Bad Fuel Reading - The 1947 - Present Chevrolet & GMC Truck Message Board Network

lts70 · 10-31-2007, 08:03 PM

When I fill my blazer tank up on my truck the fuel gauge reads ¼ over full capacity. As I drive it around it seems to stay at the ¼ over full to full mark for quite awhile then quickly drops from there. As it works below full the needle sometimes gets a bit jumpy but not always. I would like to know how I can get it to read more accurately. All it is really good for right now is telling me it is full or almost empty. I have the tank bolted directly to the frame so I don’t know how a bad ground could be the problem even though it is the first thing that comes to mind. Thanks.

Old Chevy Mech · 10-31-2007, 08:12 PM

Mine did that, then I dropped the tank & soldered a #10 stranded wire to it and tinned a spot on the frame, drilled a hole and bolted the wire on with a stainless 1/4-20 bolt. I also wound up opening the tank, pulling the sending unit and soldering a tiny spot weld that came undone. In addition I also replaced the sending unit wire with one from LMC Truck. Been working flawlessly since I did that over 5 years ago.

Frank

lts70 · 10-31-2007, 10:32 PM

Where did you solder to on the tank? Is there a specific spot that would work best? Thanks for the info Frank.

Old Chevy Mech · 10-31-2007, 11:19 PM

I put it on top so it would be protected & out of the way.

Frank

68C15 · 11-01-2007, 06:38 AM

sounds to me like the sender is open circuit until the wiper get close to the bottom.

69TowRig · 11-01-2007, 12:27 PM

Quote:

Originally Posted by 68C15

sounds to me like the sender is open circuit until the wiper get close to the bottom.

I fixed my old sending unit on my Blazer by taking the resistor assembly apart and soldering across the open on the wire wind. Then I cleaned up all the contact points that were getting worn and causing the "jumpiness".

After all that work and fixing the float (twice) I gave up and bought a new sender. Now the sender works great but the resistor on the gauge blew. Aargh.

lts70 · 11-01-2007, 12:41 PM

I was not clear in my explanation. The reading does not stay on full then go straight to empty. I just doesn’t seem like it is proportioned right, it seems to stay on ¼ past full to full for a lot longer than it takes to work its way from full to empty. It does gradually make its way down it just seems fast and some times in that middle area from ¾ full to ¼ full it jumps around a bit. I am hopping that it is a grounding problem. I will start there then I will check my printed circuit and wiring back to the tank, then I guess I will fix or change out my sending unit.

Does anyone else have their gas gauge read ¼ past full when toped off, is it normal?

uno67 · 11-01-2007, 12:49 PM

my 68 does the exact same thing your talking about it hasn't really bothered me enough to fix it. just figured it needed a new sending unit. pls post if you find a solution.

68gmsee · 11-01-2007, 01:06 PM

If all the grounding checks and broken wires suggestions don't show a problem I would replace the unit. Especially since the next step would be to remove the gas tank to check the sending unit.

Remember that this is like a rheostat-a variable resistor. It has windings on a pad and a set of contacts that slide up and down on the windings depending on the level of the gas in the tank. These can get broken, worn or dirty.

You may also have a bad fuel guage. I'd start with the easy things first like checking the wires to make sure they're making good contact (don't forget the connector contacts in the dash panel. I've had them get crudded up with buildup also).

Old Chevy Mech · 11-01-2007, 01:11 PM

Quote:

Originally Posted by lts70

I was not clear in my explanation. The reading does not stay on full then go straight to empty. I just doesn’t seem like it is proportioned right, it seems to stay on ¼ past full to full for a lot longer than it takes to work its way from full to empty. It does gradually make its way down it just seems fast and some times in that middle area from ¾ full to ¼ full it jumps around a bit. I am hopping that it is a grounding problem. I will start there then I will check my printed circuit and wiring back to the tank, then I guess I will fix or change out my sending unit.

Does anyone else have their gas gauge read ¼ past full when toped off, is it normal?

Mine on my 70 Blazer does, all the time.

Frank

10-31-2007, 08:12 PM	#2
Old Chevy Mech Keepin it runnin! Join Date: Oct 2007 Location: Deep River, CT Posts: 1,036	Re: Bad Fuel Reading Mine did that, then I dropped the tank & soldered a #10 stranded wire to it and tinned a spot on the frame, drilled a hole and bolted the wire on with a stainless 1/4-20 bolt. I also wound up opening the tank, pulling the sending unit and soldering a tiny spot weld that came undone. In addition I also replaced the sending unit wire with one from LMC Truck. Been working flawlessly since I did that over 5 years ago. Frank __________________ 1970 K-5 4X4 Blazer 1970 K-20 4X4 Long Bed "Liberty Means Responsibility, that is why most men dread it"

10-31-2007, 10:32 PM	#3
lts70 1970 Daily Driver Join Date: Jun 2007 Location: Glenns Ferry IDAHO Posts: 1,037	Re: Bad Fuel Reading Where did you solder to on the tank? Is there a specific spot that would work best? Thanks for the info Frank. __________________ It's not truly yours if you didn't build it yourself or if you don't do your own maintenance.

10-31-2007, 11:19 PM	#4
Old Chevy Mech Keepin it runnin! Join Date: Oct 2007 Location: Deep River, CT Posts: 1,036	Re: Bad Fuel Reading I put it on top so it would be protected & out of the way. Frank __________________ 1970 K-5 4X4 Blazer 1970 K-20 4X4 Long Bed "Liberty Means Responsibility, that is why most men dread it"

11-01-2007, 06:38 AM	#5
68C15 blood type; Retumbo Join Date: Jan 2004 Location: next to my reloading bench Posts: 10,269	Re: Bad Fuel Reading sounds to me like the sender is open circuit until the wiper get close to the bottom.

11-01-2007, 12:41 PM	#7
lts70 1970 Daily Driver Join Date: Jun 2007 Location: Glenns Ferry IDAHO Posts: 1,037	Re: Bad Fuel Reading I was not clear in my explanation. The reading does not stay on full then go straight to empty. I just doesn’t seem like it is proportioned right, it seems to stay on ¼ past full to full for a lot longer than it takes to work its way from full to empty. It does gradually make its way down it just seems fast and some times in that middle area from ¾ full to ¼ full it jumps around a bit. I am hopping that it is a grounding problem. I will start there then I will check my printed circuit and wiring back to the tank, then I guess I will fix or change out my sending unit. Does anyone else have their gas gauge read ¼ past full when toped off, is it normal? __________________ It's not truly yours if you didn't build it yourself or if you don't do your own maintenance. Last edited by lts70; 11-01-2007 at 12:43 PM.

10-31-2007, 08:03 PM	#1
lts70 1970 Daily Driver Join Date: Jun 2007 Location: Glenns Ferry IDAHO Posts: 1,037	Bad Fuel Reading When I fill my blazer tank up on my truck the fuel gauge reads ¼ over full capacity. As I drive it around it seems to stay at the ¼ over full to full mark for quite awhile then quickly drops from there. As it works below full the needle sometimes gets a bit jumpy but not always. I would like to know how I can get it to read more accurately. All it is really good for right now is telling me it is full or almost empty. I have the tank bolted directly to the frame so I don’t know how a bad ground could be the problem even though it is the first thing that comes to mind. Thanks. __________________ It's not truly yours if you didn't build it yourself or if you don't do your own maintenance.

11-01-2007, 12:49 PM	#8
uno67 Registered User Join Date: Mar 2003 Location: Tucson, Az Posts: 185	Re: Bad Fuel Reading my 68 does the exact same thing your talking about it hasn't really bothered me enough to fix it. just figured it needed a new sending unit. pls post if you find a solution.

11-01-2007, 01:06 PM	#9
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: Bad Fuel Reading If all the grounding checks and broken wires suggestions don't show a problem I would replace the unit. Especially since the next step would be to remove the gas tank to check the sending unit. Remember that this is like a rheostat-a variable resistor. It has windings on a pad and a set of contacts that slide up and down on the windings depending on the level of the gas in the tank. These can get broken, worn or dirty. You may also have a bad fuel guage. I'd start with the easy things first like checking the wires to make sure they're making good contact (don't forget the connector contacts in the dash panel. I've had them get crudded up with buildup also).

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