Programmable fuel gauge - is there an easier way to do this using resistor?

Picked up an autometer cobalt programmable fuel level gauge for the e30.

e30 uses a 0-60 Ohm (full/empty) sender.

The gauge is pre-programmed for a GM sender (0-90 Ohms).

There is a process to do a "custom setup" but that involves setting the empty with an actual empty fuel tank, and then filling the entire tank and setting the full reading. Since I don't happen to have a gas station in my driveway, that would involve draining the tank into gas cans, and then refilling the whole tank.

I'm not much of an electrical guy, but is there a way to trick the gauge into thinking it's reading a 0-90 Ohm sender by simply using a resistor in the sender line (e.g a resistor that reduces the resistance by 33%, I guess)?

Or do I have to do the fuel drain-fuel fill thing?

I know very little about electrical stuff but I did have a quick thought since I know a little about e30 fuel level senders.

It might work out if you pulled the sender (or senders if you have two in your model) and held them right side up to simulate empty and then flipped them upside down to simulate a full level. I think they get their resistance reading from the simple float inside the cylinder so I would try that first. It might only get you 'close enough' but would only take a couple of minutes.

I might be way off in my thinking, and apologize if that is the case...

tb wrote: I know very little about electrical stuff but I did have a quick thought since I know a little about e30 fuel level senders. It might work out if you pulled the sender (or senders if you have two in your model) and held them right side up to simulate empty and then flipped them upside down to simulate a full level. I think they get their resistance reading from the simple float inside the cylinder so I would try that first. It might only get you 'close enough' but would only take a couple of minutes. I might be way off in my thinking, and apologize if that is the case...

Actually I was just now thinking about the same thing, so maybe we're both really smart (or really clueless)

If great minds think alike, does it follow that simple ones do, too?

I have been frustrated that this generation of BMW senders are neither the most elegant nor robust bits of hardware ever made. At least, they are blessedly easy to get at... especially in a 4 door with no seats!

If you wanted to get fancy with it and avoid some small spillage of gasoline, you could probably jumper the harness to trick it into thinking what you want it to.

Set the empty with an empty tank, pour in a few gallons and drive it to the nearest station to fill it up and set full?

EDIT: Upon further thought, you could just take a 60 ohm resistor and wire that in place of the sender for your empty, and then short the two wires and set the full mark.

In reply to Kenny_McCormic:

That sounds to be like the best idea.

If you add a resistor to the circuit to bump up the resistance of the sender, the tank won't read full.

0 ohms is for empty on both, so if you put a 0-90 gauge on a 0-60 tank it's only going to read 2/3 tank when full and empty should be fine.

I probably wouldn't even worry about it. Hook it up and go, calibrate later if you want to.

Doh, read the resistance the wrong way around. You're right.

Still advise against the resistor as it won't ever read empty...

oldopelguy wrote: 0 ohms is for empty on both, so if you put a 0-90 gauge on a 0-60 tank it's only going to read 2/3 tank when full and empty should be fine. I probably wouldn't even worry about it. Hook it up and go, calibrate later if you want to.

I'll note that this is a digital gauge (showing % full) and I'm already driving a car without a working odometer or speedo, so when I'm doing long drives to events I'm already having to calculate speed based on RPM. And since this may also be a stage rally and/or track car at some point, I'd just as well have the gauge read correctly so I don't have to think or remember things, lol.

In reply to irish44j:

The Autometer programmable fuel level gauge installation instructions describe how to reset the input to what you have. Here is a link to that manual: Installation instructions

wclark wrote: In reply to irish44j: The Autometer programmable fuel level gauge installation instructions describe how to reset the input to what you have. Here is a link to that manual: Installation instructions

yeah, I have the paper copy of that sitting on the table in front of me, lol (I bought the gauge new). The "right way" is to do the programming with the full and empty fuel tank (stated in the instructions). I'm just trying to avoid getting a bunch of fuel in cans to do that, since the car isn't terribly mobile right now.

Can you remove the fuel level sender and move it manually to program full and empty?

Edit: didn't read the whole thread first. Ignore me.

^^ I just dug around and found my spare fuel sender in a drawer, so I should just be able to hook that up and turn it upside down to simulate a full tank without getting gasoline everywhere, lol.