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Post by Charlie on Jan 29, 2019 19:05:14 GMT -5
Last week, I was cruising down the highway with about a quarter tank of gas. At 11 mpg, I'm already thinking about where I'm going to stop to get gas. I glance down at the gauges again and notice the fuel gauge pegged out on FULL as if by magic!
It's my assumption that the wire between the sender and the dashboard has grounded out somewhere along the way causing the "full" reading at the gauge.
I was wondering if there's a common problem spot where unneeded grounds take place?
The Temp and Oil gauges both read as they should. |
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DynoDave
CO-ADMINISTRATOR
Motown Mopar-Wizard
Posts: 11,148
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Post by DynoDave on Jan 29, 2019 20:42:10 GMT -5
I think these get their ground via a small metal strap with barbed ends that bridges the rubber hose between the metal lines. It's just a thin piece of raw, uncoated stamped steel, and they do rot away.
I realize this is the opposite of what you are asking, but thought it was worth mentioning.
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Post by odzking on Jan 30, 2019 14:57:28 GMT -5
That is a possibility but i would agree with Dave, I'd bet it's under the car at the sender.
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Post by Charlie on Feb 15, 2019 13:24:53 GMT -5
I found the little strap you mentioned. I moved it around and didn't notice any change. HOWEVER, I did unplug the lead from the sender and noticed the gauge wouldn't give a reading. When I plugged it back in, the gauge pegged out on full again. So it seems there's no unwanted ground along the way of the wiring and the issue would instead be with the sender.
I have a couple of choices of tests I could perform. Old senders all work with the same principle... a contact swipes a coil of wire acting as a resistor. I've got a working Ford sender from my F100 that I could connect to the Charger's wire and ground the sender to the frame and see what kind of movement I get as I move the sender around. While the resistance of the various senders might not be exactly the same, I'm sure they should be close enough to make the gauge move around a bit. IF it turns out I can make the gauge move, then that will confirm that I need to change the sender in the tank.
Being that I work on vintage electronics, I have a huge supply of various resistors and could pick out a few between 5 to 60 ohms and tie them to the sender lead and see what kind of reading it gives. Again, would likely confirm the sender is bad.
Oddly... while driving today, I noticed the gauge dropped to 3/4 and then went back to full again.
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Post by Charlie on Feb 15, 2019 15:18:12 GMT -5
Looks like something is indeed funky with the sender. I placed a 10 ohm resistor between the sender wire and ground and got a reading of 3/4 tank on the gauge. I then swapped out the 10 ohm resistor for a 47 ohm.... got a reading of 1/4 tank on the gauge.
I then put an ohm meter between the sender post and ground... I got 1 ohm... which would explain it pegging all the way to the right. I'm pretty sure a full tank reading should be in the neighborhood of 5 or 6 ohms.
This is a bit backwards from typical sender failures. I suspect I'll be able to remove the sender and be able to repair it instead of replace. I just filled up yesterday, so i'll have to wait till I run most of the gas out and lower the tank. I will be anxious to see what's causing this.
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Post by Nacho-RT74 on Feb 15, 2019 20:25:26 GMT -5
resistance on Mopars are 10 +/-2 ohms for full and 70 +/-5 ohms for empty. This consist on a point mounted on a brass L shaped tab attached to float arm running along a coil/rheostat conected to the terminal outside the fuel sender unit. My guess is simply, the point is making contact with chassis into the assembly, or tab is bent reaching the end of rheostat
sometimes is fixable, sometimes not. Being there Done that
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Post by Charlie on Feb 15, 2019 21:16:32 GMT -5
Well I hope I can straighten it out without having to buy a new one. I see they're about 100 bucks at O'Reilly's. I see there's two to choose from... one with what they're calling a "fuel return" connection and one without. Mine would be the without choice.
Looking at the connection area of my current sender, parts look pretty shiny... so I'm guessing it's been replaced in recent times.
I didn't study it too much, but, it kinda looks like I might be able to remove the sender without removing the tank. I'd have to lower the exhaust pipe on that side. Seems that might be easier than lowering the tank. I'll get a closer look at that tomorrow.
I disassembled, cleaned, soldered, and re-assembled the sender in one of my Fords. Worked out pretty good... which was a huge plus being that they don't make the sender for the AUX tank on a 77 Supercab. Hopefully I will have the same luck with the Charger.
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Post by Nacho-RT74 on Feb 15, 2019 22:30:26 GMT -5
can be found on $40-60 rate, Brass float and metalic strip between rheostat and terminal ouside sender, like originally was. Just with straight outled, and original was angled. I got it on ebay from Vans.
I had to weak it a bit to get a better reading but works nice.
( no need to remove the tank, just get the tank less than half full )
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Post by Nacho-RT74 on Feb 15, 2019 22:35:27 GMT -5
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Post by Charlie on Feb 15, 2019 22:51:27 GMT -5
Roger that! Thanks!
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