OK, I have a problem with my gas gauge.

This problem occurs regardless of which tank I am using, front or rear.

When the fuel level in the tank I am using drops below about 1/4 tank, the gauge works ok. If I have more than 1/4 tank of fuel, it reads more than full. It pegs all the way over on the full side.

Since it does this with both tanks, I thought it might be a problem with the gauge itself. Does that sound right? Or have both of my sending units failed in the exact same way?

Any info would be greatly appreciated.

 

What year is your truck and it's possible both units probly need replacing it will depend on where you live but prices for the sending/pumps units will vary. I paid only a lil over $100 from Parts America for the front tank but the back tank cost me $174 cause i didn't have the cash so i charged it locally.

 

oh man i got me the exact same problem, put in like 9 galllons and it says its full, would it be better to take it to ford dealership or will it cost to much, live right down the street from one

 

It could be either.

Ford uses 75 ohm fuel senders. So a full tank would be 70-75 ohms, empty would be 0-2 ohms.

Now there are two problems with this.

First, many aftermarket replacement senders use the same element, in different housings, thus saving manufacturing costs. Many of them use a 90 ohm element. So if your tank's have aftermarket senders, "full" will be "way past" the full mark.

Also, because the more resistance there is, the higher on the scale the needle goes, the aging of the wires, poor grounds and so forth, add to the resistance. The fuel sender is grounded at the tank - so the stuff between that ground, and the ground on the firewall for the cluster, is a lot of potentially rusty stuff. The tank hole plate it mounts to, the tank itself, the tank straps, the frame, and the body bolts/ground strap under the hood.

It's not uncommon for the fuel gauges to drift as the vehicle ages. To test this, run one of your tanks to "E", essentially empty, but not empty enough to stall the engine and plug the fuel filter. Then disconnect the battery, pull the cluster, and measure the resistance between a good ground on the firewall, and the wire in the connector that's for the fuel gauge. Flip the tank switch to each tank, one should have a very small resistance depending how empty the tank is, and the other should be 70-75 ohms if it's completely full.

If you do have "correct" readings on your ohm meter (testing at the cluster connector), then it's the gauge itself (unlikely).

If you have incorrect readings at the cluster connector, you can drop one of the tanks and measure at the fuel tank itself. If it's correct there, then you know it's ground related. If it's incorrect at the tank, then you know it's the sender itself.

This is why garages will charge some money for this... measuring it at the tank is difficult because most people have hands that don't fit between the bottom of the bed and the top of the tanks to disconnect and reconnect the connector. I was able to do this on my side tank, but not the rear tank. My hands are "medium" I guess !?

I had the bed of my truck off for part of the summer doing body work so I decided "screw it" and replaced both pumps and senders, so I don't have to think about failure in either tank for years to come. I hate spending money that I don't need to, but I hate taking out gas tanks even more.

 

Ok iam new to this all so bare wit me.
You talked about 2 tanks, i got me an f-150 87 1 tank how would i go about applying your instructions to mine.

 

Hey thanks Frederic.I should have thought of that, but it has been nearly two decades since I had fuel gauge problems on a vehicle. Also this is my first dual tank vehicle. I will check that out this weekend when the guy who traded me the truck brings it back from his buddies shop (getting a nice new steering box installed).

If the senders are bad I will try getting a few from the local trucks only junkyard for a few bucks each, before I drop all that cash on new ones.

It seems to me that I have a universal sender around here somewhere that came with my Dakota Digital Gauge set for another car. Maybe I will try that as well. Does not cost anything to test it!

 

Spike - the process is the same for single tanks, except ignore the parts where I say "flip the tank selection switch", as there is none.

Shrug - no problem. I went through this (more or less) when I was grafting in a t-bird digital cluster into my truck.

 

By the way, on my 87 F-150, what size would those tanks be?

 

The rear is likely to be a 17 or 18, and the front is likely to be a 17 or 19.

Don't you have a gas bill? ::smile::

 

Well I have only had the truck since Monday. I drove it one day before finding out the steering box was shot, then the guy who traded me took it to have it repaired. It will be back tomorrow.

I shudder to think what it will cost to fill it up at $2.48 a gallon!

I can only imagine it will cause me more heartbreak by getting about 6 mpg!

I like my Taurus. 19mpg. I know there are more economical cars, but I am to big to wedge my butt in to a Hyundai. The Taurus is just the right size for me.

Thankfully most days my wife and I will be sharing the car. She only works about two miles from my school. (School! At my age! AACCCKK!)

 

My 87 f150 is a 21 gallon tank if that helps in any way lol

 

19 in a taurus? You must have a lead foot, or something is wrong. my '99 Crown Vic, which is much bigger, heavier, and has a bigger engine, gets 28-29 on the highway if my foot isn't buried on the throttle. My 93 Continental, which is very taurus-like, actually hits 30 mpg on the highway consistantly.

Your truck should do better than 6. My old tired crewcab gets 12-15 depending on how I drive.

 

Part of the problem is that my wifes commute to work is about 21 miles each way, and because the freeway gets so jammed up every day she has to drive entirely surface streets. The car almost never sees the highway. Plus she hates to have the windows open at any time so the A/C is always on.
We did make one drive from Phoenix to Los Angeles and got about 28 mpg then.
Traffic is a bit*h! I miss my old 53 Chevy with the 235 straight six. 21mpg city!

So you really think that big ol extended cab truck with the 351 w/edelbrock carb will do that well? I will be shocked to see it.

 

Gotcha, awful commute. Will do it every time.

Others have had better and worse results than me... with their trucks... but I cannot complain about my mileage, considering it's an F350, and a crewcab, and weighs in at 6997 lbs.