Gauge shows too full. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

bluec10 · 10-08-2004, 12:23 AM

Just read a thread by bozracing - his gauge always reads empty. I have the opposite problem - my gauge never gets to empty. When the tank is completely full it is about 1/2 inch beyond the full mark. Any ideas?

BraveDave · 10-08-2004, 12:28 AM

just pretend you have a tank and a quarter......

(sorry...couldn't help myself)

sdkid · 10-08-2004, 12:40 AM

Does it ever move. if always says over full, the wire to the sending unit is open somewhere alomg the line.

Longhorn Man · 10-08-2004, 06:06 AM

Actually, wouldn't the wire be grounded somewhere?

Brainchild · 10-08-2004, 09:00 AM

No once you unplug it from te sender it pegs out.

Russell · 10-08-2004, 09:50 AM

If you want, you can put a resistor / capacitator into the line to adjust the sending unit's signal so it reads properly. Thats what I am doing with my Blazer tank to get it to read properly becuase it sits slightly crooked in my frame rails

olblue60@aol.com · 10-08-2004, 09:56 AM

Mine was above full when I purchased my truck.It ran out gas soon after while idleing in my driveway. I filled it up and the guage worked fine,that tank of gas. from there on it is back above full all of the time. Is that what yours is doing?Anyone know whats up?
John

chickenwing · 10-08-2004, 10:46 AM

When I disconnected my fuel sending wire my gauge did peg out also, guess they are the opposite of temp gauges. Maybe the connector to your sending unit is corroded increasing the resistance to your gauge. That would explain constant high readings. If the readings are high only when full then variable resister is probably worn out in full position. If that is't the ticket either maybe the gauge is just fargged up.

Southpa · 10-08-2004, 10:47 AM

Gauge always reading empty usually means that the float has a hole and is full of gas. Gauge reading too full might be electrical problem. Even if the wire to the sender is still connected, check it with an ohmmeter for continuity, could be broken somewhere.

JimKshortstep4x4 · 10-08-2004, 12:59 PM

Disconnect the brown sending unit wire from the the fuse panel and measure the resistance. The ohm reading should be between 0 and 90 ohms, (0 being empty, 90 being full). If the reading is over approximately 90 ohms then the problem is probably in the sending unit or wiring. If the reading is for example 45 ohms and the dash gauge reading is well over 1/2 tank then the problem is in the dash gauge, (the resistor on the gauge, the needle has been removed and reinstalled in the wrong location, or the gauge itself is bad).

Jim

PrimeredThunder · 10-08-2004, 01:03 PM

I had to replace the sending unit in my fuel cell because it died on me, so after doing so and wiring the truck up, I found the needle is off a bit. WHen the tank is full, its about 1/2" past the full marker, but I have a feeling empty is at about 1/4 tank. I havent ran the truck out of gas yet, but when i get low the lowest I've ever seen the needle go is about 1/8" under 1/4 of a tank....I think it just needs adjusted??

Kenny

71-longbed · 10-08-2004, 01:46 PM

when i drained the tank to replace the rubber gas hoses ... i ran it until the guage said empty and then drained 4 gallons .. good thing i had extra milk jugs laying around ..just in case ... i've also seen my gauge about 1/4 inch about full .... i dont know what its trip is ....sorry for the meaningless ramble

sdkid · 10-08-2004, 01:51 PM

They tend to break where the wire runs under the step plate(on mine anyway). Unhook both ends and ohm ckeck it.

bluec10 · 10-08-2004, 09:24 PM

Thanks for all the help - especially the ohm readings. The gauge does move as the tank goes down. I'm going to start by cleaning the connection to the sender.

In my other truck the brown wire that ran under the sill plate was hacked up due to a wrecked sill plate. On this truck the floor is in great shape, so I have my doubts.

These gauges are really simple things - do they get wrecked that often?

Brainchild · 10-08-2004, 10:44 PM

If all else fails you can yank the sender out,and carefully bend the tabs out where you can pull the rectangle box off.There may be a bunch of crud in there causing it to be flaky.I have done this several times and fixed them.In fact fixed the nonworking one in the 71 a couple of days ago.

If it's been sitting a while,the old gas varnishes,and the sediment gums up the contacts inside the sender.It's easy to take apart,just tread lightly,those little tabs break right off

It could be that someone else hasd had it out before and bent the float arm and now it reads wrong.Not sure,but it is an idea

bluec10 · 10-11-2004, 10:33 PM

The truck has been sitting for a looong time. Good suggestion.

10-08-2004, 12:23 AM	#1
bluec10 Registered User Join Date: Apr 2002 Location: Manitoba, Canada Posts: 663	Gauge shows too full. Just read a thread by bozracing - his gauge always reads empty. I have the opposite problem - my gauge never gets to empty. When the tank is completely full it is about 1/2 inch beyond the full mark. Any ideas? __________________ Present: 2015 Tacoma. Yeah, not a GM, but I love it. 1969 GMC 32,000 - fix, drive, relax, fix... 2019 BMW R1250 GSA - Yahoooooooo 1979 Honda GL 1000 - retro touring at its best. Past: '05 Sierra 4x4 - Had 270,000 KM and running well when it was written-off by a stop sign runner. '94 F-150 from the "F word" company. I'll admit it...good truck. Sold what was left of it for $800 to a guy who came to pick it up at 11:00 PM with cash in hand. Hmm. '79 Sierra Grande (Black) organ donor - perfect rebuildable 4-bolt 350 and a good TH350. '76 Sierra Grande (Orange) - hate isn't too strong a word. Kid who bought it turned it into a hot rod. '68 C-10 R.I.P. - Dad's old truck...too far gone to resurrect. '59 C-50 - with hoist. Truck is gone, wife isn't. Nuff said.

10-08-2004, 12:28 AM	#2
BraveDave Registered User Join Date: Dec 2002 Location: Magnolia, Texas Posts: 336	just pretend you have a tank and a quarter...... (sorry...couldn't help myself) __________________ '72 Chevy Cheyenne Super, '56 Chevy Bel Air,'56 Chevy Nomad, '61 Chevy Impala, '64 Cadillac Fleetwood, 1966 Thunderbird Convertible

10-08-2004, 09:00 AM	#5
Brainchild Still drivin' a Rat Rod Join Date: Sep 2004 Location: Monett Missouri Posts: 4,925	No once you unplug it from te sender it pegs out. __________________ Rusty Member #13872 Instead of saying.....you are a discomfort in the back of my front.....one should be able to say...... you are a pain in the a$# 71 GMC LWB 49 Chevy 85 Chevy G20 Check out my website

10-08-2004, 09:50 AM	#6
Russell Professional Grade Join Date: May 2003 Location: Fort McMurray, Alberta Posts: 7,915	If you want, you can put a resistor / capacitator into the line to adjust the sending unit's signal so it reads properly. Thats what I am doing with my Blazer tank to get it to read properly becuase it sits slightly crooked in my frame rails __________________ 1995 Chevrolet 2 Door Tahoe (6.6L LBZ Duramax / ZF6 / NP241 with 1 ton solid axle swap)

10-08-2004, 09:56 AM	#7
olblue60@aol.com member Join Date: Dec 2003 Location: Silver Spring Md.20901 Posts: 2,031	Mine was above full when I purchased my truck.It ran out gas soon after while idleing in my driveway. I filled it up and the guage worked fine,that tank of gas. from there on it is back above full all of the time. Is that what yours is doing?Anyone know whats up? John __________________ 1967 C/K10 Chevy Panel 1968 C/K20 Chevy Pickup 1968 C/K10 Chevy Suburban 1941 Chevy Sedan Delivery 1960 Chevy Sedan Delivery 1972 Camaro SS 396 #s matching 1971 Harley FX Superglide Last edited by olblue60@aol.com; 10-08-2004 at 09:59 AM.

10-08-2004, 12:40 AM	#3
sdkid Registered User Join Date: Sep 2004 Location: Pierre SD Posts: 1,533	Does it ever move. if always says over full, the wire to the sending unit is open somewhere alomg the line.

10-08-2004, 06:06 AM	#4
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Actually, wouldn't the wire be grounded somewhere?

10-08-2004, 10:46 AM	#8
chickenwing Lovin' Life in Miss.! Join Date: Mar 2004 Location: Puckett, Mississippi Posts: 1,937	When I disconnected my fuel sending wire my gauge did peg out also, guess they are the opposite of temp gauges. Maybe the connector to your sending unit is corroded increasing the resistance to your gauge. That would explain constant high readings. If the readings are high only when full then variable resister is probably worn out in full position. If that is't the ticket either maybe the gauge is just fargged up. __________________ The truck... you hear that? No really, you did hear that?!!!

10-08-2004, 10:47 AM	#9
Southpa Registered User Join Date: May 2000 Location: Victoria, BC, Canada Posts: 2,410	Gauge always reading empty usually means that the float has a hole and is full of gas. Gauge reading too full might be electrical problem. Even if the wire to the sender is still connected, check it with an ohmmeter for continuity, could be broken somewhere. __________________ 1970 GMC 1500 Custom Original 350/TH350 Victoria, BC, Canada You can wish in one hand and crap in the other. See which one gets filled first.

10-08-2004, 12:59 PM	#10
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Disconnect the brown sending unit wire from the the fuse panel and measure the resistance. The ohm reading should be between 0 and 90 ohms, (0 being empty, 90 being full). If the reading is over approximately 90 ohms then the problem is probably in the sending unit or wiring. If the reading is for example 45 ohms and the dash gauge reading is well over 1/2 tank then the problem is in the dash gauge, (the resistor on the gauge, the needle has been removed and reinstalled in the wrong location, or the gauge itself is bad). Jim

10-08-2004, 01:03 PM	#11
PrimeredThunder Back from the Dead Join Date: Dec 2001 Location: Salem, Oregon Posts: 522	I had to replace the sending unit in my fuel cell because it died on me, so after doing so and wiring the truck up, I found the needle is off a bit. WHen the tank is full, its about 1/2" past the full marker, but I have a feeling empty is at about 1/4 tank. I havent ran the truck out of gas yet, but when i get low the lowest I've ever seen the needle go is about 1/8" under 1/4 of a tank....I think it just needs adjusted?? Kenny __________________ The only Carb that matters to me is the one under my hood! Salem, Oregon

10-08-2004, 01:46 PM	#12
71-longbed Its Magically Delicious Join Date: Jan 2003 Location: oregon Posts: 2,398	when i drained the tank to replace the rubber gas hoses ... i ran it until the guage said empty and then drained 4 gallons .. good thing i had extra milk jugs laying around ..just in case ... i've also seen my gauge about 1/4 inch about full .... i dont know what its trip is ....sorry for the meaningless ramble __________________ 71 C10 LWB 350sbc -TH350 12 bolt 3.42 Posi Of all my favorite things to do, The utmost is to have a brew. My love grows for my foamy friend, with each thirst-quenching elbow bend. Beer so frosty, smooth, and cold it's paradise pure liquid gold. Yes beer means many things to me that's all for now cus I gotta pee.

10-08-2004, 01:51 PM	#13
sdkid Registered User Join Date: Sep 2004 Location: Pierre SD Posts: 1,533	They tend to break where the wire runs under the step plate(on mine anyway). Unhook both ends and ohm ckeck it.

10-08-2004, 09:24 PM	#14
bluec10 Registered User Join Date: Apr 2002 Location: Manitoba, Canada Posts: 663	Thanks for all the help - especially the ohm readings. The gauge does move as the tank goes down. I'm going to start by cleaning the connection to the sender. In my other truck the brown wire that ran under the sill plate was hacked up due to a wrecked sill plate. On this truck the floor is in great shape, so I have my doubts. These gauges are really simple things - do they get wrecked that often? __________________ Present: 2015 Tacoma. Yeah, not a GM, but I love it. 1969 GMC 32,000 - fix, drive, relax, fix... 2019 BMW R1250 GSA - Yahoooooooo 1979 Honda GL 1000 - retro touring at its best. Past: '05 Sierra 4x4 - Had 270,000 KM and running well when it was written-off by a stop sign runner. '94 F-150 from the "F word" company. I'll admit it...good truck. Sold what was left of it for $800 to a guy who came to pick it up at 11:00 PM with cash in hand. Hmm. '79 Sierra Grande (Black) organ donor - perfect rebuildable 4-bolt 350 and a good TH350. '76 Sierra Grande (Orange) - hate isn't too strong a word. Kid who bought it turned it into a hot rod. '68 C-10 R.I.P. - Dad's old truck...too far gone to resurrect. '59 C-50 - with hoist. Truck is gone, wife isn't. Nuff said.

10-08-2004, 10:44 PM	#15
Brainchild Still drivin' a Rat Rod Join Date: Sep 2004 Location: Monett Missouri Posts: 4,925	If all else fails you can yank the sender out,and carefully bend the tabs out where you can pull the rectangle box off.There may be a bunch of crud in there causing it to be flaky.I have done this several times and fixed them.In fact fixed the nonworking one in the 71 a couple of days ago. If it's been sitting a while,the old gas varnishes,and the sediment gums up the contacts inside the sender.It's easy to take apart,just tread lightly,those little tabs break right off It could be that someone else hasd had it out before and bent the float arm and now it reads wrong.Not sure,but it is an idea __________________ Rusty Member #13872 Instead of saying.....you are a discomfort in the back of my front.....one should be able to say...... you are a pain in the a$# 71 GMC LWB 49 Chevy 85 Chevy G20 Check out my website Last edited by Brainchild; 10-08-2004 at 10:48 PM.



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10-11-2004, 10:33 PM	#16
bluec10 Registered User Join Date: Apr 2002 Location: Manitoba, Canada Posts: 663	The truck has been sitting for a looong time. Good suggestion. __________________ Present: 2015 Tacoma. Yeah, not a GM, but I love it. 1969 GMC 32,000 - fix, drive, relax, fix... 2019 BMW R1250 GSA - Yahoooooooo 1979 Honda GL 1000 - retro touring at its best. Past: '05 Sierra 4x4 - Had 270,000 KM and running well when it was written-off by a stop sign runner. '94 F-150 from the "F word" company. I'll admit it...good truck. Sold what was left of it for $800 to a guy who came to pick it up at 11:00 PM with cash in hand. Hmm. '79 Sierra Grande (Black) organ donor - perfect rebuildable 4-bolt 350 and a good TH350. '76 Sierra Grande (Orange) - hate isn't too strong a word. Kid who bought it turned it into a hot rod. '68 C-10 R.I.P. - Dad's old truck...too far gone to resurrect. '59 C-50 - with hoist. Truck is gone, wife isn't. Nuff said.

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