on board computer troubles, please help!!!!

[custom e30]

i pulled my engine and had it rebuilt and when i got the engine back and and car back running good i have the following symptoms...

1. if i reset the computer it will tell me how many miles i have lft in my tank at the beginning, but wont keep track of what ive used unless i reset again.

2. shows 0.0 for my average speed

3. show 5.9 for average gas

what could i have hooked up backwards?????

[Sir Smirnoff]

sounds like just the main sensor for speed. Idk what they use specifically, but it'd fix your 2nd symptom b/c it'd be getting a reading... it can't do #1 b/c it doesn't have a speed and I think 5.9 is a default... so whatever hooks up to the drive shaft to sense speed.