Film with carbon black in it. Sprayed the stew out of it everywhere I could not get the paint gun to. It worked out really well I thought. Fluid Film is like cosmoline.
Ok here is the kicker/warning. I thought I was home free as I had replaced really everything in the fuel system. So I turn on the ignition and I blow a fuse #6 to be exact in the dash. Ok, so I replace and try again. Flip the fuel switch and blows another fuse, #6. So I spent 2 or 3 days off and on trying to troubleshoot my wiring connections, etc. So is the China fuel sector valve the problem? I don't know. Needless to say I was frustrated. Now I had bought several months back a new fuel rocker switch as the old one was messed up from someone trying to glue it back into the dash. I bought this one on amazon.

https://www.amazon.com/WFLNHB-Replacement-1992-1997-F2TZ-9A050-B-F2TZ9A050B/dp/B08HHB8FNR/ref=sr_1_3?crid=1V42SKKJYNPCR&keywords=1994+ford+truck+diesel+tank+switch&qid=1677165173&sprefix=1994+ford+truck+diesel+tank+switch%2Caps%2C137&sr=8-3#customerReviews

The description is right, I have a 1994 F250 Diesel, so I bought it. So while trying to figure out the issue, I just for grins dug thru the pile of old parts and retrieved the old switch. I over the years, when working on anything do not throw anything away until I am completely done. How often do you wish you had the old part to see how it was put together or to compare to what you are trying to install.

I plug it in and WTH.. it now works! OK, so now I know the new switch is apparently bad. I decided to see if I could pry it apart without breaking it. I see the contact slider that moves and the contacts on the new switch. I then open the old original switch and the contact slider is completely different!? And upon careful inspection, I could see an arcing point where the short was occurring in the new switch. Fortunately, the plastic switch bodies are the same so I just moved the old contact slider into the new switch body. Now all is good, gauge works.
I just wanted to let others be aware that a so called new switch might not be for your application. If you read the amazon switch description, it says it covers 92-97 diesel. If you check some of the reviews for the switch there have been others who had the same problem of blowing fuse #6. Is it possible there were different switches for diesels during the years 92-97? NA vs Turbo? My truck is a VIN K truck and originally had a turbo motor. But somewhere in history the motor was changed out and now is NA.
I think I can now put the fuel issue to rest.. finally. Also, don't throw anything away until you are completely done. I am glad I had the old switch.

PS The Pic 12 bolt mod is my modification for a bed hold down bolt. The original had an oval shank to prevent it from spinning when tightening or loosening. I really could not find them online so I just went to HD and bought 3.5 and 4.0 inch long 1/2-13 carriage bolts and made my own. The flat sided piece is TIG welded to the underside of the bolt head.

 

[Sparks-IDI]

Rest of Pictures

 

[Clb]

Stickies, grounded wire,sender

Fwiw my kid used to lift 1 side of the bed up @ the stealership to access senders, pegged f sounds like a short to groung, as an open circuit reads m t

Sounds like I got this backwards...
Trust but verify

 

[franklin2]

There is no hard and fast rule on the gauge sweeping to full or going empty. The 1986 and down trucks work opposite of the 1987-up truck sending units. Those diagrams I posted earlier in this thread are 1986-down diagrams. Here is a 1992 diagram, which should represent the 1987-1993 wiring. I can't find a diagram for the 1994-up trucks.