Hi,
I have a 2012 Kia Pro Ceed 1.6 CRDI diesel (D4FB engine). The car is just shy of 100,000 miles and has been serviced regularly. This year I installed a new air filter and fuel filter when servicing.
I log all of my fuel and noticed a bit of a general decline in recent months, not massive but noticeable. Here is a chart of rolling average MPG of the last 5 fill-ups:
chartAdditionally, I notice frequently on the instant MPG display that the car is getting lower MPG when on flat motorway using cruise control whilst previously this would always be greater than the limit of the display at ~60mpg.
The car otherwise runs okay, tyres are inflated appropriately, I did get 4 new tyres a year ago but not sure how much difference they could make. The tyres have the same C fuel rating. There is not excessive amounts of stuff in the boot etc.
The roads are not to different, generally reasonable runs on motorway or other large roads with plenty of cruising at 60-70mph.
Having had a read around I understand oxygen sensors going bad can be a common cause of reduced economy. I have a cheap OBD reader and downloaded some free software but looking for some advice on interpretation.
Here is a chart of the voltage and equivalency ratio of the O2 sensor in the exhaust manifold. Whilst cruising along on flat motorway the voltage tended to hover around 0.6V, which I understand is slightly rich?
Any advice on interpreting this data and other things to consider that may contribute to worsening economy?