I just rebuilt the engine and i've put about 1200 miles on it. It runs great but its getting crappy mileage, and i dont know why. Can anyone one help??? Any ideas???? The only thing that i have changed on the car since putting the engine back in is the tires. I got new tires that are a little bit wider than the old ones. Could this effect my millage??? Thanks for any help!!!!

The 5 things I would check are: brake drag - jack up each wheel and put in neutral with the e-brake off and check for ease of rotation; possible vacuum leak - pull off a vacuum hose while it's running; if it doesn't run worse, then you have a vacuum leak; rich carb? - are your plugs black?; wrong sparkplugs - just use ngk; bad oxygen sensor.

 

I just rebuilt the engine and i've put about 1200 miles on it. It runs great but its getting crappy mileage, and i dont know why. Can anyone one help??? Any ideas???? The only thing that i have changed on the car since putting the engine back in is the tires. I got new tires that are a little bit wider than the old ones. Could this effect my millage??? Thanks for any help!!!!

Mis-set cam timing, mis-set ignition timing. Does your engine have a carb or SPFI/MPFI? Model Year?

1990 Loyale with SPFI. And after looking at the engine I realized that the wire to the O2 sensor got pulled out during engine install. I'll fix that today and let you know what happens.

from personal experance that will definatly cause you to get horrable gas milage

running with the O2 sensor unplugged will affect the mileage, but it shouldnt make it run below 20 mpg.

 

If you are gettin over 20 mpg, stop complaining.. I get 12-15 mpg with my EA82

Now that you've plugged that O2 sensor back in, reset the ECU. Disconnect the negative on the battery, and hit the brakes (the brake lights will drain any power left in the system). Then wait like 10 minutes, and reconnect the battery.

 

This will force the ECU to set a baseline again without waiting for it to try and learn.

ecu's get very freakin slow over 10-12+ years. Patience prevails, learning does happen if everything is hooked up necessary.