I have a 2011 Modus 1.5DCi with 4K on the clock. For the last 2 months, I've noticed the smell from the exhaust is really bad, like disgusting. I've worked around buses and lorries most of my life so I know what diesel smell is. I cant smell it while I'm in the car only when you step out or stopped at traffic lights when the window is down. It passed the MOT last month so I guess the co2 emissions are ok. The only thing I can think of that may be causing it is last August I made a batch of Biodiesel, about 20 Lts using new veg oil to see if the car would run OK on it. The car run fine on 50/50 biodiesel mix, I had no problems. I'm just wondering if it has damaged the catalytic converter.