I got gas...

[mullinax95]

.... gauge blues!

Sorry tech question!


I got my new Autometer MCX series gas gauge installed and of course it isn't reading correctly with the amount of fuel in the tank. The gauge comes with a sending unit but it is the type that needs to be installed vertically. The sending unit reads 248 ohm empty and 31 ohm full. In the instructions it states that the gauge has to have a 240-33 ohm sender. Now with my stock sending unit I have 12 ohm full and 8.95 volts with the key on. I have not checked the ohms with it empty.

I first started with a empty fuel tank and seeing what the gauge read connected to the stock sending unit (worked fine with stock gauge). The Autometer gauge read between 1/2 and 3/4 with the tank empty. I tried to install resistors and got the needle right on the empty but when I filled up the tank today it only goes up to 1/4 of a tank. I new it was a long shot with the resistors but I didn't know what else to do.

The entire car has been freshly rewired with a EZ wiring fuse box and wiring.

Where do I need to go from here?
Do I have a short somewhere with almost 9v on the sending unit wire?

Help!

 

[doktor_x]

I've been scrounging for a solution that doesn't involve chopping a hole in the top of your tank (that would suck) and haven't found anything off-the-shelf. Looks like it may come down to swapping/grafting the variable resistor and float from the Autometer 3262 to the existing sending unit/pickup tube. I suppose that it could be done without too much torment once you matched the sweep of the new float to the size of the tank, but it's still a bit Macgyver-ish. I'll poke around a bit more. It seems like Autometer would've considered this orientation.

 

[mullinax95]

I've been scrounging for a solution that doesn't involve chopping a hole in the top of your tank (that would suck) and haven't found anything off-the-shelf. Looks like it may come down to swapping/grafting the variable resistor and float from the Autometer 3262 to the existing sending unit/pickup tube. I suppose that it could be done without too much torment once you matched the sweep of the new float to the size of the tank, but it's still a bit Macgyver-ish. I'll poke around a bit more. It seems like Autometer would've considered this orientation.

I've been scrounging also .LOL!

I don't understand why the resistor trick isn't working. It would seem that it would but it doesn't work for some reason. Last night I cut the wires and removed the resistors. Jumped the wire coming from the gauge to ground and it went straight to FULL so the gauge and wiring seem healthy. It's just the fact of the sender isn't correct. If I can get it in the ball park I will be happy.

 

[RedFish]

resistors can change the end points respectively but not the range of resistance. Incase that dont make sense, consider a 36" wide window going in a wall. Move the window left or right all you want and its still 36" wide.
The range is determined buy the length of nichrome resistance wire used in the circuit. One sender may have 6 inches of wire wound on a 2 inch radius while the other has 3 feet of wire wound on a 4 inch radius.
You'll just about have to combine the 2 senders (if it can be done).
I'm willing to study the designs and possibilties but no guarentees.
Best looking group of gauges I've seen for the rallye panel so lets not give up.

 

[mullinax95]

resistors can change the end points respectively but not the range of resistance. Incase that dont make sense, consider a 36" wide window going in a wall. Move the window left or right all you want and its still 36" wide.
The range is determined buy the length of nichrome resistance wire used in the circuit. One sender may have 6 inches of wire wound on a 2 inch radius while the other has 3 feet of wire wound on a 4 inch radius.
You'll just about have to combine the 2 senders (if it can be done).
I'm willing to study the designs and possibilties but no guarentees.
Best looking group of gauges I've seen for the rallye panel so lets not give up.

I see what you are saying. I'll have to pull the tank most likely to get the fuel gauge dead on. Figure something out. I've been wanting to pull the tank and have it boiled out at a radiator shop, install a true 3/8 sending unit, etc.. so I guess that will be the fix. More $$$$ LOL!