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| | | | Joined: Mar 2001 Posts: 279 Shop Shark | | Shop Shark Joined: Mar 2001 Posts: 279 | I've checked all of the posts, but I can't seem to find one that fits the problem I'm having, so here goes. This is a '72 GMC pickup. When the tank is full, the gauge reads 1/4-tank. It drops as the fuel level goes down, so it functions that far at least. I replaced the fuel sending unit. Same issue with the new one. Only goes to 1/4 tank when the tank is full. If I disconnect the wire to the sending unit, the gauge goes to full. Reconnected the gauge goes back to 1/4 tank on a full tank. I added a ground strap from the fuel tank to the frame. Didn't change anything. I pulled the ground from the battery and cleaned that terminal connection. No change. I tried raising the arm on the sending unit with the wire connected and the unit grounded. If I raise it all the way up, the gauge goes to about 1/2 tank and that's all. I'm guessing at this point that it has to be the gauge. Since this is a '72, I'm not sure how the gauge is wired. It may be a circuit board (I can't see the back side of the gauges from under the dash). Any suggestions anyone? Any help would be appreciated. Thanks. | | | | | Joined: Jul 2005 Posts: 308 'Bolter | | 'Bolter Joined: Jul 2005 Posts: 308 | My bet would be the sending unit, I am not sure what they cost for a 72 but they usualy are not that much to replace.
Ed | | | | | Joined: Mar 2006 Posts: 1,703 Shop Shark | | Shop Shark Joined: Mar 2006 Posts: 1,703 | as Ed stated ..
did you check to make sure it isnt STUCK? | | | | | Joined: Mar 2006 Posts: 1,703 Shop Shark | | Shop Shark Joined: Mar 2006 Posts: 1,703 | | | | | | Joined: Mar 2001 Posts: 279 Shop Shark | | Shop Shark Joined: Mar 2001 Posts: 279 | The float is not stuck and the sending unit is fine. It is brand new and functions properly. As I said, raising the arm all the way up (which would be higher than a full tank of gas) only brings the gauge to the 1/2 tank level. | | | | | Joined: Aug 2005 Posts: 6,377 Ex Hall Monitor | | Ex Hall Monitor Joined: Aug 2005 Posts: 6,377 | One would assume a new sending unit is working OK. The best way to check is to check the resistance using a multi-meter. I don't know if 72 still used the 30 ohm sending unit/gauge set up or not. A check of your shop manual should tell you that. Assuming 30 ohms is correct and using 30 ohms as an example, if the sending unit reads 30 ohms with the float in the "full" position, the gauge should read full. If it doesn't and all connections and grounds are good the gauge would be at fault.
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| | | | | Joined: Mar 2005 Posts: 1,029 Member | | Member Joined: Mar 2005 Posts: 1,029 | You may not have a good ground to the case of the fuel gauge. I believe that would cause the symptoms you exhibit. | | |
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