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stuck gauge

Kain

Kain

3/4 ton status
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Mar 16, 2011
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Lubbock Texas
gas gauge decided to be stuck at 1/8 of a tank was working when i parked it. had 3/4 of a tank.
any ideas? It is a new sending unit, installed it when i did my efi swap. unpluged and pluged back in to no avail.
 
found it, run the wire found a bad spot will run new wire in the morning. it rubbed on the frame and corroded
 
I'm never that lucky--every time I've had a gas gauge problem,it was the sending unit....:surepal:
 
well it might be cause i ran a new wire from fire wall to gauge and it says 1/8th of a tank you unplug it and plug it back in after cycling the key while it is unpluged and it works for about 30 seconds. I wish spectere wasn't the only ones that make em
 
Are you sure the sending unit has a good ground ?..

$95 sound pretty steep for a sending unit,when one for my '82 diesel that is more complicated,can be had for about $50 or less (it has the water in fuel sensor and an additional "siphon" nipple for water draining ability..what year & model is your truck?.
 
Problem with Dorman is much of their stuff is re-boxed or from China,you might get a Spectra one in their box,(or worse!)-and pay a lot more..I've also seen a few OEM parts in Dorman boxes too though.

I guess sending units for TBI equipped vehicles are more than diesel or carbed ones,probably due to the fuel pump mounting on them ?..

I have several "good used" ones for carbed trucks and one brand new one,but though I "could" use one on my diesel,I'd lose the water in fuel light and water drain ability--unless I could swap only the rehostat dewhicky off one of the "good" ones,onto the body of my original one maybe..
I've put off dropping the tank until it starts leaking ,it was weeping at the seam but has seemed to stop lately..for now I just write down the mileage on the windshield every time I top off the tank..
 
Simple test to check to see where the problem is. We know that the sending unit goes from 0-90 ohms. If you unplug the sending unit at the tank the gauge should peg out (either empty or full, forget which but it doesn't really matter). Then with the end of the plug that goes to the gauge, take a piece of wire and short the purple wire to ground. The gauge should peg the opposite way.

And another thing you can do is measure the resistance of the sending unit (again, purple wire to ground). And if you're really ambitious you can drain the tank at the fuel filter using the fuel pump and watch the resistance of the sending unit change to verify its functional.
 
well the sending unit is not the problem it read 68 ohms witch is how much gas i have in it just under 3/4 of a tank.
so i get to play chase the short. im going to add a few big grounds to the back of the body to chassy and one op front to make sure im getting good ground then go from there. ill take a pick of em later my brother snaged em some one made em then tossed em, voltmeter says there good so ill use em
 
and thanks for the link, thats how i check em from trial and error over the years with gm cars and trucks(chevys too)
 
anyone know which wire comes out of the firewall plug that is the gas gauge wire?
 
Its usually pink or brown or tan wire,but your year may be different than the 85 and older trucks I've dealt with..best to look at a wiring diagram to be certain..
 
It could be the plug connection on the back of the cluster...
 
I'm going to check that before cutting open the wire loom and getting a new roll of wire and running all new from gauge to tank
 
i added this big ass ground to the tub cause when checking tone with volt meter some parts of the body have tone some dont. so im going to over ground the thing. i had the ground cable and didnt have to spend money.
that thing is bigger than my thumb

photo (6).JPG
 
Hope you shined up the frame and tub with a grinder before bolting the ground strap on...rust,mud,and undercoating is a poor conductor..:D.

I had one older GM truck that refused to charge at times,and if it happened at night,the headlights killed the battery in like a half an hour...sometimes revving the engine up over 3 grand got it to "kick on" and start charging..I replaced the wires to the 2 prong plug on the alternator,made sure they had power,still did it...then I replaced both battery cables,to no avail..

Then a friend asked if I was sure it had good grounds--I said "yeah,look--I have a ground from the battery to the alternator bracket (as GM had it factory)--one at the firewall to a valve cover bolt,and a third ground cable I put from the starter bolt to the frame"..

He took a jumper cable from the negative battery post to the alternator,when I had it running,and no charge showing on a voltmeter (said 12.7 volts)...soon as he touched it to the alternator ,a spark snapped,and the engine slowed down,and the voltmeter started to climb,eventually reaching 14.8 volts!...

I was very surprised--all I can figure was the case of the alternator was old and pasty enough not to make a good enough ground to the brackets...I added a wire to one of the bolts that hold the alternator case together with a ring connector,to the battery negative terminal...it never had another issue!..
 
If the gas gauge worked before you swapped to EFI I would focus your attention back at the tank, whatever you touched specifically. Not likely the issue is at the cluster or anywhere forward of the tank unless you messed with it.
 
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