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Unread 10-13-2013, 08:22 PM   #1
danimal45
Registered User
1989 YJ Wrangler 
 
Join Date: Oct 2012
Location: Longmont, CO
Posts: 4
Fuel Gauge Question need help

This is for a 1989 YJ 2.5 with 15 gal tank fuel injected.

My gas gauge had never worked since I bought the jeep. I always assumed that it was the sender unit but was not that worried about it. Well last month my fuel pump died. I went through the usual test everything first and finally decided to pull the tank. I bench tested the pump and no worky. Now since I had the whole thing out and apart I cleaned the sender unit and it had a smooth 1 ohm empty to 88 ohm full just as it is supposed to. So I plugged it back in and ran the float up and down. The gauge still pegs high and flutters around a little, but does not read even remotely correct.

I measured the voltage (tan wire to ground) and it only reads 7.8 to 8.1 volts DC at the supply to the unit. I am thinking that this is supposed to be 12v and there is a fault either in the gauge or intermittent wire fault somewhere.

Can someone with a working gas gauge pull the plug at their fuel pump and verify the voltage at the pump connector for the sender unit?

Anyone else have a similar problem?

Thanks in advance.

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Unread 10-14-2013, 11:51 AM   #2
Que89YJ
Web Wheeler
1989 YJ Wrangler 
 
Join Date: Apr 2008
Location: Detroit, Michigan
Posts: 15,707
I think you are measuring the voltage wrong. Recheck your voltage with the sending unit unplugged. You have the ground that is common a supply for the fuel pump power and the fuel guage line. With the resistance of the sending unit you will see less then 12 volts but if you read across the plug to ground you should see the 12 vdc.
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Unread 10-15-2013, 02:57 PM   #3
danimal45
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1989 YJ Wrangler 
 
Join Date: Oct 2012
Location: Longmont, CO
Posts: 4
Quote:
Originally Posted by Que89YJ View Post
I think you are measuring the voltage wrong. Recheck your voltage with the sending unit unplugged. You have the ground that is common a supply for the fuel pump power and the fuel guage line. With the resistance of the sending unit you will see less then 12 volts but if you read across the plug to ground you should see the 12 vdc.
I read the Ohm resistance value of the sender unit itself and it tested to spec. I am measuring actual supply voltage from the source (tan wire) to ground (black wire) at the plug with the sending unit unplugged and I get 7.8V DC. There must be something wrong with the gauge then. Thanks for the reply.
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Unread 10-15-2013, 03:07 PM   #4
danimal45
Registered User
1989 YJ Wrangler 
 
Join Date: Oct 2012
Location: Longmont, CO
Posts: 4
Here are the drawings, any other ideas?



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Unread 10-16-2013, 12:46 PM   #5
Que89YJ
Web Wheeler
1989 YJ Wrangler 
 
Join Date: Apr 2008
Location: Detroit, Michigan
Posts: 15,707
The guage reading full is a good place to start. Short the fuel level sending unit wire to ground at the tank connector by using a pin and a short piece of wire. The guage should go to empty. If it does then the issue is in the tank area. If it doesnt post back and we can go from there.
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