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-   -   Sending Unit Not Working ???? (http://www.hotrodders.com/forum/sending-unit-not-working-146426.html)

cashflow55 10-11-2008 09:58 AM

Sending Unit Not Working ????
 
Guys, need help. I have a standard Stewart Warner fuel guage and that seems to be working properly after a resistance test. I have removed my sending unit from the tank and made sure the ground was connected from the frame to the sending unit and the sending unit wire was connected to the fuel gauge. Fuel gauge is grounded and powered. Checked sending wire from rear to front with meter and it is good. When I move the sending unit float up and down, nothing happens on the gauge. The gauge goes directly to past full when wired and key to switched to on. Any thoughts?? Thanks

pepi 10-11-2008 11:08 AM

two thoughts
Is the sending unit a SW? if so can you read a change in resistance as you move the float, if any of these has a NO answer ................. replace the sending unit

DENCOUCH 10-11-2008 11:46 AM

Fuel gauge issue.
 
Quote:

Originally Posted by cashflow55
Guys, need help. I have a standard Stewart Warner fuel guage and that seems to be working properly after a resistance test. I have removed my sending unit from the tank and made sure the ground was connected from the frame to the sending unit and the sending unit wire was connected to the fuel gauge. Fuel gauge is grounded and powered. Checked sending wire from rear to front with meter and it is good. When I move the sending unit float up and down, nothing happens on the gauge. The gauge goes directly to past full when wired and key to switched to on. Any thoughts?? Thanks

Don't feel bad, Girls need help too. :D

"I have a standard Stewart-Warner guage (sic) that seems to be working properly after a resistance test". You are speaking in a weak voice here as if unsure if the gauge is okay or not. Unsure if the gauge is okay or not, are we? As you know, there are just a few components that make up this system.

Disconnect all the wiring to the sender and check it out using an Ohms test. Only two terminals on the sender unit, so set your meter to Ohms and moving the float up and down, you should note a change in the signal from 0 ohms to around 90 ohms if it is a GM product. That means the sender is going it's job. Reinstall the sender and leave the sender wire & ground wire disconnected for next test.

Turn on the ignition key to the "On position", set your meter to DC voltage and with one probe on the sender wire & the other to the ground wire on the frame, measure the voltage. You have 12v or better, then good.

If you are showing less voltage, bypass the ground wire and look for another place to check for a better ground. Even if you have to run a dedicated ground from the battery for testing purposes, find a ground that will allow you to eliminate the present ground wire as the culprit. Just because it is bolted to the frame does not mean it is a good enough ground!

This is why we are using a meter instead of our eyes to test this.

If you have now rediscovered a good solid 12v after bypassing the present wire grounded to the frame, repair the bad ground cable connection and verify that the ground is good by repeating the 12v test between your new ground and the sender wire. (sometimes the frame may need additional grounding from the battery to get this voltage).

After these tests, we have verified;

1. sending unit is operational and ohms out 0 to 90 ohms during operation.
2. 12v between ground and sender wires at sender connections. (means wiring path to sending unit is good, both 12v and ground).

At this point, and because your gauge goes to full when the key is switched to the on position, I would check the ground wire to the gauge for proper ground. I would take a test lead and wire to the ground side of the battery and see if that did the trick.

If nothing, then I would scrap the gauge. If you had a variable resister with the value of 0 to 150 ohms, you could wire it to the gauge and check the operation of the gauge that way if you wanted to nail it down completely, but at this point, I would toss the gauge if your current sender checked out okay.

cashflow55 10-11-2008 03:42 PM

Still Here
 
Thanks for the reply. I have confirmed the sending unit is working and has a reading of 0 to 30 ohms. I have confirmed my old SW gauge is for 30 to 240 ohms or so. Therefore, I have purchased a new fuel gauge that is rated for 0 to 30 ohms. The problem is I still cannot get a reading on the new gauge. The hot to the gauge is confirmed and I confirmed the ground on the gauge by connecting the ground clip from a light tester to the ground on the gauge and it did light up when touched to the hot on the gauge. I assume that confirms it is grounded properly. Also, I have confirmed the gound on the sending unit is to the chassis and working in the same manner. I wired the sending wire (new wire outside the car) straight to the sending terminal on the gauge. What do you think I am missing here. Thanks so much for the help.

DENCOUCH 10-11-2008 05:48 PM

getting close
 
It honestly at this point looks as if it is a grounding issue.

You have almost gotten all the parts out and on the ground at this point, the only thing you have left to try is hooking a wire up and grounding the gauge directly to the sending unit (bypassing the frame connections) and running this connection to the battery ground.

At this point, you have already dedicated wiring from the gauge to the sending unit, no?

Grounding directly is the only part left to try.

note: good form in grabbing the gauge that matches the sending unit.

See pix for wiring.
http://i185.photobucket.com/albums/x...nds/wiring.jpg

cashflow55 10-11-2008 07:04 PM

Sending Unit Issue Continues
 
Thanks again. If anyone could help once last time it would be greatly appreciated. Here is where I am. Sending unit verified 0 to 30. New fuel gauge verified 0 to 30. Sending guage working on ohms meter 0 to 30. Used power wire straight from battery to new gauge and ground wire straight from battery to new gauge to rule out the this and thats. Sending unit is sending out 0 to 30 ohms thru the sending wire, verified with the meter. Here is what happens. When all is wired and the power is connected, the gauge reads basically full. When the sending unit float arm is moved, the gauge moves slightly up towards the full mark or just past, but the movement is very slight. I don't get it. If the sending unit is working on 0 to 30 ohms verified at the guage wire, why is the new verified 0 to 30 ohms guage not responding correctly. Thank you in advance for any help, I need it.

cashflow55 10-11-2008 07:14 PM

It Works - Sending Unit
 
To all my appologies. I did not take enough time to look at the wiring diagram sent by DENCOUCH. After making sure the gound was in line from the battery to the gauge and sending unit, all works as it should. Thanks to all for the help. This web site is the best.

DENCOUCH 10-11-2008 07:56 PM

Quote:

Originally Posted by cashflow55
To all my appologies. I did not take enough time to look at the wiring diagram sent by DENCOUCH. After making sure the gound was in line from the battery to the gauge and sending unit, all works as it should. Thanks to all for the help. This web site is the best.

We ALL love stories with happy endings! :thumbup:

Have fun.


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