My OBD Sensor reading (using a one from 'Torque') displays a value when the  car is running and fully warmed up of around 3 to 4 :1 which is very low considering that the air fuel ratio of diesels should be around 14.7:1 to 15:1 . The 1.2tdi polo 6R is standard and has no smoke and runs ok apart from a little roughness between 1 and 2 thousand RPM and fuel consumption is around 50mpg which is a bit low for a bluemotion  model. I suspect the Oxygen sensor  is faulty...any ideas?

Edited 17 October, 20214 yr by robzrr
Typo

Update- replaced MAF sensor - car now runs smooth. AFR now displays 9 when fully warmed up

Still only getting around 50 mpg average , even driving gently. 

My OBD Sensor reading (using a one from 'Torque') displays a AFR value of 8-9 on tickover and an 02 variance of 0.5-0.6 when the  car is running and fully warmed up . This is still  is very low considering that the lambda air  should be around 14.7:1 . The 1.2tdi polo 6R is standard....Car runs fine with no warning lights .Hmmm

Volkswagen Polo (2009 - 2017) 1.2 TDI BlueMotion - Real MPG | Honest John

suggests average of 57mpg is seen by people who reported.

 

Manufacturer claims are dubious as from test conditions on new car.

 

I'd take out and clean the EGR valve which will be impeding flow from intercooler with soot if it has been running rich.

I used Lucas 41019 EGR and Turbo cleaner spray. Half can on the car, some when removed and a scraper.

I also found summer economy on the diesel was better with no engine undertray (Skoda octavia 1.9tdi), but I don't have an engineering explanation, except that perhaps the cooling pump does not have to work as hard, so lower parasitic loss.

Winter consumption is worse, slower for engine to reach operating temp.

 

Driving at 2000rpm to 2500rpm in highest gear possible, high tyre pressures, least dead weight, letting the car roll up to junctions in high gear all help.