Hi, I have a superb 2 with a 2l diesel engine code CFFB. I did a long journey laletely and noticed the fuel estimation was 6.4l/100km but the actual consumption was 7.6l/100km, calculated between 2 refuelings.

2 months ago I had 2 of the injectors repaired in an professional shop. Could malfunctioning injectors be the reason? Anybody else noticed so much difference between estimated and real fuel consumption?

It is not unusual for the vehicles onboard fuel computer to read differently to actual calculated usage, often optimistic (as is yours) - very likely to be a calibration tolerance in manufacture.

AFAIK, the system measures the flow through sensors in the fuel line, so there is ample scope for calibration error.

I believe there is a method for adjusting the calibration via VCDS - a pity that there isn't a simple way for owner to apply an offset to fuel computer algorithm without using special tools.

Towing with a Yeti, going I had the wind behind me and it was mainly downhill,

coming back I had the wind head on and a lot of hills to climb!

That certainly made a difference to fuel consumption.

1 hour ago, Warrior193 said:

It is not unusual for the vehicles onboard fuel computer to read differently to actual calculated usage, often optimistic (as is yours) - very likely to be a calibration tolerance in manufacture.

AFAIK, the system measures the flow through sensors in the fuel line, so there is ample scope for calibration error.

I believe there is a method for adjusting the calibration via VCDS - a pity that there isn't a simple way for owner to apply an offset to fuel computer algorithm without using special tools.

Injector data id not used in the estimation calculation?

I don't think so, but I have seen references to fuel pump impulses being used to measure it.

11 hours ago, Racataian said:

fuel estimation

Which part of the term "estimation" is confusing you?

It is important to remember that one part of the fuel use equation is distance travelled - this is measured by the vehicles mileometer - which (in UK) is not permitted to under-read by any percentage at all, but is allowed to over-read by up to 10% - this means that the fuel use equation will almost invariably assume the distance travelled is up to 10% more than is actually the case. (Road Vehicle (construction & use) 1986)

Well th

1 hour ago, Paws4Thot said:

Which part of the term "estimation" is confusing you?

Well, I understand what estimation means but 20% difference to the real consumption is no longer an estimation, it's an error comming from somewhere. I have been driving for 550km, mostly highway with an average speed of about 120km/h, 3 persons and luggages. To consume 7.6l is not normal and I noticed it now after I repaired my injectors. Before I did not noticed a difference between real and estimated fuel consumption. In such driving conditions 6.2l was the normal. So now I am just try-ing to figure out if the injector repair was not done right or anything else is wrong

8 minutes ago, Racataian said:

3 persons and luggages

Do you always have 3 people and luggage?

I think there may be a coding process when fitting replacement injectors to this engine.

Perhaps the garage did not do this?

12 hours ago, Breezy_Pete said:

I think there may be a coding process when fitting replacement injectors to this engine.

Perhaps the garage did not do this?

That's what I suspected too, thanks !

As I could read earlier in this topic, the fuel consumption by default factory setting is on the optimistic side. Some years ago I used OBDeleven to achieve a realistic consumption level. At one point in time I made the decision to change my fuel injectors for new ones, and yes I had to code them also with OBDeleven. Once done, it did not have an effect on the measured consumption at all.