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So I have e21 with swapped engine and transmission from e36 1.8is, my fuel tank gauge is not working correctly, do you have any recommendations to how to fix it and see fuel level in the tank. Also I don’t have working speedometer as I have swapped transmission and stock e21 diff, what’s the best way to count speed. Any advices will be helpful.

Welcome! I believe there are GPS driven convertors that turn the GPS speed signal into a mechanical drive for the stock speedo, for instance see https://speedhut.com/accessories/sensor ... converter/

Yuji wrote: Thu May 29, 2025 4:34 pm So I have e21 with swapped engine and transmission from e36 1.8is, my fuel tank gauge is not working correctly, do you have any recommendations to how to fix it and see fuel level in the tank. Also I don’t have working speedometer as I have swapped transmission and stock e21 diff, what’s the best way to count speed. Any advices will be helpful.

I don't know how easy or hard it is in practice to adjust the voltage of the signal but here is what I did for mine. I put in an e30 if I remember correctly fuel level sender, or something of the same size as the original (still beamer) hoping it would just work, sadly it misread my tank level. Now empty is 1/2 tank and full is off the chart. While this does function I do want to fix it and as its a simple circuit one could just stick a resistor between the gauge and the sender to correct for the voltage difference. At least thats what I plan to do.
You also could have problems with the gauge or the wiring in between. And soaking the old sender in cleaner might free it up.
But with out more info I dont know what the problem is.