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SMFire History

Fuel gauge troubleshooting

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Hello all-

We are finally getting started back up on our 52 Mack project. After a few false starts and some hiccups we’ve decided to tackle a lot of issues on our own...

Our fuel gauge never comes off Empty. The sender seems to be working as the ohms cycle up and down when moved. The “Fuel” pull knob is frozen so I bypassed that for now and we have 12v going into the fuel gauge. We also have only 1 other wire coming in which I assume is the “S” wire from the sender. When I create a new jump wire from the post on the sender to the post on the gauge nothing happens. Is the gauge grounded by the mounting bolts to the back of the dash? It looks like a nightmare to get any of these gauges out from the back but at this point I think the gauge is bad.

I’m tempted to install a new aftermarket fuel gauge below the dash to see how that goes for now. Anyone know off hand what the ohm range is on the sender?  Hoping to not have to pull the sender again if possible. 

Thanks!

Dom

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Does the sender at the tank have a good ground?  Also is the truck still positive ground? That will make the gauge read off. Gauge is wired different for + and - ground systems.

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Excellent point.

Yes we have a good ground at the sender. I can use it as the ground to test a positive circuit. 

The rig was converted to negative ground before we got it back but the gauge has never worked for us. Do we need to do something to the wiring to the gauge for the negative ground system?

 

 

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I’ve also removed the sending unit again to bench test it. The OHMS are reading and cycling up and down but are not consistent and swing wildly sometimes with the same OHM value at top and bottom.

We will order a new sending unit and matching OHM range aftermarket gauge. Anyone know what the OHM range on the original gauge is so I can keep them all the same when we go back to original?

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Posted (edited)

So the local truck shop is no help with the part but he did suggest I may have a hard time finding the sender as it has the pickup tube built in. 

Anyone have a part # or suggestion on replacement?

Getting a “-200 error” when trying to upload the picture. 

Edited by SMFire History

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Look for a fuel gauge and sender from one of the hot rod suppliers like Jeggs, Summit or Speedway Motors (my first choice). You can put the sender in the tank anywhere you choose same as the gauge. If you clean and fix the rheostat on the original sender the wires should be ok but I may be incorrect. I have fixed "bad" senders by cleaning the contacts on the rheostat area of the sender. They do develop wear spots. 

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Posted (edited)

Thank you for the reply. Everything I’ve found online is a sender only and no pickup tube. Bobs speedometer will refurbish ours but it’s out of our price range for the moment. 

I think i will carefully drill out the rivet caps and see what’s inside. 

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Edited by SMFire History
Bad grammar

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I decided to dig into this and see what was going on inside.  I tried to attach some pictures of the process but for some reason the site is not playing nice.  Here’s what I did:

1. Drilled out 2 small rivets

2. Used a tiny screwdriver to pry the 2 flange pieces apart. They are separated by a rubber gasket.

3. Used some pliers to bend the fuel tube retaining tabs so it was free.

4. Removed sending unit piece from the fuel tube piece  

The contact on the sender is worn and has a hole in it. I may see if my local alternator shop has anything that I can use to replace it. 

EEEA0FE4-3574-4420-A4BB-98446A59A245.thumb.jpeg.0a3b2db8ef2b3d83818cacfe26e0c8d1.jpeg

 

The other area area inside the top flange that houses the fuel pipe and rheostat that Chevy mentioned seem worn.

 

9E47A3F7-3B37-4857-8651-640BACC981A8.thumb.jpeg.16c734e1242c973404df38163bcf1b85.jpeg

 

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I did try to clean them up a bit and it helped but not much.  This would make sense why the readings are all over the place.  It seems like the ohm range is 480-30 but I don’t see much on the web for senders in that range.

Any suggestions on where to get parts? (Insert laugh here).

I have not had much luck finding any senders with pickup tubes... maybe one with a built in fuel pump?

 

 

 

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