How to check fuel guage??

[locab36]

Just picked up a 84 Chevy short wide box. Inline 6 replaced w/305, factory turbo 350. Fuel guage isn't working. Driving it home reading under half tank and stopped to put in some gas. After filling 2 gallons the tank was full and the guage didn't move. Took the dash guages out and checked the pink wire from the sending unit, it shows a little over 90 Ohms on my multimeter. I have 12V+ on one side of the printed circuit and the input from the sender but there is a third (ground?) and I don't know what it is. If I take the guage out How can I check it?

Thanks

John

[Stingray42]

mines gone to hell too... dif problem (mien read waaaay fulll... like 3oclock position) but this may help me out too (and i may be able to find something for ya too) thanks

[longhorn71]

ttt.my blazer reads 1/4 tank when it is dry.

[72 CustomCamper]

Originally Posted by Stingray42

mines gone to hell too... dif problem (mien read waaaay fulll... like 3oclock position) but this may help me out too (and i may be able to find something for ya too) thanks

Usually when the gauge is at the 3oclock position, it means it has a bad ground. My neighbor has the samp problem on his I think we tracked it down to the fuel tank selector switch for the dual tanks. Hope that helps...


Chuck

[Stingray42]

Originally Posted by 72 CustomCamper

Usually when the gauge is at the 3oclock position, it means it has a bad ground. My neighbor has the samp problem on his I think we tracked it down to the fuel tank selector switch for the dual tanks. Hope that helps...


Chuck

i think this may get kinda confusing with three of us with problems... but here goes!

i had duals tanks and one was removed by the PO. now the guage did work, but with the needle at the wrong spots (half was empty, etc) then it stopped working, then i cut out the selector valve underneath the truck, now it still doesnt work. can someone give the volt reading that the guages should be putting out at full, empty, etc? also, where should you pick up power to check grounds, etc? ( i think this will help all three of us track down soem problems) Thanks!

[Russell]

I heard somewhere that the little ceramic plate on the back can get corroded or whatever and cause the gauge to display inaccurately. Maybe pull it off, clean it up / shoot it with some contact cleaner?

Here is a picture of what I am talking about, the white peice with the blue center:

[72 CustomCamper]

Originally Posted by locab36

Just picked up a 84 Chevy short wide box. Inline 6 replaced w/305, factory turbo 350. Fuel guage isn't working. Driving it home reading under half tank and stopped to put in some gas. After filling 2 gallons the tank was full and the guage didn't move. Took the dash guages out and checked the pink wire from the sending unit, it shows a little over 90 Ohms on my multimeter. I have 12V+ on one side of the printed circuit and the input from the sender but there is a third (ground?) and I don't know what it is. If I take the guage out How can I check it?

Thanks

John

On the gauge it's self you shoould have 12v coming in from the pinkw/ black stripe wire. Then a signle going to the sending unit. The 3rd wire is the gauge ground...


Chuck

[784X4GUY]

Yeap mine is real weird it sometimes reads right then sometimes it acts like it is sticking. Im trying to figure this out to so if anybody else has some info, I would appreciate it...Thanks Mike

[NeCrOmAnCeR]

When measured like you said "90 Ohms from sender" the guage should read full. The GM senders in our trucks measure 90 Ohms when the tank is full, and 0 Ohms when empty. You are on the right track, reinstall the guage and remove the wire from the sender and ground it to the frame with the ignition on and check to see that the guage reads empty. You then know that the guage is OK. Because of the realitively low resistance used in our trucks, any corrosion or loose/dirty grounds will cause the guages to read inaccurately. Thus the "3 o'clock" reading usually indicates a bad ground on the fuel tank/sender unit causing high resistance.

The guage itself has a +12v lead, a ground, and the wire to the sender. Also check to make sure that the sheetmetal "nuts" on the back of the guage are makeing good contact with the resistor block (white porcelin) on the back as the guage uses this resistor for calibration.

It is also possible the sender itself is dirty/faulty and causing the reading to jump around. But check the connections first.

[784X4GUY]

I've also heard that tank selector valve can cause all kinds of problems. I have a fuel flow problem and Im thinking its because the selector valve is stuck in the middle. Im gonna have to replace that someday...Later Mike

[locab36]

I believe I've found the culprit. I went to local junk yard for another guage. They didn't have the exact one I needed (70's model ). I installed the older guage and it seems to work. I just didn't have the hole for the brake light. After looking at the guage I removed I decided to replace that little resisitor on the back and give it a try. That seems to have done it. Guage reads overfull ( 94 Ohms ) but I believe its accurate. When I was checking to see if it was the guage or sender I checked voltage back through the pink to the sender and was reading 3.4 v. Thats when I knew it was bleeding voltage back through the guage. Hopefully its fixed.

Thanks for the help.
John

[Stingray42]

ok.... so if a have a bad ground, how would i go about fixing it? (3 o'clock position) does it require something in the dash or under the truck?

thanks again

[Stingray42]

ttt....thanks

[PhilaTruck]

quoted from necromancer:

... Because of the relatively low resistance used in our trucks, any corrosion or loose/dirty grounds will cause the gauges to read inaccurately. Thus the "3 o'clock" reading usually indicates a bad ground on the fuel tank/sender unit causing high resistance.

The gauge itself has a +12v lead, a ground, and the wire to the sender. Also check to make sure that the sheetmetal "nuts" on the back of the guage are making good contact with the resistor block (white porcelin) on the back as the guage uses this resistor for calibration. (end quote)

This is a great post. I've always had trouble with my fuel gauge. Although nothing that a good thump with the middle finger wouldn't fix. Figured mine was either the gauge or the dash connection. As long as I have at least one of my middle fingers, I'm not really worried about it.

Good luck & let us know how you make out.

-Todd

[magnethead]

our dually will read 1/8 tank when empty...but as long as we know that, i say who cares.

[76bonanza]

Hey chuck on that friend of yours truck did you just replace the switch in the cab? And how did you get it out. Mine is doing the 3 oclock thing and I think it is the switch because If I flip it back and forth a few times it corrects it self.