FUEL Gauge

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FEATHERDUSTER76

FEATHERDUSTER76

The Feather Duster is Mopar's Light Weight
Joined
Sep 18, 2021
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YAKIMA WA.
My fuel gauge wasn't working so at the ground on the fuel tank
i cleaned the area now if I fill the tank when I start
my Duster the gauge needle will get to about 3/4 drop back to around 1/2 and stay there as I drive it drops to MT but
i can still go 100 mile b4 I run out. Is it gauge ground or what LOST
 
I’d say your ground is still weak or the gauge is on its way out. Especially if it worked before?

it’s a 10-73 ohm gauge so you can manually test it at full, empty and interpolate anywhere in between if you remove the gauge and have an ohm meter…
 
I did test to see if the voltage limiter is working. test light between sending unit and wire to gauge and light pulsed like suppose to. I'll check the ground
 
Said this many times. You must treat this as an end to end system, and there is many pitfalls along the way. It's like a chain, any weak link or broken link, it won't work right

Is the cluster getting power and by that I mean CORRECT power IE correct voltage right to the limiter?

Is the limiter actually working properly, IE have you checked the other gauges?

The way to start with these gauges is to use the KNOWN test resistors, and see if the gauges work correctly, here:

c-3826-jpg.jpg
 
Sounds like a cracked or partial sunk float to me. Generally the tank gets a pretty good ground simply from being bolted into place and the grounding clip from sender spigot to fuel line does squat. Take an ohm meter and put the leads from the car body to the face of the sender unit. Should read zero, after you see that it's not a ground issue. Take the sender wire off the sending unit and short it to ground BRIEFLY, fuel gauge should go full scale.
 
I would dispute the claim that the tank grounds effectively through the frame. There is insulating packing between the tank and the trunk floor. The only contact would be through the strap which is only potentially grounded at each end. Many cars are undercoated in this location, and otherwise it is a likely area for rust. Plus there is a rubber gasket where the sender meets the tank — the contact there is just through the tightening ring, which touches at 4 points and is also generally rusty. In my experience, if you remove the ground strap the gauge stops working, period.

I think you might be right about the float, however.
 
mvh said:
I would dispute the claim that the tank grounds effectively through the frame. There is insulating packing between the tank and the trunk floor. The only contact would be through the strap which is only potentially grounded at each end. Many cars are undercoated in this location, and otherwise it is a likely area for rust. Plus there is a rubber gasket where the sender meets the tank — the contact there is just through the tightening ring, which touches at 4 points and is also generally rusty. In my experience, if you remove the ground strap the gauge stops working, period.

I think you might be right about the float, however.
Click to expand...
The sending unit is grounded by a small strap that attaches to the fuel line, and the output line of the sending unit.

IMG_4281.jpeg
 
FEATHERDUSTER76 said:
I did test to see if the voltage limiter is working. test light between sending unit and wire to gauge and light pulsed like suppose to. I'll check the ground
Click to expand...
volt meter and ohm meter are two different things.

refer to the chart two posted above for the desired values.

dadsbee knows what he’s talking about too so that may well be a cause
 
Last edited:
FEATHERDUSTER76 said:
my Duster the gauge needle will get to about 3/4 drop back to around 1/2 and stay there as I drive it drops to MT but
i can still go 100 mile b4 I run out. Is it gauge ground or what LOST
Click to expand...

The gauge going to 3/4 then to 1/2 ( IMHO) rules out leaky float. If float was filling it would not empty itself then start refilling

The IVR (if mechanical and the RT Engineering unit) has a warm up period where 12 volts is fed to the guages for a few seconds. This gets the needle moving pretty fast, then it starts it's on off dance to regulate the voltage to the 5 to 6 volts square wave needed by the gauges.

What you might be seeing is the initial warm up period of the IVR.

As for the empty and still have 100 miles on the tank ( not a bad thing!)

My guess is there is exsess resistance in the path from body ground to the sender, to the wire, to the gauge. This extra resistance will fool the gauge into thinking it is lower than it really is.

As mentioned before you need to get some resisters ( 1 watt) in the 10, 23 and 72 ohm range and then go between good body ground and the wire at the sender.

And report back what the gauge does.

Other issues might be:

  1. a failing IVR, sticking closed,
  2. a failing gauge (post a photo of the gauge with the key in the off position)
  3. If you removed the sender you might have messed up the adjustment (at some point between 67 and 76 the design of the sender changed and messing up the adjustment is harder)
  4. And as mentioned be sure you have a good ground from the sender to the car body. A temporary jumper cable will work for testing.
 
OK Thanks to everyone who responded these tests and other things suggested I'm sure will take me several day's so I'll be back with You all with results Thanks again to everyone who responded
 
4mulas said:
I’d say your ground is still weak or the gauge is on its way out. Especially if it worked before?

it’s a 10-73 ohm gauge so you can manually test it at full, empty and interpolate anywhere in between if you remove the gauge and have an ohm meter…
Click to expand...

Supposed to have a mopar clamp that goes from the sending unit exit line to the gas line of the car, completing the ground over the short rubber gas line coupler hose.

☆☆☆☆☆
 
My best guess is this is not a rte or any solid state regulator but just a OEM mechanical limiter. Wild needle swings are a symptom of failing mechanical limiters. I've seen the same needle swing in temp gauges where the panel had only the 2 gauges. The temp needle would swing to max then fall back to correct position at switch on but only after the water was hot. If there was a similar needle swing in the fuel gauge at cold start, I never saw it.
 
4mulas said:
volt meter and ohm meter are two different things.

refer to the chart two posted above for the desired values.

dadsbee knows what he’s talking about too so that may well be a cause
Click to expand...
OK first thanks for all of the response's the ground was good it was the gauge. I ended up pulling the hole dash out glove box cluster radio everything because I had to replace the nylon grommets for the windshield wipers and replacing them all they were bad and already had new temp gauge now with the new gauges (temp and fuel)all is working like it should once again thank You all for your help
 
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