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Can’t Seem to Figure Out Fuel Gauge/Sender Problem
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Author:  74A1Swinger [ Thu Feb 06, 2014 7:25 pm ]
Post subject:  Can’t Seem to Figure Out Fuel Gauge/Sender Problem
I was working on my fuel gauge/sender problem and have done all the testing I can think of and I hope someone might know what it is that I missed.

So, I first had a problem with my fuel gauge reading 1/2 full when the tank was full and empty when the tank was 1/2 full. After testing I found the fuel sending unit rheostat was missing in a few places so I replaced it with a new unit.

While I was replacing the old sender I found that the old gasket was a homemade cork gasket that was twice the thickness of the new replacement and so I had to use the old one until I could find one that was thicker.

Next I checked the gauge reading which now read 7/8 full when the tank was full and would drop down in increments of about 1/8 to1/4 tank each time I stopped and restarted the car. And when it read empty there was half a tank of gas yet.

I tested the gauge by putting a jumper on the gauge side connector and the other to ground and it read full, when removed it was on empty.

Then I checked the ground strap with one end on gauge side connector the other to ground strap connector at the fuel outlet. And the reading was good. I also checked the ground right on the fuel outlet before the ground strap and it was good too.

Now I connected the jumper to the fuel sender terminal from the gauge connector side to test the connector and it read the same as before when the new gauge was first installed. :x

Then I checked the new sender out of the tank and it worked fine. So now I'm out of tests and could use any ideas.

I'm wondering if the mounting flange on the tank is somehow causing the problem because it must be stretched out to make it twice as deep as it's supposed to be, but I don't know. :?

Tell me what you think.

Thanks,
74
Author:  DusterIdiot [ Thu Feb 06, 2014 10:01 pm ]
Post subject:  Calibration...
When you get a new aftermarket sending unit, you have to calibrate it...which means you have to bend the "arm" so when installed it has a ful range of motion...the first Spectre sender I got was bent from the factory in a way that the float rested on the bottom of the tank and would indicate 1/4 tank...(this also meant that anything above 3/4 of a tank read full as the float got buried if the tank was filled to the brim)....

Another thing to look for is the sending unit ground, there is supposed to be a piece of metal with two clips on the ends that go to the metal fuel line coming out of the sending unit, and the other end clips to the metal line running down the body of the car toward the engine...if this isn't there it cna cause some 'intermittent' issues (in a pinch you can use two hose clamps and a piece of wire, or hose clamp a wire to the sending unit then a length of wire to a screw at the frame rail for ground).


Good luck...

-D.Idiot
Author:  Pierre [ Thu Feb 06, 2014 11:41 pm ]
Post subject: 
Assuming there are no electrical issues (loose connections, grounds etc)....

The aftermarket senders have the proper empty and full resistance (73-10 ohms) but the wrong scale. If you bend the arm to get one end right, the rest will likely be off. They (including the mopar branded replacements) seem to have a linear scale where the stock ones weren't. Look at what's left of your stock one - the coils of wire towards the bottom are very closely spaced and as you go up they get wider apart.

Years ago I went through this. After much time and headache I devised my own experiment. I cut a hole in a tall garbage can and taped the sender to it. I marked several graduations along the inside and filled it with water to each graduation then measured the resistance. The original sender had different readings.

If you want your stock gauge to work, you'll have to find a NOS sender. The type where the arm pivot / resistance wire is near the base, not part way down the pipe.

As for the gasket thing - separate issue. If it really needs a double thick gasket I imagine it would be clearly bent out of shape. It may not be the inner flange - the outer tabs could be bent outward. If there's nothing obvious - the locking ring has two steps on it. The ring needs to be turned so the tabs on the tank sit between the steps on the ring. If the tabs only sit on or before the first step, the gasket won't get compressed enough. Sometimes the locking ring is a pain to turn. The right tool makes it boatloads easier. You can get away with sticking a shaft between two opposing tabs and twisting.
Author:  74A1Swinger [ Sun Feb 09, 2014 5:28 pm ]
Post subject:  Re: Calibration...
Quote:
Another thing to look for is the sending unit ground, there is supposed to be a piece of metal with two clips on the ends that go to the metal fuel line coming out of the sending unit, and the other end clips to the metal line running down the body of the car toward the engine...if this isn't there it cna cause some 'intermittent' issues (in a pinch you can use two hose clamps and a piece of wire, or hose clamp a wire to the sending unit then a length of wire to a screw at the frame rail for ground)
This was The first thing I corrected.
Quote:
When you get a new aftermarket sending unit, you have to calibrate it...which means you have to bend the "arm" so when installed it has a ful range of motion...the first Spectre sender I got was bent from the factory in a way that the float rested on the bottom of the tank and would indicate 1/4 tank...(this also meant that anything above 3/4 of a tank read full as the float got buried if the tank was filled to the brim)....
I know I may sound stupid, but that I didn't think of. Thanks for the info I think that's probably the major issue.

74
Author:  74A1Swinger [ Sun Feb 09, 2014 6:11 pm ]
Post subject: 
Pierre,

I had a power outage and lost my almost complete reply. I'm out of time so I'll have to catch you tomorrow. Sorry!

74
Author:  74A1Swinger [ Tue Feb 11, 2014 7:53 pm ]
Post subject: 
Hey Pierre,

Your post is very helpful regarding the linear aspect of the sending unit vs. the original design, so I'll be checking into that closely because I think your right. When I tried to repair the old one I saw exactly what your talking about.

Also on the outer flange ring, I to thought it is pressed out and/or deformed. It's definately not putting the lock ring it self on, I know I got that on all the way and solid.

Well for now I think that will probably give me all I need to get the gauge reading correctly.

Thanks for everyone's great advice,
I'll let you know how it turns out!

74
Author:  74A1Swinger [ Tue Mar 18, 2014 9:43 pm ]
Post subject: 
Well it took some leg work and help from another post I started (about my fuel filler tube), but I think I got it figured out and I'm just waiting on the parts to ship.

So, the problems were:

1) Fuel tank is deformed over all, but mostly the outer ring depth, the flange plate angle which points the sending unit up instead of level so the float can't reach the bottom of the tank or rise all the way to the top.

2)The fuel filler tube was cut in half and welded to the tank (why use a grommet? :roll: ), but it was welded in an extra 5 inches deeper in the tank which doesn't allow the tank to fill all the way up. Along with a rubber hose installed to bridge the gap in the 2 parts of the filler tube making the internal vapor line useless.

And the Spectra Premium sending unit rheostat turned out to be non-linear just as the OEM original.

Can you believe it? :shock:

74
Author:  64ragtop [ Mon Mar 24, 2014 6:15 pm ]
Post subject: 
Sounds like "backwoods engineering" (I hope that's politically correct) at its finest on the filler! Good to know about the non linear Spectra rheostat!
Might be a good thing to stock up on for future replacements.

BC
Author:  '67 Dart 270 [ Tue Mar 25, 2014 1:47 pm ]
Post subject:  Christmas....
OK, this is the really expensive option.

I put the aftermarket fuel gauge and limiter (which works properly with aftermarket sending units without adjustment) on my Christmas list. The thing is, you also have to use their TEMP gauge due to the two gauges feeding off the same limiter.

It's expensive, $60 for CSVR1 limiter and (ugh) $90 each for the CS211 fuel gauge and CS212 TEMP gauge...but my family must love me 'cause they bought the set for me. (I may not get anything next Christmas...). They couldn't figure out why I wanted these so badly...

See: http://www.chargerspecialties.com/gauges.htm

The needles were pink though, so I painted them orange to match the rest of the gauges. You might as well paint the other (faded) needles while you're in there, the paint is only $8...see: http://www.ebay.com/itm/Chrysler-Fluore ... 4897.l4276

My gauges look and work like new.

bg
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