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Old March 6th, 2004, 12:24 PM
law law is offline
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Join Date: Feb 2004
Location: Louisville KY
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When I fill up the gas tank on my truck, the gauge reads full and continues to read full for many miles (100 or 150 miles). After many miles, the gauge begins to slowly drop as additional miles are driven. If it drive it to 1/2 tank according to the gauge, I had better get gas because my tank is empty at this point. I know, I have run out with the gauge still reading 1/2 tank.

How can I tell where the problem lies?
Old March 6th, 2004, 08:09 PM
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Barrman Barrman is offline
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Are you putting back in the tank capacity of I think 28 gallons? I ask because a few weeks ago, I thought I had run mine dry. My gauge doesn't work and I wanted to pull the tank to mess with the sending unit and clean out some of the crud. I have a fuel psi gauge on mine. The truck stopped running and the gauge read 0 from the electric fuel pump. Thankfully I was in my driveway. I pulled the drain plug from the bottom of the tank. I was going to flush out some of the junk on the drive way. I poured in a gallon and nothing came out. I stuck a screwdriver in the drain hole. Gas came out real fast. I ended up filling every gas can I own and still lost a bunch. I estimate that I drained over 13 gallons out.

I went ahead and pulled the tank. I blew air through the pick up tube and replaced the rubber hose between the tank and the frame mounted fuel line. I had great fuel pressure with only a gallon or so of clean fuel. I haven't had any more problems, but before you blame your gauge, check the numbers.

If it is a gauge error, I would think it is the sending unit. The gauge itself is just an ohm meter. It reads the resistance in the line as made by the sending unit. If the gauge works at all, normally it will work at all readings. Check the online manuals or do an old post search for the resistance values for the M715. Then use an ohm meter hooked to the sending unit lead to see if the gauge is seing what it is supposed to for the given fuel level.
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Old March 7th, 2004, 06:06 AM
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brute4c brute4c is offline
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The stock ohm scale is 0-30 ohms...I wonder too if you have a difernt unit with the wrong scale....
The vent hose on the filler neck...mine did that when I first bought careful when you filler up not to get any in there...mine stopped on the side of the road and when we opened the cap it breeeeeeaaaaaathed in deeply...tryin to suck the tank flat from the vacuum..
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Old March 10th, 2004, 07:52 PM
the1968jeepthing the1968jeepthing is offline
Join Date: Jan 2004
Location: New Hampshire
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mine does that too, its an aftermarket sending unit with a stock scale gauge. i am too poor/cheap to buy the correct gauge so i just messed around by putting resistors in series with the sending unit wire... its still not perfect but its better. i didnt have time to mess around with it too much. the way i see it as long as i know when the tank is empty who cares?


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