I just installed a new fuel tank and a new sending unit on my 69 Camaro.

I filled the tank and the fuel gauge is reading 3/4, I measured the sending unit resistance and it read 50 ohms which would match the 3/4 reading that I have on the gauge. I confirmed that the tank is really full.

Did you guys had a similar problem? What could be my problem? Do I have a bad sending unit?

Thanks for your Help,
Daniel.

Read the Sticky on this at the top of the page.

Here's another fuel gauge diagnostic that should be a "sticky"; I posted this one a couple of years ago, but Fred changed his home page recently - here's the new URL:

http://chevelleengineer.home.comcast.net/fuelgage.htm


:beers:

ask and you will recieve. stuck.

Thanks for the responses guys.

My sending unit resistance reading (50 ohms) is in line with the gauge reading (approx. 3/4 of a tank).

My question is did you even install a new sending unit that gave you false reading (i.e. defective new sending unit giving 3/4 when tank is really full)?

Thanks, Daniel.

Yes, I have read about guys who bought brand new sending units that were defective out of the box. The best thing to do is test the sending unit out before installing it in the tank. It will save a lot of time and headaches that way.

Hi Guys,

I installed a new Repro 3/8 Single Line Sending unit (second one). It tested Ok out of the box (90 ohms in the full position and 0 when all the way down).

I installed it and put 5 gallons of fuel in the tank, the console fuel gauge was reading around 1/4. When I started the engine, the gauge went down to empty. I filled the tank and the reading was between 3/4 and full (reading 67 ohms).

This is the second sending unit. What could be the problem. Before my old sending unit died it worked fine for years.

What could be my problem?

Thanks, Daniel.

major long shot, but you might check you system voltage with a digital voltmeter while the engine is running. I once had a bad ground to my regulator, without a ground, voltage was at 18 instead of 14. This could conciebably throw off these type of guages.

Good point Jim, I measured my voltage and I have a steady 14.9 VDC.

You have an original been in the car forever 38 year old guage right?
If it was good yesterday, it's probably good today, but...

If you go to radio shack and pick up a 0- 100 ohm potentiometer, you can wire that in place of the sender and check the guage and wiring.

Guage read right, went to zero when you started motor?
Sounds like maybe engine vibration shroting sending unit wire...
Is the wire new, verified in good shape?

Filled the tank, guage went up, but not far enough?
Well that just might rule out the bad sender wire idea.

Does the guage read correctly now with the key on but the motor off?
Is the problem repeatable, or just plain bad now?

Tough one.

If the guage passes the pot test, I'd be tempted to shotgun it with a nother sender, a sender wire, and a new ground wire, from a different supplier.

Is it possible the float is hanging up on something inside the tank?

If you go to radio shack and pick up a 0- 100 ohm potentiometer, you can wire that in place of the sender and check the guage and wiring.
Did that and its fine.


Does the guage read correctly now with the key on but the motor off?
Is the problem repeatable, or just plain bad now?
No, its the same. I even tried disconnecting the wire and to re-connect it with no change. Its constantly between 3/4 and Full.


If the guage passes the pot test, I'd be tempted to shotgun it with a nother sender, a sender wire, and a new ground wire, from a different supplier.
Both sending units were Repros from Classic Industries and both were made by dii Corvex.

Did anybody else used one of these Repro?


Is it possible the float is hanging up on something inside the tank?
It doesn't have anything to hang to, the sending unit is on the edge in the back of the tank (front of the car) while the float is pointing toward the front of the tank (back of the car).

It seems like if the Sending Unit was permanently damages after I started the car !!! I really strange.


Did anyone used one of these 3/8" single line sending unit from Classic Inductries (P/N W566 or 6428845 from the new catalogue)?
If so, does it work fine and is it indicating full when the tank is full?

Thanks, Daniel.

is the arm on it bent wrong and even if the tank is full of gas the arm may not be allowing it to show full because it's bent and can't come up all the way?

If the arm reaches full (full mechanical limit) of the sending unit before the tank is full it will show over full. If it's not reaching the full mechanical limit due to some defect I could see it not showing full.I would try pulling the tank and blocking it with wood on the ground and remove the sender. Get a jumper wire for the ground and sender. Remove the sending unit lock and pull it from the tank. Attach a little fishing line to the float rod and drop it back in the tank. Hook up the wires and see what it reads if it's the same then pull the line to see if the reading goes up. If it does then the problem is the arm not reaching full mechanical limit to show full.

I played with my old sending unit and got it to work using this method and rebending the arm that someone had most likely messed with before.

Good luck
Joe