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Discussion Starter #1
I know, I know but this is not just another gas gauge post. I did a search of all of the postings for this BEFORE I pulled the tank today to fix my gas gauge but it still won't work.

I thought this was going to be simple but that's not how it goes with these problems.

This is what I have done so far:

* Checked the tank sender (tan wire)with the ohm meter and got 45 ohm even with a full tank so I suspected the sender.

* Cleaned and secured the ground wire.

* Just to make sure I checked the gauge with resistors to see if the gauge would read above 1/2 tank - it did so it looks like the sender.

* I pulled the tank, replaced the sender. I checked the old sender and it worked thru the full range !

Reassembled everything and filled the tank, gauge only goes to where it was before - 1/2 tank.

I checked the tan wire from the tank and only go to 45 ohms again with the NEW sender ! I checked the ground again and the same thing - 45 ohms.

The only thing I can think of is the float on the sender looks like it might hit the fill tube where it come all the way back in the tank. Other than that I am ay a loss to figure this one out

Any ideas are welcome !
 

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This is my first reply so I hope I can help.
You measured 45 ohms on the ground circuit? That's a lot. Ideally I would look for .5 ohm or less. Sounds like a bad ground.
 

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i have hever had the sender out of a car...
so this may be incorrect. but on a heavy vechicle the float is a empty cylnder attached to a arm and it should float
at the top of the gas.the trucks a lot of
times will leak diesel in to the float
or some times it is a sponge like float
and if the seal on the float goes it will
not read correctly
 

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Team5150,

What year of car do you have??????


Do you have the wrong sender????
The 1964 model year units use a 0-45 ohm internal resistance.

1965-1972 use 0-90 ohm internal resistance.

Let's get back to basics

Unplug the tan sender wire that comes from the trunk harness from the sender output wire. Turn the ignition switch to "ON" position. Needle on the gas gauge should go way above "FULL". Now take the tan wire (the one that leads into the trunk wiring harness) and ground it to a CLEAN bare metal surface. HOLD THE WIRE THERE, an assistant should read the gas gauge. It should be pointing to "EMPTY". If it passes these tests, the gauge is GOOD!! Sender issues should then be focused on.
 

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Discussion Starter #6
Coppertop, thanks ! I already tested the gauge that way you explained and used some 22 ohm resistors to see if it would register in the in between areas and it worked fine.

With a NEW sender installed it reads the same as the old sender did. I checked the old sender when I took it out and it was fine worked all the way thru the range.

As I said it is like something is keeping the float from going up in the tank. When I had it out I looked and it seemed like the fill tube was right next to the gauge sender in the tank.

Thanks !

Tom
 

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Haven't seen something like you are describing. Assuming both the old sender and new one both are functional, perhaps your idea that the sender is being stopped by something may be something to think about. The fill tube can't move. It's brazed into the tank. Only thing that comes to mind is perhaps someone slid an anti-siphon device into the fill tube. These were popular add-ons in the 70s along with locking gas caps. The thing slid down over time and its interfering float movement. Still I can't really see something like that just sitting at the end of the tube unless it hung up on something. Not a great thought but the best I've come up with.
Maybe try:
Running the car until the gage starts moving.
Re-measure the sender. If it was originally stopped it should now read just below 45 ohms. This will show float movement downward both mechanically and by resistance.
Sounds a little backwards but now re-fill the tank. Should take about 9 gallons at this point.
If this works out it should give you a good idea that the new sender is working but hitting something.
 

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Discussion Starter #8
Thanks for the input John !

This has really got me stumped. I can't be the only one this has happened to ! I thought maybe someone installed a different tank in this car, but the car is in very nice condition so that's not likely.


The old sender would show 45 - 48 ohms when full and after a 1/2 tank it would register normally.

I am thinking of just running it dry again, pulling the tank and bending the float around to the other side.

I might try attaching a string on the float handle, putting it back in the tank and try pulling it up to the top while checking the ohm reading and see if it hits anything.

I have to burn off a tank of gas before I can do that. Humm, that should only take a couple of days with 3:73's going back and forth to work !

Tom
 
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