Help With Testing Sending Unit and Fuel Guage
Thread Starter
Pro
Joined: Nov 2004
Posts: 585
Likes: 0
From: Royal Oak MI
Help With Testing Sending Unit and Fuel Guage
OK guys can anyone run through testing the sending unit and fuel guage.
I followed a couple threads about testing the sending unit, and lifting the arm up through 90 ohms at the full up position, but where do I attach the tester points on the sending unit. I was trying numerious pspots and was not getting a reading.
Second, battery, tank and sending unit are out of car, and guage is still reading 1/4 tank. Saw something about attaching ground to frame and sending unit should go to full, for this to happen does battery need to be in? I also assume the ground is the flat wire and not the one with the boot on it. Is there also some other test using the sending unit wires?
Please help I would like to make sure sender is OK before I buy a new one.
Thanks
I followed a couple threads about testing the sending unit, and lifting the arm up through 90 ohms at the full up position, but where do I attach the tester points on the sending unit. I was trying numerious pspots and was not getting a reading.
Second, battery, tank and sending unit are out of car, and guage is still reading 1/4 tank. Saw something about attaching ground to frame and sending unit should go to full, for this to happen does battery need to be in? I also assume the ground is the flat wire and not the one with the boot on it. Is there also some other test using the sending unit wires?
Please help I would like to make sure sender is OK before I buy a new one.
Thanks
Le Mans Master
Joined: Jun 2002
Posts: 8,339
Likes: 24
From: I can walk to MA
So, you have some sort of Ohm meter - like a DVM ?
You connect one lead to the steel base of the sending unit -
where it meets the tank. The other lead connects to the
little screw terminal that the wire attaches to.
The threaded terminal goes through an insulator and then
connects to the flat wire (inside the tank). The flat wire then
connects to the potentiometer (the metal can thingy).
If you get infinite or open circuit, then the fine resistance wire
inside the little metal can may be broken. Raising the lever
should move through the range of 0-90 Ohms.
I'm not sure about the guage issues. I would assume the
battery needs to be installed for that to move. With the battery in,
you could test the guage by grounding the sending wire - yes.
You know, I tested mine, and it was kind of erratic - not smoothly changing values.
I didn't want to take a chance. I just saw that ZIPs got them on a group purchase sale - $70.
I just ordered one.
http://www.zip-products.com/Corvette...ml/68-82GP.asp
You connect one lead to the steel base of the sending unit -
where it meets the tank. The other lead connects to the
little screw terminal that the wire attaches to.
The threaded terminal goes through an insulator and then
connects to the flat wire (inside the tank). The flat wire then
connects to the potentiometer (the metal can thingy).
If you get infinite or open circuit, then the fine resistance wire
inside the little metal can may be broken. Raising the lever
should move through the range of 0-90 Ohms.
I'm not sure about the guage issues. I would assume the
battery needs to be installed for that to move. With the battery in,
you could test the guage by grounding the sending wire - yes.
You know, I tested mine, and it was kind of erratic - not smoothly changing values.
I didn't want to take a chance. I just saw that ZIPs got them on a group purchase sale - $70.
I just ordered one.
http://www.zip-products.com/Corvette...ml/68-82GP.asp
Last edited by NHvette; Apr 1, 2005 at 10:06 PM.
Thread Starter
Pro
Joined: Nov 2004
Posts: 585
Likes: 0
From: Royal Oak MI
NH
Thanks, I tested it like you said and if I go from the bottom screw its really eratic like you said yours was, if I test from on top(or on the inside where the flat wire is) its a little more uniform and goes up over 100 Ohms. Would you think the insulator that the threaded terminal attaches to is bad?
I thought the sending unit was a good price at ZIP for $70 as well so I orderd the sending unit when I bought the adjustable strut rods that are also on the group purchase, but I got the strut rods and no sending unit, I called and they said the SU was on back order so I canceled the SU.
Thanks, I tested it like you said and if I go from the bottom screw its really eratic like you said yours was, if I test from on top(or on the inside where the flat wire is) its a little more uniform and goes up over 100 Ohms. Would you think the insulator that the threaded terminal attaches to is bad?
I thought the sending unit was a good price at ZIP for $70 as well so I orderd the sending unit when I bought the adjustable strut rods that are also on the group purchase, but I got the strut rods and no sending unit, I called and they said the SU was on back order so I canceled the SU.
Le Mans Master
Joined: Jun 2002
Posts: 8,339
Likes: 24
From: I can walk to MA
Mine shipped the next day.
On your sender, the screw terminal end is brass I think. It may
be oxidized enough to give bad readings. Try cleaning it up with
some steel wool or scotchbrite and try again. It sounds like
yours might be OK.
No - I don't think it's likely to be a problem with the insulator.
Usually crap getting into the potentiometer and giving high readings.
That or the little resistance wire inside gets broken.
Look in here - you should be able to see what I mean.
I have it apart, but don't have a picture of the insides.
You can see the springy metal wiper in the picture here.
This rubs along a strip of insulator that has tiny wire wrapped
around in a spiral. How long a piece of wire it contacts -
determines the resistance.
You can bend back the metal tabs and get it apart to clean, but
be warned .. It is very fragile inside.
On your sender, the screw terminal end is brass I think. It may
be oxidized enough to give bad readings. Try cleaning it up with
some steel wool or scotchbrite and try again. It sounds like
yours might be OK.
No - I don't think it's likely to be a problem with the insulator.
Usually crap getting into the potentiometer and giving high readings.
That or the little resistance wire inside gets broken.
Look in here - you should be able to see what I mean.
I have it apart, but don't have a picture of the insides.
You can see the springy metal wiper in the picture here.
This rubs along a strip of insulator that has tiny wire wrapped
around in a spiral. How long a piece of wire it contacts -
determines the resistance.
You can bend back the metal tabs and get it apart to clean, but
be warned .. It is very fragile inside.
Last edited by NHvette; Apr 2, 2005 at 12:26 AM.
