broken gas guage??
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Freshman User
Joined: May 2006
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broken gas guage??
ive got a 78 f-350 with a 351m dually 2by 4 ok, just the other day i was driving down the road and the gas guage went to empty really fast form 3/4 of a tank, so i tried to fill er up and i only got 3 gallons in and the guage still wont work, is it the sender unit, and how bad is that to replace? and is it going to kill me financially, any recomendations help alot, thanks
Posting Legend
Joined: Sep 2001
Posts: 30,255
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Sender unit, broken wire/connection... Trace it down.
If you ground the wire very briefly at the tank it should make you gage peg over full. If it does the problem is in the tank. If it does not you have a problem in the wire or gage. Do not leave the wire grounded or you can burn up your gage.
The sender unit can be purchased form the sponsor vendors. The labor to replace it is the tough part.
If you ground the wire very briefly at the tank it should make you gage peg over full. If it does the problem is in the tank. If it does not you have a problem in the wire or gage. Do not leave the wire grounded or you can burn up your gage.
The sender unit can be purchased form the sponsor vendors. The labor to replace it is the tough part.
Freshman User
Joined: Jan 2006
Posts: 45
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From: DFW, Texas
I had the same problem awhile ago. Mine turned out to be the sending unit...the float had sunk. I was able to determine a bad unit vs gauge by detaching the wire from the sending unit and touching a 9v battery to the wire. If the gauge pegs, then you know its the sending unit.I bought a new sending unit from one the the catalog sponsors for under $75, and had a local shop drop the tank and put it in. They just charged me 2 hours of labor. I did not want to mess with a gas tank & fuel vapors in my own garage.
FYI....if it is your sending unit, it's a good time to check the fuel filler tube from the tank to the fuel door. If it's old & brittle, it's a perfect time to replace with the tank being dropped.
FYI....if it is your sending unit, it's a good time to check the fuel filler tube from the tank to the fuel door. If it's old & brittle, it's a perfect time to replace with the tank being dropped.
New User
Joined: Jan 2008
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A guuge that won't read is caused by
1) Fuel in the float ...so it drops to the bottom of the tank and registers empty.
2) a Faulty ICVR (which would also cause the oil pressure gauge to drop to zero as well.
3) a faulty Sending unit that just won't work anymore.
First check for a pulsing 5 volts in the sending unit wire.
If there is current that ICVR is fine.
To check the guage quickly touch the fuel tank signal wire to ground with the key in run, if the gauge pins to the right ....the guage is fine.
If the gauge doesn't move,the wire could be broken and therefore won't make a reading.
1) Fuel in the float ...so it drops to the bottom of the tank and registers empty.
2) a Faulty ICVR (which would also cause the oil pressure gauge to drop to zero as well.
3) a faulty Sending unit that just won't work anymore.
First check for a pulsing 5 volts in the sending unit wire.
If there is current that ICVR is fine.
To check the guage quickly touch the fuel tank signal wire to ground with the key in run, if the gauge pins to the right ....the guage is fine.
If the gauge doesn't move,the wire could be broken and therefore won't make a reading.
Senior User
Joined: Oct 2003
Posts: 418
Likes: 1
From: Nice, California
Olblue77, yeah I'd have someone do that for me too, but 2 hours of labor is too expensive out here in CA ($85 an hour x 2 = $170). My gas gauge didn't used to work when I first got the truck, turned out to be a bad fuel gauge. But usually it's either the float gone bad, or just a bad sending unit.
Dan
Dan
Postmaster
Joined: Apr 2000
Posts: 2,838
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From: SD
I've had to repair several pickups with this trouble - every time has been bad wiring. Look over the wires along the frame rail and near the tank. They get dry and brittle and crack apart. I usually replace the wire along the frame to the sender and the ground wire to the frame. Be sure to solder all splices and sand the grounding point clean and coat with dielectric grease for a good connection. The sending unit requires a certain amount of resistence for the guage to read - poor wiring and bad ground connections change the resistence and throw off the guage. Try this first before you replace the sender or drop the tank.
Marty
Marty
Senior User
Joined: Feb 2006
Posts: 479
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From: Sonoma, CA
I assume this is your main tank. That would be a pain and I have not dropped the main tank on my truck. I did yesterday pull the sender from my '76 F250 SC on my aux tank and replace the sunk float. I checked and confirmed that all the wiring was good first and had the float replaced in about 20 minutes. This included testing the sender with an ohm meter to confirm it's operation. The aux tank can be done with the tank in place and is very easy. I also put a new sealing gasket in but used the old locking ring because the new one I got was too loose.
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Freshman User
Joined: Jan 2006
Posts: 45
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From: DFW, Texas
I agree 2 hours labor is somewhate expensive, but the 'ol FD was out to the house once already this year!!! Something about a gas tank and me in the garage & my wife said fork over the $$$
I've found that usually the diagnostics for the gauge & tank problem have been easy, even for me. Good luck.
BTW... 5 gallons of motor oil spreads quickly to the street....the handle broke off the container when I went to take it for proper disposal. The FD sent a rather large truck!!
I've found that usually the diagnostics for the gauge & tank problem have been easy, even for me. Good luck.
BTW... 5 gallons of motor oil spreads quickly to the street....the handle broke off the container when I went to take it for proper disposal. The FD sent a rather large truck!!
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