I have a 91 318iS body with an M20 motor, the car also had an S14 in it at one time. The gauge cluster is from a 325 (6 cylinder) so the tach is right. The gas gauge only shows 1/2 when empty, the warning light comes on and it is indeed empty. I swapped the sending unit from a known working car and the gauge behaved the same, only ever showed 1/2 at empty. Yes, it shows full when full but never less than half. Any ideas?