Fuel Guage not working

[Andrew Ryan]

I have a 68 Chrysler 300. I replaced the fuel tank a few years ago along with the sending unit at the same time. The fuel guage stopped working at that time, i assumed it was the fuel sending unit and replaced it again. My guage is still not working. I find nothing in my factory service manual about this circuit. Suggestions of where to start would be greatly appreciated.

 

[MoparJimNE]

Maybe an obvious question, and going by memory - did you re-install a good ground strap jumper from the sending unit, across the rubber fuel line, to the metal fuel line? the gauge won't work without a good ground strap connection...

 

[Big_John]

Try this to check the sender. Gas Gauge Sender Flow Chart

 

[57fury440]

You can use a piece of wire and some small fuel line clamps to hook one up. You can order an original from a few of the suppliers.

 

[Andrew Ryan]

Maybe an obvious question, and going by memory - did you re-install a good ground strap jumper from the sending unit, across the rubber fuel line, to the metal fuel line? the gauge won't work without a good ground strap connection...

I believe i did but i have to get under and confirm that. It would be awesome if that were the issue. Simple fix.

 

[CBODY67]

Some people might perceive the factory clamp as "funny looking" until they realize it has a special purpose of grounding the tank so the gauge works.

Enjoy!
CBODY67

 

[SPF Required]

That missing ground strap was my issue when I had the tank replaced. Hope it is an easy fix for you too.

 

[mrs49]

I have a 68 Chrysler 300. I replaced the fuel tank a few years ago along with the sending unit at the same time. The fuel guage stopped working at that time, i assumed it was the fuel sending unit and replaced it again. My guage is still not working. I find nothing in my factory service manual about this circuit. Suggestions of where to start would be greatly appreciated.

Check voltage going to the sending unit while you are under the car.

 

[Andrew Ryan]

Check voltage going to the sending unit while you are under the car.

Thanks!

 

[darth_linux]

You should be getting a 5v pulse every few seconds to your sending unit.

 

[Andrew Ryan]

Thank you for the specs!

You should be getting a 5v pulse every few seconds to your sending unit

 

[Andrew Ryan]

Thank you for the specs!

I am getting voltage to the sending unit

 

[Andrew Ryan]

Maybe an obvious question, and going by memory - did you re-install a good ground strap jumper from the sending unit, across the rubber fuel line, to the metal fuel line? the gauge won't work without a good ground strap connection...

There was no ground strap so I fashioned one with bare wire and hose clamps above and below the rubber fuel line, grounding the metal line. I still have no guage. An observation….. for a while, the fuel guage, upon turning the the ignition on, would would shoot up past the full mark to the right. Now the guage just sits at empty. I wonder if the fact i wasn’t grounded for so long, fried the guage. The manual refers to a “tester C-3826" to perform all of the testing functions of the sending unit, the low fuel relay and the guage “. Something i dont have and i didn't see any on ebay for sale. How would i test the guage without the suggested chrysler tester C-3826?

 

[darth_linux]

I pulled my sending unit and manually moved the arm around to see how it registers. Upon startup my fuel gauge briefly goes to the “true” level and then sinks to about half of that value. Every so often it doesn’t work at all. I think the gauges are just not real reliable.

 

[Sport Fury 67]

Look at this video - Dead Dodge Garage

 

[thethee]

There was no ground strap so I fashioned one with bare wire and hose clamps above and below the rubber fuel line, grounding the metal line. I still have no guage. An observation….. for a while, the fuel guage, upon turning the the ignition on, would would shoot up past the full mark to the right. Now the guage just sits at empty. I wonder if the fact i wasn’t grounded for so long, fried the guage. The manual refers to a “tester C-3826" to perform all of the testing functions of the sending unit, the low fuel relay and the guage “. Something i dont have and i didn't see any on ebay for sale. How would i test the guage without the suggested chrysler tester C-3826?

This sounds like you've accidentally grounded the sending unit wire directly, effectively bypassing the sending unit. Even with a full tank the sending unit has ~10 ohms iirc so in bypassing that the gauge gets too much power and fries.

If you're no longer seeing any movement of the fuel gauge you're probably going to need a replacement.

 

[Andrew Ryan]

This sounds like you've accidentally grounded the sending unit wire directly, effectively bypassing the sending unit. Even with a full tank the sending unit has ~10 ohms iirc so in bypassing that the gauge gets too much power and fries.

If you're no longer seeing any movement of the fuel gauge you're probably going to need a replacement.

When you say "grounded the sending unit wire directly" what i did was only what the original ground clip would do which is to ground the metal fuel line to the other side of the rubber fuel hose, metal fuel line. Its not connected or grounded to the frame of the car. Ill check the guage cluster for 5 v to see if the regulator is working. If it is, then im with you in thinking my guage is bad.

 

[57fury440]

I think he is saying that you might have grounded the wire that goes from the sending unit on the tank to the gauge. A quick test to see if the gauge is working is to have the ignition key to on and momentarily ground the wire from the gauge. If nothing happens then either the wire is disconnected, or the gauge is bad. If the gauge is working, it should start to read towards full. If it was grounded for too long, it would burn out the gauge.

 

[Andrew Ryan]

I think he is saying that you might have grounded the wire that goes from the sending unit on the tank to the gauge. A quick test to see if the gauge is working is to have the ignition key to on and momentarily ground the wire from the gauge. If nothing happens then either the wire is disconnected, or the gauge is bad. If the gauge is working, it should start to read towards full. If it was grounded for too long, it would burn out the gauge.

Thanks. I haven’t grounded the sending unit but someone else shared temorarily grounding to see if the guage reads anything at all, which ill try. Everyone’s been very helpful. Looking forward to not having to break out the gas can when i run out of fuel!

 

[thethee]

I think he is saying that you might have grounded the wire that goes from the sending unit on the tank to the gauge. A quick test to see if the gauge is working is to have the ignition key to on and momentarily ground the wire from the gauge. If nothing happens then either the wire is disconnected, or the gauge is bad. If the gauge is working, it should start to read towards full. If it was grounded for too long, it would burn out the gauge.

^^This

If there is a short in the sending unit wire to ground it will burn out the gauge I think.

But I'd recommend following the flow chart mentioned by @Big_John in post #3 for further diagnosis.