My 03 Lancer OZ Rally started getting bad gas mileage and the CEL came on a couple times. Both times the code is P0171 (Lean in bank 1). I hooked up EvoScan and the fuel trims are all reading 10-12% which I know is not normal. I'm not sure if there is a different map for Evo Scan for this car. I have the Evo Service manual which says P0171 will come on if the fuel trims are high for a prolonged time. Granted this is a Lancer having the problem, and not an Evo, but they seem to be similar enough in this regards.

Gas mileage used to be around 25-27 MPG, but it's now around 20-22.

I checked for vacuum leaks and replaced the front O2 sensor but the fuel trims are still reading high.

My next guess is the fuel injectors need cleaning or are somehow going bad. Is there a fuel filter in this car that needs to be replaced also?

I searched a few forums and injectors and vacuum leak seem to be likely culprits. Is there any way to diagnose the injectors using evoscan?

What other ideas do you guys have to investigate?

Thanks

 

Anyone have any ideas?

BTW, the car is completely stock. No upgraded injectors, exhaust, intake, or anything.

 

i have an 03 oz also and went through three quarters of a tank of gas in 190miles

 

cars just lose gas mileage as they get older but i still get 28- 30 mpg in my 02' LS. the fuel filter is in the gas tank. put some lucas fuel injector cleaner in and fill the tank up and see if that helps.