Need Help w Fuel Gauge Please - Tried a Search

[DeadheadNM]

The fuel gauge in my 72 Blazer reads 1/2 full with a full tank and when I disconnect the tan harness wire from the fuse block the gauge needle swings way over to the 5:30 position. I didn't realize it could peg that far to the right. Could this be a grounding issue? Bad printed circuit?

Just before my recent move we swapped in a rebuilt all OEM cluster. Prior to that, the gauge was working fine when I drove the Blazer from So Cal to Albuquerque. The sending unit was replaced when the PO had the Hickey tank cleaned/coated. We didn't muck with the tank.

Appreciate any help. I was unsuccessful in searching for an answer.

Thanks, Pete

[Molberg]

I would start by verifying you have a good ground to the sending unit itself. Make some jumper wires out of surplus wire. Connect to a good ground and verify first. Then run a jumper to replace our tan signal wire. Mice chewed through mine. Will rule out ground and signal wires. Hopefully your upgraded gauge was within the resistances required to operate.

[VetteVet]

5:30 is a little far for the gauge to swing to the right. That indicates that the resistor on the back of the gauge might be incorrect. Try running a ground wire to the terminal on the fuse panel and see if the fuel gauge swings all the way back to empty. If it does then pull the wire off at the sending unit and check for the 5:30 position on the gauge again. If it does the same then ground the wire to the sending unit on a good ground and check again for empty. If it goes to empty then the problem is in the tank ground or sending unit.
If you can, pull the sending unit and ground the flange and with the tan wire connected, move the float arm through it's travel and see if the gauge follows the travel. If it does you may have a bad ground on the tank or the float arm may be restricted in it's movement. A possibility is that the float may have a pinhole in it and it will only lift to the half tank mark because it has fuel in it.

[Molberg]

The wrong sending unit installed previously will send you for a loop as well. Not sure about your application.... Mine (1970) has a range of 0-90 ohms(I believe) to operate properly with the factory gauge. Much outside of that... Your needle will be all over the map

[DeadheadNM]

Thanks for the help guys - I really appreciate it. Just to clarify, when I run a ground to the terminal at the fuse panel I'm grounding the tan wire while its still plugged into the spade or unplug the tan wire first?

Since my garage space is limited I put the Blazer in the storage unit this afternoon and drove the K20 home to tinker. Both were just delivered last Sunday after waiting ~8 weeks. I'll trouble shoot the Blazer over the Thanksgiving holiday and get back with you. On my drive home I learned one of my T3's in the K20 lost a low beam and the oil pressure gauge we converted to electronic isn't working (or the oil pump is out on my rebuilt motor with 50 miles). Doh!!

[VetteVet]

Unplug it first so you'll be isolated from the sending unit altogether. If you get empty then plug it back in and then unplug it from the sending unit and ground it to a good ground to see if you still get empty on the gauge.

[DeadheadNM]

Originally Posted by VetteVet

Unplug it first so you'll be isolated from the sending unit altogether. If you get empty then plug it back in and then unplug it from the sending unit and ground it to a good ground to see if you still get empty on the gauge.

Check - thanks again!

[Average Joe]

Great info here. I still need to get my fuel gauge working.

[DeadheadNM]

Well - the fuel gauge seems to work now and I didn't touch a thing. I'll trace the grounds and make sure all are secure. Also got the oil pressure gauge working on the K20 (loose connection). Greatly appreciate the help guys, thanks. Pete

[zeldman]

Originally Posted by DeadheadNM

Well - the fuel gauge seems to work now and I didn't touch a thing.

Those pesky gremlins again..... all named Murphy I bet.

[DeadheadNM]

Originally Posted by zeldman

Those pesky gremlins again..... all named Murphy I bet.

You got it! Have some green chile stew at Earl's for me! Best, Pete

[mpierce9]

Excellent conversation, Thank you. I'm working on the same thing.

[DeadheadNM]

So spring is here and ran out of gas after clocking 90 miles on a full 37 gallon Hickey tank of non-ethanol 91 octane - guess my occasional winter storage warm ups burned a lot of fuel

Anyway, I dug into trouble shooting what I thought was a resolved problem with the fuel gauge.

I ran out with a little more than half a tank on the gauge. When I yank the tan sending unit wire the gauge looks like this:

[DeadheadNM]

When I ground that slot on the fuse block I get this - will not go all the way to empty:

[DeadheadNM]

And with I'd guess 1/2 to 3/4 tank looks like this (sender tan wire on):

[DeadheadNM]

It's as if the gauge is off by 45 degrees or so. Does this imply a resistor problem with the gauge itself?

This is a clock tach dash built by a board member. The fuel gauge worked fine with the original cluster - not so with this rebuilt cluster so don't suspect ground or sender unit problem. If gauge issue, would a resistor swap likely result in a working gauge??

[TBONE1964]

Hi Pete,

Was your gauge position correct when the tank was full?

My thought is when they restored the cluster they may have removed the needle from the gas gauge. This is a no no because it is hard to reference where it should be placed when they put it back on after painting.

Not 100% sure if that is your problem but it is possible.

[DeadheadNM]

Originally Posted by TBONE1964

Hi Pete,

Was your gauge position correct when the tank was full?

My thought is when they restored the cluster they may have removed the needle from the gas gauge. This is a no no because it is hard to reference where it should be placed when they put it back on after painting.

Not 100% sure if that is your problem but it is possible.

It was over the full line when the tank was full, which alerted me to a potential problem. Possibility of a needle removal is a good point that I actually considered - I just PM'd the member who rebuilt this cluster so maybe can learn if the needle was removed or get some additional perspective. It seems to sweep through the appropriate angle from full to empty it's just shifted clockwise.

[TBONE1964]

Pete,

I sent you a PM. Let me know if you need anything from me.

Take care,
Tom

[DeadheadNM]

PM replied - thanks Tom!

[Mike C]

My Jimmy does almost the same thing. Needle goes to about 4:00 though not all the way to 5:30. It did this once about 10 years ago, then worked fine again for a long time. Starting last fall it once again moved to 4:00. I have not tried to troubleshoot it yet, but my guess is a bad connection at some point. Good luck trying to find your gremlin, I will be watching to see if the same solution can be applied to mine.

[Aruba1]

Originally Posted by DeadheadNM

When I ground that slot on the fuse block I get this - will not go all the way to empty:

Did you ever fix your problem? My tank is full of gas and its at the very same mark as yours.

[leddzepp]

My 68 did the same thing. It was the ground between the wire/sender or sender/tank. With the truck running, and gauge at the 5 o'clock position no matter how much gas was in the tank, I reached back and wiggled the assembly as well as the wire connection. I watched as the needle dropped back quickly to the hatch marks, and slowed down to where it "should" be. Rocked the truck back and forth to slosh the gas and disturb the float. The needle fluctuated a bit and stopped. I topped off the tank and it registered full as it should. Has been working ever since.

[DeadheadNM]

My problem was a bum gauge - dial indicator was off. If your gauge has never been removed start by checking grounds as per Scott and check the fuse to the cluster while your at it. Good luck!

[snipescastle2]

the sender that sits in the tank has a ribbon of fine wire that a copper conductor slides across the ribbon, sometimes varnish/deposits "Insulate" the resistance of the wire, causing the gauge to hang up, just an idea....also, those brass floats will eventually leak fuel past the solder joint where the two halves were joined, causing the float to sink.....
HTH,
Ben