fuel gauge problem - The 1947 - Present Chevrolet & GMC Truck Message Board Network

ssjones · 07-31-2005, 01:18 AM

Need some help. I installed a blazer tank last week with a new sending unit. The truck is showing 1/8 of a tank and should show empty. The gauge doesn’t show full when the tank is full. Is there some way to calibrate the gauge?
Thanks

Sweet72 · 07-31-2005, 10:13 AM

Do this simple test...With the key in "on", take the sending unit wire off and using a jumper wire, ground it to the frame, the gauge should go full travel, (can't remember empty or full) then, remove the wire and the gauge should go full travel the other direction then you will know your gauge and wiring are good.

Now to the sending unit. Disconnect battery neg. (safety reasons) Remove the sender from tank, with an ohm meter check for 90 ohms with the float at full travel one direction, and 0 ohms with the float at full travel the other direction (once again my memory fails me).

As far as calibration goes, the only method I know of is to bend the float arm, although I've heard of guys pulling the needle off the gauge with the tank full and re-indexing it to the "Full" mark, and then checking Empty with no fuel in tank, but from what I've heard this is not always a successful method.

ssjones · 07-31-2005, 01:39 PM

I think I can try the grounding the sending unit wire to test the gauge. Can I just ground it from under the dash. I did run new wire back to the sending unit. The sending unit is new. I know some parts are bad from the box but I would have to remove my bed from the truck to remove the sending unit. I dont have an easy way of doing that.

I had a buddy in school that used to check his gas with a broom stick... ha ha..

jhow66 · 07-31-2005, 02:24 PM

Is your tank grounded good to frame? If grounding does not make it work change the small resistor on back of gauge.
www.fix-a-gauge.com

matthufham · 07-31-2005, 03:25 PM

have you ever taken the needle off? it's easy to do that and put it back close to the same spot but not perfect.

ssjones · 07-31-2005, 03:49 PM

jhow66 - I do have the tank grounded but will check that out. I have heard about the small resistor on the gauge being an issue. I dont know if the gauge worked that well since I have owned the truck. I never ran it to empty but would fill up once I heard the slosh of tank in the cab. Dont have that slosh sound anymore so I ran out of gas on the freeway and the gauge was at 1/8 of a tank.

matthufham - I have never taken the needle off. But I know I dont want to run out of gas again. Too hot here in AZ to be stuck with no gas on the freeway.

Sweet72 · 07-31-2005, 08:00 PM

Yes you can ground the sending unit wire from under the dash, but it obviously won't verify that the wire from there to the tank is good. Having to pull the bed to get to it is a PITA. Good luck

chickenwing · 08-01-2005, 11:46 AM

I could see that the tank might not be grounded. On my 74 blazer tank there is a bonding wire mounted on the collar on the tank. Run that to a good chassis ground.

ssjones · 08-01-2005, 02:02 PM

There is a ground wire that comes off the sending unit that I have grounded.
Should there be another ground?

Thanks.

chickenwing · 08-01-2005, 02:24 PM

Nope. Just make sure the one ya got is on clean mounting surfaces. Sounds like everyone else has ya steered on the right track.

07-31-2005, 01:18 AM	#1
ssjones Registered User Join Date: Mar 2005 Location: Scottsdale, Arizona Posts: 98	fuel gauge problem Need some help. I installed a blazer tank last week with a new sending unit. The truck is showing 1/8 of a tank and should show empty. The gauge doesn’t show full when the tank is full. Is there some way to calibrate the gauge? Thanks __________________ 1972 Chevy Cheyenne 20 1979 Chevy Camaro 2007 Chevy Avalanche 2005 Mini Cooper

07-31-2005, 10:13 AM	#2
Sweet72 Registered User Join Date: Nov 2003 Location: Alexandria, VA Posts: 1,534	Do this simple test...With the key in "on", take the sending unit wire off and using a jumper wire, ground it to the frame, the gauge should go full travel, (can't remember empty or full) then, remove the wire and the gauge should go full travel the other direction then you will know your gauge and wiring are good. Now to the sending unit. Disconnect battery neg. (safety reasons) Remove the sender from tank, with an ohm meter check for 90 ohms with the float at full travel one direction, and 0 ohms with the float at full travel the other direction (once again my memory fails me). As far as calibration goes, the only method I know of is to bend the float arm, although I've heard of guys pulling the needle off the gauge with the tank full and re-indexing it to the "Full" mark, and then checking Empty with no fuel in tank, but from what I've heard this is not always a successful method. __________________ '72 GMC SWB C1500 Custom, frame-off in progress. 383 SBC, 9:1CR, Comp Cams XE262H, Scat internal balanced crank, Eagle SIR 6" rods, Keith Black dish pistons, Dart Iron Eagle 72/180 heads, Weiand Stealth intake, Stewart stage I water pump, Holley 4bbl vac sec, TH350 with B&M Shift Improver Kit. 12 bolt positraction. Last edited by Sweet72; 07-31-2005 at 10:20 AM.

07-31-2005, 01:39 PM	#3
ssjones Registered User Join Date: Mar 2005 Location: Scottsdale, Arizona Posts: 98	I think I can try the grounding the sending unit wire to test the gauge. Can I just ground it from under the dash. I did run new wire back to the sending unit. The sending unit is new. I know some parts are bad from the box but I would have to remove my bed from the truck to remove the sending unit. I dont have an easy way of doing that. I had a buddy in school that used to check his gas with a broom stick... ha ha.. __________________ 1972 Chevy Cheyenne 20 1979 Chevy Camaro 2007 Chevy Avalanche 2005 Mini Cooper

07-31-2005, 02:24 PM	#4
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	Is your tank grounded good to frame? If grounding does not make it work change the small resistor on back of gauge. www.fix-a-gauge.com __________________ 56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer

07-31-2005, 03:49 PM	#6
ssjones Registered User Join Date: Mar 2005 Location: Scottsdale, Arizona Posts: 98	jhow66 - I do have the tank grounded but will check that out. I have heard about the small resistor on the gauge being an issue. I dont know if the gauge worked that well since I have owned the truck. I never ran it to empty but would fill up once I heard the slosh of tank in the cab. Dont have that slosh sound anymore so I ran out of gas on the freeway and the gauge was at 1/8 of a tank. matthufham - I have never taken the needle off. But I know I dont want to run out of gas again. Too hot here in AZ to be stuck with no gas on the freeway. __________________ 1972 Chevy Cheyenne 20 1979 Chevy Camaro 2007 Chevy Avalanche 2005 Mini Cooper

07-31-2005, 03:25 PM	#5
matthufham Registered User Join Date: Feb 2005 Location: Carl Junction, Missouri Posts: 2,061	have you ever taken the needle off? it's easy to do that and put it back close to the same spot but not perfect.

07-31-2005, 08:00 PM	#7
Sweet72 Registered User Join Date: Nov 2003 Location: Alexandria, VA Posts: 1,534	Yes you can ground the sending unit wire from under the dash, but it obviously won't verify that the wire from there to the tank is good. Having to pull the bed to get to it is a PITA. Good luck __________________ '72 GMC SWB C1500 Custom, frame-off in progress. 383 SBC, 9:1CR, Comp Cams XE262H, Scat internal balanced crank, Eagle SIR 6" rods, Keith Black dish pistons, Dart Iron Eagle 72/180 heads, Weiand Stealth intake, Stewart stage I water pump, Holley 4bbl vac sec, TH350 with B&M Shift Improver Kit. 12 bolt positraction.

08-01-2005, 11:46 AM	#8
chickenwing Lovin' Life in Miss.! Join Date: Mar 2004 Location: Puckett, Mississippi Posts: 1,937	I could see that the tank might not be grounded. On my 74 blazer tank there is a bonding wire mounted on the collar on the tank. Run that to a good chassis ground.

08-01-2005, 02:02 PM	#9
ssjones Registered User Join Date: Mar 2005 Location: Scottsdale, Arizona Posts: 98	There is a ground wire that comes off the sending unit that I have grounded. Should there be another ground? Thanks. __________________ 1972 Chevy Cheyenne 20 1979 Chevy Camaro 2007 Chevy Avalanche 2005 Mini Cooper

08-01-2005, 02:24 PM	#10
chickenwing Lovin' Life in Miss.! Join Date: Mar 2004 Location: Puckett, Mississippi Posts: 1,937	Nope. Just make sure the one ya got is on clean mounting surfaces. Sounds like everyone else has ya steered on the right track.



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