help on fuel sending unit

utah86gmc · 03-28-2006, 09:51 PM

I have an 1986 1/2 ton 4WD since I had it the fuel gauge has not worked. It has the dual tanks and no matter what tank its on the needle sits horizontal left. I tried changing the gauge since it was cheap and easy no luck.

Anyone have a detailed way to check the sending unit. They are over $100 bucks before I waste my money I would like to try to trouble shoot it and be sure.

92BlueZ71 · 03-29-2006, 04:38 PM

check all your wires from the gauge to the tanks and if they look tip/top then i say just probably go ahead and change your sending unit. thats what i would do

chevyguy · 03-29-2006, 09:00 PM

HUH?^^ What do you mean. To properly check wires you should check resistance with meter, Use an OHM meter and make sure there isnt a broken wire or a corroded wire inside the sheilding. Just looking at then doesnt rule out anything especially if you live up north . More than likely the switch mechanism under the truck at the switchover from one tank to another if it isnt working on either tank. Sending unit is more than likely not the problem, They usually done both fail at the same time.

92BlueZ71 · 03-29-2006, 09:44 PM

worked on my 62 but i guess thats ancient times. just went through and fixed the bad spots in the wiring and it fixed it. aint the most accurate thing but it works alright.

chevyguy · 03-29-2006, 10:16 PM

Not alot different than this above mentioned truck, Just has a tank switch

utah86gmc · 03-30-2006, 08:18 PM

Chevyguy,

So if I understand you right each sending unit has a separate set of wires to the tank switch, then one set to the gauge.
I know the tank switch will switch the fuel supply line properly but the electrical contacts that change the signal to the gauge could be bad. Thanks I never thought of that.

DUH!!

I have not checked how many wires go to each unit it must be at least 2 a 12v hot and the returm from the resistor or potentiometer whatever is in the sending unit. I was wondering if anyone knew what ohm reading the unit should give? for example 400 ohms full 75 ohms empty etc.
Also what readings should I get thru the sending unit I guess I can just check continuity to make sure there are no breaks in the circuit but the proper ohms/resistance would be really helpful.

Again thanks for you guys help

chevyguy · 03-30-2006, 11:16 PM

I dont know right off hand, But as i stated before i dont think both would go bad at the same time. It could happen, but not likely.

03-28-2006, 09:51 PM	#1
utah86gmc Junior Member Join Date: Mar 2006 Posts: 3	help on fuel sending unit I have an 1986 1/2 ton 4WD since I had it the fuel gauge has not worked. It has the dual tanks and no matter what tank its on the needle sits horizontal left. I tried changing the gauge since it was cheap and easy no luck. Anyone have a detailed way to check the sending unit. They are over $100 bucks before I waste my money I would like to try to trouble shoot it and be sure.

03-29-2006, 04:38 PM	#2
92BlueZ71 Senior Member Join Date: Feb 2006 Posts: 117	check all your wires from the gauge to the tanks and if they look tip/top then i say just probably go ahead and change your sending unit. thats what i would do __________________ CHEVROLET "Friends don't let friends drive a Ford" '92 Ext. Cab Short-Wide Z71 '62 Short-Stepside C10

03-29-2006, 09:00 PM	#3
chevyguy Senior Member Join Date: Sep 2005 Location: ALABAMA Posts: 3,370	HUH?^^ What do you mean. To properly check wires you should check resistance with meter, Use an OHM meter and make sure there isnt a broken wire or a corroded wire inside the sheilding. Just looking at then doesnt rule out anything especially if you live up north . More than likely the switch mechanism under the truck at the switchover from one tank to another if it isnt working on either tank. Sending unit is more than likely not the problem, They usually done both fail at the same time. __________________ Friends dont let friends use body lifts USMC 92-96 USCG 98 to present

03-29-2006, 09:44 PM	#4
92BlueZ71 Senior Member Join Date: Feb 2006 Posts: 117	worked on my 62 but i guess thats ancient times. just went through and fixed the bad spots in the wiring and it fixed it. aint the most accurate thing but it works alright. __________________ CHEVROLET "Friends don't let friends drive a Ford" '92 Ext. Cab Short-Wide Z71 '62 Short-Stepside C10

03-29-2006, 10:16 PM	#5
chevyguy Senior Member Join Date: Sep 2005 Location: ALABAMA Posts: 3,370	Not alot different than this above mentioned truck, Just has a tank switch __________________ Friends dont let friends use body lifts USMC 92-96 USCG 98 to present

03-30-2006, 08:18 PM	#6
utah86gmc Junior Member Join Date: Mar 2006 Posts: 3	Chevyguy, So if I understand you right each sending unit has a separate set of wires to the tank switch, then one set to the gauge. I know the tank switch will switch the fuel supply line properly but the electrical contacts that change the signal to the gauge could be bad. Thanks I never thought of that. DUH!! I have not checked how many wires go to each unit it must be at least 2 a 12v hot and the returm from the resistor or potentiometer whatever is in the sending unit. I was wondering if anyone knew what ohm reading the unit should give? for example 400 ohms full 75 ohms empty etc. Also what readings should I get thru the sending unit I guess I can just check continuity to make sure there are no breaks in the circuit but the proper ohms/resistance would be really helpful. Again thanks for you guys help

03-30-2006, 11:16 PM	#7
chevyguy Senior Member Join Date: Sep 2005 Location: ALABAMA Posts: 3,370	I dont know right off hand, But as i stated before i dont think both would go bad at the same time. It could happen, but not likely. __________________ Friends dont let friends use body lifts USMC 92-96 USCG 98 to present

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