Gas Gauge/sending unit issues… - The 1947 - Present Chevrolet & GMC Truck Message Board Network

inkslingrrr · 03-08-2023, 10:36 PM

OK, so back to you gurus for some assistance.
I replaced the gas tank in my ‘71 c10 from the behind the seat version to the bed rails kind from LMC. Now with a full tank, the (stock) gauge reads just under half. Tested the sending unit seems to work OK, pulled it out tested it by hand, Can still only get it to read just under half. Where do I start. Should I believe this is the resistors on the old gauge?
Once I learn to post pictures I’ll get some on here

**Palf70Step** · 03-08-2023, 10:40 PM

Check for a good ground to the sending unit. That will mess with the gauge.

inkslingrrr · 03-08-2023, 10:46 PM

Quote:

Originally Posted by Palf70Step

Check for a good ground to the sending unit. That will mess with the gauge.

Sending unit ground is good

**pjmoreland** · 03-08-2023, 11:21 PM

Is the new sender a 0-90 Ohm type? The sender resistance should be around 0 Ohms at empty and 90 Ohms at full.

Did the gauge work correctly with your original sender?

inkslingrrr · 03-08-2023, 11:42 PM

Quote:

Originally Posted by pjmoreland

Is the new sender a 0-90 Ohm type? The sender resistance should be around 0 Ohms at empty and 90 Ohms at full.

Did the gauge work correctly with your original sender?

Yes it sure did

RustyPile · 03-09-2023, 12:23 AM

Quote:

Originally Posted by inkslingrrr

OK, so back to you gurus for some assistance.
I replaced the gas tank in my ‘71 c10 from the behind the seat version to the bed rails kind from LMC. Now with a full tank, the (stock) gauge reads just under half. Tested the sending unit seems to work OK, pulled it out tested it by hand, Can still only get it to read just under half. Where do I start. Should I believe this is the resistors on the old gauge?
Once I learn to post pictures I’ll get some on here

If the circuit is wired correctly and the grounds are good, it sounds like you have the wrong sending unit. With a full tank, a 30 ohm sending unit will read just under 1/2 tank when connected to a 90 ohm gauge.

**pjmoreland** · 03-09-2023, 12:32 AM

Quote:

Originally Posted by inkslingrrr

Yes it sure did

That sure points at the new sender as the problem then.

If you have a multimeter, it would be good to measure the resistance of the sender to see if it has a 0-90 Ohm range.

inkslingrrr · 03-09-2023, 12:57 AM

Quote:

Originally Posted by RustyPile

If the circuit is wired correctly and the grounds are good, it sounds like you have the wrong sending unit. With a full tank, a 30 ohm sending unit will read just under 1/2 tank when connected to a 90 ohm gauge.

So nowhere in LMC catalog do I see a order # for a 90 ohm sender****

**pjmoreland** · 03-09-2023, 02:23 AM

A stock fuel gauge is designed to work with a 90-ohm sender. See post #3 of the following thread for an explanation of how to test the resistance of your LMC sending unit.

https://67-72chevytrucks.com/vboard/...d.php?t=640615

inkslingrrr · 03-09-2023, 11:51 AM

Quote:

Originally Posted by pjmoreland

A stock fuel gauge is designed to work with a 90-ohm sender. See post #3 of the following thread for an explanation of how to test the resistance of your LMC sending unit.

https://67-72chevytrucks.com/vboard/...d.php?t=640615

So yeah, this is test it out as a 0 to 35 ohm sending unit… Now to find the right one or use a fuel bridge, need to thank everybody for their assistance because this is a little bit too techie for this old man!! thanks again

RustyPile · 03-09-2023, 08:48 PM

Quote:

Originally Posted by inkslingrrr

So yeah, this is test it out as a 0 to 35 ohm sending unit… Now to find the right one or use a fuel bridge, need to thank everybody for their assistance because this is a little bit too techie for this old man!! thanks again

What's a fuel bridge?? [EDIT] Never mind, I found the answer...

03-08-2023, 10:36 PM	#1
inkslingrrr Registered User Join Date: Jun 2013 Location: weyburn, sask Posts: 20	Gas Gauge/sending unit issues… OK, so back to you gurus for some assistance. I replaced the gas tank in my ‘71 c10 from the behind the seat version to the bed rails kind from LMC. Now with a full tank, the (stock) gauge reads just under half. Tested the sending unit seems to work OK, pulled it out tested it by hand, Can still only get it to read just under half. Where do I start. Should I believe this is the resistors on the old gauge? Once I learn to post pictures I’ll get some on here

03-08-2023, 10:40 PM	#2
Palf70Step State of Confusion! Join Date: Jul 2002 Location: Gulfport, MS USA Posts: 46,644	Re: Gas Gauge/sending unit issues… Check for a good ground to the sending unit. That will mess with the gauge. __________________ Bill 1970 Chevy Custom/10 LWB Fleetside 2010 Toyota Tacoma PreRunner SR5 Double Cab - DD Member of Louisiana Classic Truck Club (LCTC) Bill's Gallery Life isn't tied with a bow, but it's still a gift. Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God!

03-08-2023, 11:21 PM	#4
pjmoreland Senior Member Join Date: Jan 2005 Location: CA Posts: 5,329	Re: Gas Gauge/sending unit issues… Is the new sender a 0-90 Ohm type? The sender resistance should be around 0 Ohms at empty and 90 Ohms at full. Did the gauge work correctly with your original sender?

03-09-2023, 02:23 AM	#9
pjmoreland Senior Member Join Date: Jan 2005 Location: CA Posts: 5,329	Re: Gas Gauge/sending unit issues… A stock fuel gauge is designed to work with a 90-ohm sender. See post #3 of the following thread for an explanation of how to test the resistance of your LMC sending unit. https://67-72chevytrucks.com/vboard/...d.php?t=640615



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.