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Tweaking a fuel sending unit

cmayna

cmayna

DILLIGARA?
Donator
The fuel gauge in Red has been reading on the empty side when infact there is fuel in the tank. This has been going on for a year + and I think I might consider fixing it. What is the easiest way to adjust the sending unit to read more accurately?

I was going to run the car until it was reading almost empty which means I actually have about 4 gallons remaining. I would then drain the tank, put back 4 gallons and then tweak the sending unit's arm downward a little until I could get it to read 1/4 of a tank.

Is there another way by using an ohm meter? If so what about laying the sending unit on a piece of paper, marking the limits of travel of the bowl including halfway. Then hook a meter to read the ohms, reading the meter when moving the arm from empty to full. Find the halfway number in ohms. Holding the arm still at halfway and tweak the end of the arm until it lines up with the halfway mark on the paper.

I think I just confused myself on this latter idea.
 
When the tank is full , does the meter say so ?
How quickly ( after how many miles ) starts the needle to sink ?
Craig , you have automeer gauges so Full tank should be around 75 ohms and empty should be around 10 ohms.
When the rod is bent, after several miles the needle of your fuelmeter starts to go down .?
Don't have an old gastank?
But you have a bigger tank , isn't it ?
 
Bruno,
This is in Red not Shag. Red has a stock 16 gal tank. Yes it reads full when the tank is filled, but it seems to drop faster than normal because numerous time when I'm almost on empty, I end up still having 4 gallons in the tank. Thus to me by slightly bending the arm downward just a tad, it would read higher. Thus as I said earlier why not just put 4 gallons in the tank and keep tweaking the arm until it reads quarter full. This might take 3-4 times of installing and removing the sending unit, but "oh well"

Shag has a 20 gallon tank and I might do the same by initially putting in 5 gallons and tweak (if necessary) the arm until it reads 1/4 full.
 
There's two other ways of adjustment that are preferred before bending the sending arm inside the tank.

First, make sure the arm is pointed downwards in the tank. If it is put in sideways, you can have the symptoms you describe.

Secondly, it may need an adjustment of the Constant Voltage Regulator. There's a little trim pot on the back side that you can adjust once you break the epoxy seal. I can't remember which way to rotate it, but here's what I do. I monitor my gas mileage so when I believe I have 4 gallons in the tank, I adjust the pot so that the fuel gauge reads 1/4 full. That gives me an accurate reading of when I need to fill the tank back up. Remember to be careful when removing the dash, and it's best to disconnect the battery as the ammeter lines are hot and not fused. Adjusting the trim pot will also adjust your temperature and oil pressure gauges the same amount, so you'll need to mentally re-adjust your comfort zone for those two gauges as well.
 
Randy and Rick,
Thanks for the replies. I think I'll check out the sending unit on Shag while I'm at it. Randy, if the arm was not pointing down correctly, wouldn't the hose bib be pointing in a wrong direction instead of up towards the fuel line?
 
"cmayna" said:
Randy and Rick,
Thanks for the replies. I think I'll check out the sending unit on Shag while I'm at it. Randy, if the arm was not pointing down correctly, wouldn't the hose bib be pointing in a wrong direction instead of up towards the fuel line?
Click to expand...

I don't remember, but I don't think you can trust the orientation of the hose bib direction relative to the fuel line for proper orientation of the arm in the fuel tank.
 
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