Fuel tank sending unit ohms?

[erik325i]

Does anybody know how many ohms the e30 fuel tank sending unit is? I need to order an Autometer gauge, but don't know which one to get because I don't know how many ohms the sending unit is. If anybody could be of any help, that would be great.

Erik

[atomic]

I would assume since there are two different size e30 fuel tanks that there would be different readings depending on which fuel tank you have. There is a 12 and 16 gallon tank and I know there are different fuel gauges for these but am unaware if the sending units are different and what the ohms would be. Maybe someone else will chime in with more detail...

[erik325i]

The car in question is an 89 m3. Not sure what size fuel tank it has as I haven't filled it up with gas yet.

Erik

[Justin B]

ohh yeah good luck with that Erik. I went through the same thing a few months ago figuring out the resistance and for what gauge I should use, how, etc, to put together my 2002 gauge cluster with an Autometer gauge set. I don't think our sending units match up directly with any aftermarket gauge's perfectly. I had to employ the advice of some electronics know it alls to help me figure out a basic current limiting circuit.

I am using one sender instead of two, and out of a 318is, but still. Same story. I'll see if I can dig up any information anyway...

[Justin B]

While I'm still looking for it, if you want to find out the difficult way, you could always unbolt the passenger side sending unit, let it drain then measure it when its upside down and right side up then x2 since there's two sending units on the tank. They have to be the same otherwise it'll read differently when it goes around turns. That wont help you much though to figure out how to make it work though.

[ROOR]

So you can't buy an Autometer Speedo/Tach, Oil pressure/Oil Temp, Water temp and fuel level and just plug them in?

[Justin B]

Well, you could, and it all would take wiring to do. Of course they all wont just plug straight into whatever wiring is there for the original cluster. The tank one though is the hardest since the sending units have a different operating range than what the gauge wants to see. You just need to shift it, but for mine it was easy enough that it needed to move the same amount in the same direction at the top and the bottom of the range. I can't find the thread on the forum where I thought I posted all my questions with all the information I had about the senders. Maybe my project thread has something...

[Justin B]

Alright, well I'll look later. But I bought an autometer #1403 kit with the fuel sender being of the 240-33ohm variety, but I only used one in tank sender so my little fix-circuit would need a tweak for twice resistance through the sender. If you look at http://www.r3vlimited.com/board/showthread.php?t=97960 start at post 55, and you'll at least see what I'm talking about.

[erik325i]

Thanks for all the info Justin. I was hoping it wouldn't be too complicated as I'm no electrical engineer. I'll have to see if I can figure something out.
I ended up reading your whole project thread while I was at it. Keep up the good work. I'll probably be making a project thread for my m3 build soon. Mine's nearing its completion finally.

Erik