Got my Suzuki Swift Diesel serviced two months back, and all of a sudden the mileage dropped from 20kmpl to 12kmpl and that is confusing!
After i returned to Service shop, the guy said that there is nothing he could do about it because there is no such thing which can cause a mileage to drop other than the driving habits.
I personally dug and found that a choked air filter can cause car performance and mileage to drop (15% decrease) as for each gallon of fuel the engine burns, it requires upto 10,000 gallons of clean air. Therefore I cleaned it up (at the time of service the air filter was changed) and tried again to check if things get back to normal. Unfortunately, it didn't help!
So my question is, WHAT might be the causing this as the fuel injectors and everything else I know of is working fine?
How can I resolve this?
What other attributes are to be checked to make sure if everything is really Okay?
EDIT: Black smoke does actually is spitted out of the silencer usually when I push the accelerator (NOT too hard though).