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Old 08-08-2012, 06:21 PM   #1 (permalink)
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fuel sending unit ohms

Im swapping a 93 12v cummins into a 79 ford. I want to use the stock dodge tank. From my research it shows me that a 79 ford reads 10 ohms full and 80 ohms empty. The 93 dodge sender reads 10 ohms full and 73 ohms empty. Is that enough difference to cause me to fun out of fuel before the tank shows empty or will it show empty and still have a couple gallons in it?
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Old 08-08-2012, 07:45 PM   #2 (permalink)
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You'll run out of fuel before you hit empty.
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Old 08-08-2012, 11:08 PM   #3 (permalink)
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Well, I think the 78-91 Ford trucks and vans use 10 to 130 ohm, but, the real question is will the Dodge tank sending unit work with your gauge.

The Ford's IVR sends a 5v (+) pulse to the fuel tank sending unit (probably orange wire in the main rear harness). Will that work successfully and safely with your Dodge sending unit? If not, you might be better off using a universal unit from Summit in the Dodge tank designed for a Ford gauge.

Is the tank still in the Dodge so you can test it or do you know the voltage requirements, if any, for the Dodge gauges and sending unit ?

Even being diesel, be a shame to send 5v (+) to the tank if it was not expecting it.

All things being equal, you can just bend the arm with the float, to adjust it to the different setting, just like you do with a universal sender.

Finding our what your current tank uses is pretty simply. Run it towards empty, unplug the connector at the bumper, run jumpers and read with a DMM. At the same time, relocate and reground the ground itself, after this many years it is probably not that great and flaky, so it will not give you a true OHM reading.

Last edited by 4x4prepper; 08-08-2012 at 11:09 PM.
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Old 08-09-2012, 09:25 AM   #4 (permalink)
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Quote:
Originally Posted by crazyredneckanyhow View Post
Im swapping a 93 12v cummins into a 79 ford. I want to use the stock dodge tank. From my research it shows me that a 79 ford reads 10 ohms full and 80 ohms empty. The 93 dodge sender reads 10 ohms full and 73 ohms empty. Is that enough difference to cause me to fun out of fuel before the tank shows empty or will it show empty and still have a couple gallons in it?
You could just solder a 10 ohm resistor to the dodge sending unit. It wont ever read full, but at empty there will be a little reserve.

Why not use the Ford tank? Turn one of the evap ports into a return, and swap in a larger filler neck.
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Old 08-10-2012, 04:01 AM   #5 (permalink)
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The ohms readings i got were from the book at napa. Thats what they listed for both tanks. I may just buy an auto meter gauge and run that.

As far as using a stock ford tank goes it would cause problems. The stock tanks are galvanized. When diesel fuel gets any sort of water in it the sulfur turns to basically culfuric acid which will erode the galvanize off the tank and start to clog up the fuel system. Ive been told this by a few people and also read it on cummins forum. I just figured since i had the stock plastic dodge tank i would go ahead and use it.
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Old 08-10-2012, 04:46 AM   #6 (permalink)
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You are correct on the zinc coating. I forgot that part.

You can reseal the Ford tank to make it compatible, or use a poly tank.
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Old 08-10-2012, 05:38 PM   #7 (permalink)
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hook the dodge tank up when empty and make note what the gauge reads
then dont let the tank get even close to it unless you like to bleed your injectors
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