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Old 12-29-2013, 12:12 AM   #1
jmlloar
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Fuel guage problem

91 Topkick

having problems with the fuel gauge not working.

Gauge is at full.

cant seem to remember if that means it is shorted to ground or broken wire.

Seem to remember it being shorted to ground was buried above full and broken wire was below empty.

Doesn't make sense to me for it to be exactly on full mark with the sending unit unhooked.

Anyone have some input? And/or a wire diagram for it?
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Old 12-29-2013, 10:20 AM   #2
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Re: Fuel guage problem

That should be a short to ground.
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Old 12-29-2013, 11:24 AM   #3
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Re: Fuel guage problem

I was thinking short was towards full, but I always thought a short pushed it way past full. And this one is dead on the full mark. Never seen this problem on newer body style, all of my experience is with 87 back pickups.
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Old 12-29-2013, 11:30 AM   #4
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Re: Fuel guage problem

If the wire to the fuel sending unit is unplugged, the fuel gauge should read over the full mark.
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Old 12-29-2013, 04:09 PM   #5
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Re: Fuel guage problem

So then a corroded wire makes more sense, found many of these on headlight harness and some of the combination switch wires. Truck was a NJ plow truck and salt spreader so it has seen above average winter use.
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Old 12-29-2013, 11:26 PM   #6
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Re: Fuel guage problem

We used to have suburbans come in where the baffle would come lose inside the tank and hold the float up. They would be towed in, out of gas, but the owners thought they had fuel in the tank.

Salt and other chemicals are used here too. So much is on the road in areas now that it leaves a cloud of dust behind vehicles from the pulverized salt on the road. The roads aren’t white with snow, they are white with salt. We are double digits sub zero now, and the salt does not melt anything when it is this cold.
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Old 12-30-2013, 12:08 AM   #7
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Re: Fuel guage problem

As of now the gauge doesn't move. Sending unit is unhooked and stays the same unhooked or shorted to ground, So it looks like I'm looking for a broken wire or terminal instead of a shorted wire. Already tested at the weather pck connector at battery box and no change. Only other connector I can find is inside of cab on the firewall. That's where a wire diagram would be great. Wire harness is nothing like the pickups harness. I have a few extras to add I pulled from a pickup and there is no where to hook them up on the med duty harness.
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Old 12-30-2013, 10:34 AM   #8
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Re: Fuel guage problem

I would do some testing right at the gauge.
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Old 12-30-2013, 12:57 PM   #9
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Re: Fuel guage problem

I have a complete cluster you could have if you want. just cover shipping. it was out of an 89 k1500. if this helps you.
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Old 12-30-2013, 06:40 PM   #10
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Re: Fuel guage problem

Offer is appreciated, but mine is a Topkick and uses a completely different cluster. It has needle type gauges and air brakes.
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Last edited by jmlloar; 12-30-2013 at 06:48 PM.
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Old 12-30-2013, 07:22 PM   #11
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Re: Fuel guage problem

you might have to invest in a repair manual

something like this off ebay(i know yours is diesel tho)

http://www.ebay.com/itm/1992-Chevrol...d71a78&vxp=mtr

actually this one is prob better

http://www.ebay.com/itm/1991-GMC-Top...2216ff&vxp=mtr

this one actually has a diesel supplement, but its a 90

http://www.ebay.com/itm/1990-GMC-Top...27b7cb&vxp=mtr
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Last edited by burkey05; 12-30-2013 at 07:32 PM. Reason: new info
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Old 12-30-2013, 08:01 PM   #12
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Re: Fuel guage problem

Quote:
Originally Posted by burkey05 View Post
you might have to invest in a repair manual

something like this off ebay(i know yours is diesel tho)

http://www.ebay.com/itm/1992-Chevrol...d71a78&vxp=mtr

actually this one is prob better

http://www.ebay.com/itm/1991-GMC-Top...2216ff&vxp=mtr

this one actually has a diesel supplement, but its a 90

http://www.ebay.com/itm/1990-GMC-Top...27b7cb&vxp=mtr
Watching the middle one, but don't have the extra $40 right now.
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Old 12-30-2013, 11:55 PM   #13
54 jimmy
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Re: Fuel guage problem

well I tried. good luck tracking the problem down.
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1996 chevy k1500 reg cab 4x4(daily driver)totaled
2008jeep patriot (wife's daily driver
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2011 chevy 1500 crew cab ltz (daily driver)
1996 chevy 1500 reg cab 4x4 project sold
2006 pontiac grand prix gxp (daily work commuter)
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Old 12-31-2013, 09:42 AM   #14
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Re: Fuel guage problem

If the needle isnt "past full" its also possible the float in the tank is hung/stuck. A rubber mallet and a half a tank or less "may" fix that, allowing it to settle.

The float arms can also pinch on the pump hanger, causing same problem.
As u check to see if the connections are good, take a mallet /w/ you.
Also could be "pig tail"
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Old 12-31-2013, 10:20 AM   #15
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Re: Fuel guage problem

Is a Topkick a 4500? I have most wire/d up to the 3500s. There haynes style but if any will help ill post what you want.
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Old 12-31-2013, 08:07 PM   #16
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Re: Fuel guage problem

Quote:
Originally Posted by 400sbctruck View Post
If the needle isnt "past full" its also possible the float in the tank is hung/stuck. A rubber mallet and a half a tank or less "may" fix that, allowing it to settle.

The float arms can also pinch on the pump hanger, causing same problem.
As u check to see if the connections are good, take a mallet /w/ you.
Also could be "pig tail"
See previous posts, Sending unit is not connected to harness. Testing at the wire and at the connector from the main harness and no change.
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Old 12-31-2013, 08:10 PM   #17
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Re: Fuel guage problem

Quote:
Originally Posted by dragginmetal View Post
Is a Topkick a 4500? I have most wire/d up to the 3500s. There haynes style but if any will help ill post what you want.
The topkick starts at 4500. Mine is a 7000. Pretty much everything is slightly different than both the 1500-3500 and 3500HD trucks. The wire harness only shares stuff like the turn signal switch and headlight switch. Main harness is completely different.
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