I have a 92 FD3S and for some weird reason after owning the car for less than 9 months, my mpg dropped from 17-18mpg all the way to 10-11mpg. I havent done anything but replace a couple of vacuum lines. Stock ECU, stockport, stock turbos and injectors. I know I am slightly behind on spark plugs and oil change. Vacuum is at 17-18(whatever vacuum is measured in). I dont drive it any differently than when I first got it but it is my daily so I notice just about every slight change. My exhaust too hot sensor broke so I have the warning light on the dash but I dont think it would cause me to run rich. I can basically smell raw fuel coming out of the tail pipe at idle. Compression is good above 110psi on a 73k motor. What do you guys think happened?

 

when the ECU thinks its too hot, it dumps fuel in, and turns off the air pump to try and cool it down.

 

Ahhhhh thank you. Looks like I will be fixing that today.