Can you adjust sending units and gas gauge readings?

[Rokcrln]

Just what is says, is their a way to adjust the reading of a gas gauge when you change to a different tank? I have put a late 80's Blazer tank in Low Buck and now I find out the reading is way off. What can be done about this, is their a way of adding resisters or somthing to fix this? Or is their some kind of an adjustable in line box to fix the problem? I know alot of people use different tanks so what have you done to fix the problem?

Thanks for any info!

Kevin
LFD Inc.

[jamis]

Can you be a little more specific.
What gauge are you using?

Mean while check the conductivity of the circuit with and ohm meter, since the gauge works reading resistance any resistance added other then the sending unit will affect your reading. With the wire off the sending unit, check the ohm reading at the gauge by placing one end of the meter on the terminal and the other on ground. Place back the wire on the sending unit, remove the wire that leads into the gauge and then check the ohm reading there. They should be very close.

There are many other things that can cause a bad reading such as component compatibility or a bad component. You may have to remove the sending unit and check its range of resistance. Also check that the sending unit is neither too short nor too long. the total length of the sending unit with the float all the way down should be a little short of the depth of the tank.

With the gauge out reconnect the wires and add a ground and check the readings at the gauge as you move the float threw its range. And tell us what its doing. If its a little off you can bend the float arm to get it closer.

[Rokcrln]

The gauge is a stock 67-72 gas gauge and the tank is out of an 89 Blazer. I will have the bed off today and I will check the resistance, float depth and motion as well as the gauge reading when done manualy. I am fairly sure it is a compatibility issue and that is why I am wondering if their is an adjustable "box" to calibrate it with, but I will check your other susgestions as well.
Thanks for your help.

Kevin
LFD Inc.

[3/4tonterror]

you can move the needle, it pulls off the guage. then put it where you want it. just be carefull there aluminum and bend easy.i removed mine when i painted them

[Rokcrln]

I guess I should have added that it seems the ratio is off from full to empty not so much just the placement of the needle if that makes any sence.

Kevin
LFD Inc.

[jamis]

I think the standard for GM is 0-90 ohm for the gauge and sending unit. 0 being full and 90 empty. But I don’t know if that applies to 80s blazer or 70s truck. Maybe some one can check a new 70s factory sending unit and see if that is true ,then check the one you have.

As far as accuracy goes you have to take that with the grain of salt. They where never meant to be very accurate, and they only get worse with age.

[Rokcrln]

I have both the 70 tank and the 89 tank but I do not know how to check the sending unit for OHMs! I know they are never p[erfect but at 1/2 a tank of gass the gauge shows full and when full it reads way past full!

Kevin
LFD Inc.

[jamis]

I would be happy to help with some instruction and pictures. Do you have a digital OHM meter or can you borrow one?

[Zeke]

with sender removed from tank use a multimeter set to ohms with one lead connected to sender wire and other to ground (metal part of sending unit) move the float and read meter. with full being 0 ohms it would seem your gage needle is off since you can't get any lower than zero=full. if you had something other than 0-90 the gage would never show full. I am not sure if the 0 ohms is the full reading since if you disconnect the sending wire, infinite ohms, it reads way past full

[Rokcrln]

I do have a digi meter and I am headed out now to pull the bed so in about an hour I will be back with info!

Kevin
LFD Inc.

[jamis]

Originally Posted by Zeke

I am not sure if the 0 ohms is the full reading since if you disconnect the sending wire, infinite ohms, it reads way past full

0 ohms would be a perfectly closed circuit with no residence (sender wire completing the ground circuit threw the variable resister in this case). If you disconnect the wire it goes to empty, meaning an infinitely open circuit not the 0 ohms but its infinite opposite.

[charlie diaz]

Im not trying to sound like a smart-ass here, but if you said that the gauge reads 1/2 full when it is empty, then with the tank empty, cant you just pull the needle off the guage and press it back on at the empty line? Then it will read right at empty. It shouldn't really matter where the needle is at when you have a full tank, right? I mean the real intent of a fuel gauge is just to let you know when youre about to run out of gas. Definitely keep us posted though. I'm about to undergo the same swap, and I was wondering what to do about the sending unit.

[Rokcrln]

Well it is my sending unit. The Ohm's reading was all over the place so I hooked it back up and manualy moved it thru it's range and it read fine unless you wiggled the unit at all then it would peg way past full or bounce off empty. In calling around for a new one (no luck, 4days out ) A guy told me they have had a problem that the cali gas tends to eat the contacts and causes eratic or no readings.

Kevin
LFD Inc.

[jamis]

Glad you found the problem. a new one shouldn't cost too much.

[Rokcrln]

Originally Posted by jamis

Glad you found the problem. a new one shouldn't cost too much.

$77.00

Not that bad but more than I wanted to spend. But then again I don't want to carry a jerry can or run out of gas.

Kevin
LFD Inc.

[lbpd719]

and in the end if you need some "fine tuning" adjustment, you can put a potentiometer in line with the sender, down side there is if someone messes with it, it will be a mother to get it back where you want it..

Good luck..