Help!
Thread Starter
|
New User
Joined: Dec 2016
Posts: 6
Likes: 0
Help!
I have got a 81' Ford F-150 300 6 and my gas guage will bounce around a couple times a week, Last week it said I had 1/2 a tank, then to 1/4 of a tank, now without putting any gas in it, it says I have 3/4 of a tank, can someone tell me what is going on here because I am stumped
Thanks!
Colin
Thanks!
Colin
Lead Driver
Joined: Jul 2009
Posts: 6,477
Likes: 19
From: Sheffield, AL
Welcome to the forum, Colin Seaberg!
Likely, it is the in-tank sending unit. There is a single wire which connects to the sender and is attached at the top of the fuel tank. If you can loosen the wire and touch it to the frame [electrical ground] with the key in the "on" position, the needle should swing all the way to full. If it does, that indicates that the gauge and associated wiring is okay. That would point to the sending unit being defective.
Likely, it is the in-tank sending unit. There is a single wire which connects to the sender and is attached at the top of the fuel tank. If you can loosen the wire and touch it to the frame [electrical ground] with the key in the "on" position, the needle should swing all the way to full. If it does, that indicates that the gauge and associated wiring is okay. That would point to the sending unit being defective.
FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
Yes, welcome to FTE!
Don't forget the Instrument Cluster Voltage Regulator. It serves the fuel, water temp, and oil pressure gauges, so if it is going bad all three will bounce around. Are they?
Don't forget the Instrument Cluster Voltage Regulator. It serves the fuel, water temp, and oil pressure gauges, so if it is going bad all three will bounce around. Are they?
FTE Legend
Joined: Nov 2015
Posts: 30,831
Likes: 4,096
From: Angier, NC
Then I would say it is the sending unit.
I don't think the float fell off as it would not move the gauge at all so I think it is the sweep arm to the wire the issue.
You did not say what size tank or where this tank is located but know when you go to replace it if it is the side 16 gal tank, the size for a short bed, some places list the same sender for the 16 gal and the 19 gal (long bed) and this is wrong, 2 different senders.
Also IIRC the 19 gal side tank and the 19 gal rear tank (long bed duel tanks) use 2 different senders between them.
I think I got my 16 gal (short bed side tank) from AAA.com on line but would need to check that to make sure.
Dave ----
I don't think the float fell off as it would not move the gauge at all so I think it is the sweep arm to the wire the issue.
You did not say what size tank or where this tank is located but know when you go to replace it if it is the side 16 gal tank, the size for a short bed, some places list the same sender for the 16 gal and the 19 gal (long bed) and this is wrong, 2 different senders.
Also IIRC the 19 gal side tank and the 19 gal rear tank (long bed duel tanks) use 2 different senders between them.
I think I got my 16 gal (short bed side tank) from AAA.com on line but would need to check that to make sure.
Dave ----
Thread Starter
|
New User
Joined: Dec 2016
Posts: 6
Likes: 0
Thanks for the help!
It is a long bed and 2 tanks, the front tank when switched does not show how much gas is in it but when I flip it to the rear it shows but like I mentioned before bounces around, it stays at half a tank now, on saturday I will fill her up completely and see how she reacts.
Posting Guru
Joined: Jul 2015
Posts: 2,239
Likes: 5
From: Northeast Ohio USA
My rear tank sending unit is shot and shows "E" when switched but supplies fuel. The midship tank's sender works fine. I calculate how many miles i get out of the midship tank and apply it to the rear tank. Regardless, i fill both of them when it's time for a fill-up. How many miles do you average per tank of fuel ?
Trending Topics
Posting Guru
Joined: Jul 2015
Posts: 2,239
Likes: 5
From: Northeast Ohio USA
Excuse my lack of manners
Welcome to FTE and the Bullnose forum ! Blue Ox is more sensitive and she reminded me of my short coming.
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
2027 Super Duty Carhartt Package First Look: 12 Things You NEED to Know!
Michael S. Palmer
10 Most Surprising 2026 Ford Truck Features!
Joe Kucinski
Top 10 Ford Trucks Coming to Mecum Indy 2026
Brett Foote
5 Best / 5 Worst Ford Truck Wheels of All Time
Joe Kucinski
Ford Super Duty: 5 Things Owners LOVE, 5 Things They LOATHE!
Joe Kucinski
Every 2026 Ford Truck Engine RANKED from WORST to FIRST!
Michael S. Palmer
The Best F-150 Deal of Every Trim Level (XL through Raptor)
Joe Kucinski
FTE Legend
Joined: Nov 2015
Posts: 30,831
Likes: 4,096
From: Angier, NC
It is a long bed and 2 tanks, the front tank when switched does not show how much gas is in it but when I flip it to the rear it shows but like I mentioned before bounces around, it stays at half a tank now, on saturday I will fill her up completely and see how she reacts.
Now we figured that rear tank sender is on it's way out the way it is bouncing all over the place.
Now for that front tank, does it supply fuel but just does not read or not fuel & no read?
Switch to the rear tank and take the wires off the sender.
If it is like mine and I think others as well, 1 wire is a ground and the other the gauge wire.
With a test light you can check each wire at the plug, gauge wire should blink the light the other no blink.
If you use that no blink wire as a ground to test the blink wire you will know each wire is good.
If no blink or ground you will need to trace back the wires to see were the issue is and fix it.
To check the gauge use a jumper from blink wire to ground. The gauge should go to full.
If the above checks out good then the side tank sender is bad also.
Now for no blink and tracing so trucks IIRC the gauge goes thru the fuel switch valve, others the dash switch.
I would also think if the gauge is bad you may not get the blinking but you do have the other tanks the reads ok sometimes so I am thinking it is either a bad switch/valve or sender.
good luck
Dave ----
Thread Starter
|
New User
Joined: Dec 2016
Posts: 6
Likes: 0
Yes it still sends gas, just does not read how much it is in the front, and the front tank has a huge dent and is a 10 gallon tank, the back reads 20 (weird I know, but the guy I bought it from was trying to make it a "Race truck")
FTE Legend
Joined: Nov 2015
Posts: 30,831
Likes: 4,096
From: Angier, NC
Does the dent make the side tank a 10 gal?
I ask because a stock long bedside tank should be 19 gal, the short bed 16 gal.
You can not put a 19 gel tank in place of a 16 gal as I tried and would not fit.
On the rear I guess if bone dry you could get 20 gal and that is close to the stock 19 gal as not to worry.
On the side tank if you can get to the wires pull them off and test like I posted and see if the gauge works when grounded.
Dave ----
I ask because a stock long bedside tank should be 19 gal, the short bed 16 gal.
You can not put a 19 gel tank in place of a 16 gal as I tried and would not fit.
On the rear I guess if bone dry you could get 20 gal and that is close to the stock 19 gal as not to worry.
On the side tank if you can get to the wires pull them off and test like I posted and see if the gauge works when grounded.
Dave ----
Posting Guru
Joined: Jul 2015
Posts: 2,239
Likes: 5
From: Northeast Ohio USA
They should have been approx. 19 gal. each with a slight reserve. If the original midship tank is only holding 10 gal, that must be one heck of a dent 
(more like a brutal beating with a 5 lb. sledge). Have you peeked up under the truck to see if maybe the tank was swapped out ? (for what I don't know). If it was beaten into 10 gal. submission, I'd be concerned with it's original mounting situation. I'd also be concerned that the dents might me occluding the sender arm or float itself causing it not to move. Any pics ?
Thread Starter
|
New User
Joined: Dec 2016
Posts: 6
Likes: 0
I will try to get some soon, after I am done with my work, all I know is that it looks like this truck was trying to go over some rocks and maybe the truck went up and landed on a rock is what it looks like.
Thread
Thread Starter
Forum
Replies
Last Post
dylan1952
1948 - 1956 F1, F100 & Larger F-Series Trucks
2
Feb 6, 2007 11:18 PM