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Username Post: Fuel Gage on my 1968 C10 Doesn't Work        (Topic#95992)
68C10LB 
Member
Posts: 11

Loc: NY
Reg: 03-28-05
03-29-05 03:13 PM - Post#661646    

The fuel gage on my 1968 C10 doesn't work. Using the "dip stick method" it appears that I have about 1/3 of a tank of gas. I tried checking the continuity between the sending unit and the fuse panel and the wire is good. I took a voltage reading between the sending unit post and ground and it reads about 0.5 volts. However, since I don't know what the voltage should read at the sending unit . . .. I don't know if that is good or not. I know that the sending units have a reputation for failing, but before I order a new sending unit I would like to isolate the problem.

Any ideas on how to troubleshoot the gage/sending unit?
Would it damage anything if I removed the wire from the sending unit and connected it to +12VDC? Or would that be a good way to test the fuel gage.
Is there an expected OHM range that I can use to test the sending unit?

Also, the Chevy book calls out a special tool for accessing the sending unit, is that really required?

 
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JimKshortstep4x4 
Chevytalk Moderator & "10th Year" Silver Supporting Member
Posts: 4559
JimKshortstep4x4
Loc: Muskegon, MI, USA
Reg: 03-28-02
Re: Fuel Gage on my 1968 C10 Doesn't Work
03-29-05 03:31 PM - Post#661647    
    In response to 68C10LB

The tank sending unit sends a signal to the dash unit from 0 to 90 ohms. 0 ohms is empty, 90 ohms is full. The reading is linear so 1/3 of a tank should read 30 ohms on the sending unit. The sending unit in effect grounds the dash gauge using a rheostat that is calibrated to the gauge.

A quick check is to ground the sending unit wire and the gauge should go to empty. Disconnecting the wire should cause the gauge to read past full.

Removing the sending unit can be done using a screw driver and hammer and gently tapping the screw driver to turn the locking ring so it can be removed. A non sparking screw driver is recommended. The sending unit can be removed with the seat slid forward.

Jim
Member 65-66 Full Size Chevrolet Club

65 Impala SS, 400sbc, Muncie M-22
66 Impala SS, 396, TH 400
69 El Camino, 350, TH 350
71 Short bed stepside 4x4, 350/TH 350
71 Snow plow, 4x4, 350, TH 350
72 GMC Shortbed, stepside, 427/TH 400


 
68C10LB 
Member
Posts: 11

Loc: NY
Reg: 03-28-05
Re: Fuel Gage on my 1968 C10 Doesn't Work
03-29-05 05:00 PM - Post#661648    
    In response to JimKshortstep4x4

Jim:

Thanks again!! I ran the tests you suggested and when I disconnected the sending unit the gauge went up past full (just as you said it should). Then I took a resistance reading on the disconnected sending unit and it only read about 5 ohms. I'm going to add a new sending unit to my order.

Thanks again for your help

 
JimKshortstep4x4 
Chevytalk Moderator & "10th Year" Silver Supporting Member
Posts: 4559
JimKshortstep4x4
Loc: Muskegon, MI, USA
Reg: 03-28-02
Re: Fuel Gage on my 1968 C10 Doesn't Work
03-30-05 03:03 AM - Post#661649    
    In response to 68C10LB

Sometimes the floats will leak and sink causing a low reading.

Sounds like you have isolated your problem though.

Jim
Member 65-66 Full Size Chevrolet Club

65 Impala SS, 400sbc, Muncie M-22
66 Impala SS, 396, TH 400
69 El Camino, 350, TH 350
71 Short bed stepside 4x4, 350/TH 350
71 Snow plow, 4x4, 350, TH 350
72 GMC Shortbed, stepside, 427/TH 400


 
Rob Smith 
Senior Member
Posts: 197

Loc: Illinois
Reg: 02-22-05
Re: Fuel Gage on my 1968 C10 Doesn't Work
03-30-05 03:19 AM - Post#661650    
    In response to JimKshortstep4x4

Don't forget to add a new tank o-ring to your list of parts also! The PO replaced the float on my truck and reinstalled it with the flattened out old o-ring. The tank would leak at anything over 3/4. The o-ring is about a buck!

Rob
1968 K20 4x4 Fleetside "Bertha Butt" One of the Butt sisters!


 
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