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aftermarket fuel gauge problems
https://slantsix.org/forum/viewtopic.php?t=29327		 Page 1 of 1
Author:  THOR [ Thu Jun 05, 2008 10:29 am ]
Post subject:  aftermarket fuel gauge problems
I went down to Carquest and ordered part number 81449, which is designed I guess to work with the chrysler sending unit that we use. According to the instructions, it reads anything from 73 ohms, to 10 ohms, which is about where we run.

Mine isnt reading correctly.

When I installed it first, it was reading below empty, which upon inspection of the gas tank, I was pretty much out of fuel. So I drove down to the gas station and put almost 5 gallons in it, and the gauge didnt really move. Except when it was twitching back and forth, but for the most part just stayed around empty. I was thinking it just needed calibration. I got back home, and put almost 10 more gallons in the tank, and it reads higher but still less than 1/4 tank, and it twitches pretty much all the time.

Ceej mentioned that it might be because the factory gauge was still hooked up, but I disconnected the fuel gauge from the dash today, and it made no difference on the level that the gauge showed. The little clamp that grounds the sending unit has been cleaned and the tube itself has been cleaned, so I know the sending unit is grounded.

When I put a multimeter to the line coming from the sending unit, I get around 75 ohms full, and 12 empty, which means that the sending unit is operating like it should be. I have a clean 12V going to the gauge, and a clean ground going to the gauge as well. I have a jumper wire going from the purplish wire on to the signal input on the gauge.

It has been reported to me that this gauge works just great, but I seem to have trouble with pretty much every gauge I try.

For reference, I also tried using a early 90s Dodge Dakota fuel gauge, and it did the same thing, it just didnt move as much as this gauge does. It seems that when would I hook up a gauge to the system, the resistance reading went haywire. So, I am at a loss at what could cause this problem.

~The Other Rob~
Author:  66aCUDA [ Thu Jun 05, 2008 11:25 am ]
Post subject: 
Rob
Make sure you have a really good ground from the tank to the chasis of your car. It can really get funky if the ground is shaky.
Frank
Author:  THOR [ Thu Jun 05, 2008 3:34 pm ]
Post subject: 
Ceej and I took care of the ground, so we know its clean and making good contact. In fact it was his idea to check it in the first place.

~The Other Rob~
Author:  65Dodge100 [ Fri Jun 06, 2008 2:13 am ]
Post subject: 
How did you check the sending unit? An Ohm meter doesn’t always tell us everything that we need to know. If there is a weak connection, it may be connected well enough for an ohm meter to tell you that it’s okay when it actually isn’t. When you send real current through the same weak connection, it could break down and not be able to carry the amps necessary to work the gauge. (Then you hit a bump and it does, then you blink hard and it doesn’t)

If you remove the wire from the tank sender and touch it to a clean ground on the frame, the fuel gauge should go to full. That would rule out the fuel gauge and wiring leaving the sending unit or it’s ground as the problem.

Danny
Author:  THOR [ Mon Jun 09, 2008 3:18 am ]
Post subject: 
I have grounded that circuit and the gauge is dead. I visited a post about the voltage limiter on these units and how they go out... causing a non working fuel and temp gauge. I dont really have the time to fiddle with getting a new one installed, hence the aftermarket gauge.

As far as I know, there isnt much current flowing through the sending unit wire, seeing as how its no thicker than 16 gauge. To make sure that the wire itself wasnt bad, I hooked a jumper lead directly to the fuel sending unit, and measured it, and the ohms came out the same, and upon testing resistance in the wire, I am getting a negligeable amount of resistance from it. And by negligeable I mean, it reads the same as when I make contact directly between the leads on the meter.

I then hooked that directly to the purpleish connector, and still nothing on the gauge, and the resistance doesnt change. If I shake the car with the meter hooked up, the resistance does fluctuate and eventually settle right back where it was before I shook the car, so I know that the sending unit isnt just frozen in the "empty" position.

I am going to pull my spare sending unit, and play around with it, to see if there isnt something else going on, and maybe try running an extra ground strap between the sending unit and the chassis.


~The Other Rob~
Author:  RDJ [ Mon Jun 09, 2008 9:09 am ]
Post subject: 
A while ago, I got a cheap Equus gauge so I could get an idea of my fuel tank contents. It is pretty accurate. When I finally got around to replacing all my gauges with the panel Sick6 made me, I got autometer. The autometer fuel gauge wasn't accurate at all (yes it was supposed to be the 73/10). I didn't try figure out the problem, I just sent it back and used the cheap Equus gauge (saved some money on that also).

don't know if this helps you or not, but with the same sender and theoretically the same ohms rated gauges, I got totally different readings.
Author:  THOR [ Wed Jun 11, 2008 8:53 pm ]
Post subject: 
Alrighty, well I admit that I am infact wrong... at least at this point. I pulled my spare sending unit, and the gauge works perfectly with that.

I snatched a spare battery, my gauge and some jumper wires.

Positive to gauge, negative to sending unit chassis, gauge negative clamped to negative on sneding unit chassis.

Sending unit lead to resistance output on sneding unit. BAM! works almost flawlessly. I did some adjustments to make it read all the way full to all the way empty, and so now its good to go.

I tried the same trick on my sending unit.... got nothing.

Sending unit is bad.

So when I burn up some gas out of the FULL TANK I JUST BOUGHT :roll:
I'll pull the sending unit and swap it out.

and yes, I got the gasket out of my spare tank with the sending unit in it without damaging it. So if I need a gasket when I pull the one in my Dart, I have a spare.

~The Other Rob~
Author:  Jopapa [ Wed Jun 11, 2008 9:59 pm ]
Post subject: 
Quote:
...
So when I burn up some gas out of the FULL TANK I JUST BOUGHT :roll:
I'll pull the sending unit and swap it out....
I think when I eventually get a new tank I'm going to have a bung and drain plug welded in place for just such occasions, before I first fill it up...
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