Extra thirsty engine? Lambda Sensor Issue?

[darkhorse1210]

Just back from a near 400 mile round trip in the RS2. As always the car was absolutely rock solid and made light work of the crappy conditions we drove through.

However, the friendly on board computer gave me and avg MPG for the trip of 19.8.

Now granted, we weren't in the slow lane the whole way but 90% of this journey was motorway miles.

Now I'm sure I've asked this question before but isn't this MPG more typical of booting it round A roads rather than motorway cruising? If so it is likely that my lambda sensor has carked it and it making the engine run too rich?? The cost of the lambda sensor would be covered quite quickly if I could get the engine running on less fuel!

All thoughts welcomed. Tom

[prj]

There "could be" lots of things wrong.

First thing is to check the car's rolling resistance, if anything is rubbing anywhere.
Second, log Group 000 on idle on VAG-COM to a CSV file and post it up, also check for faults.

Could be MAF, air leaks, FPR, lambda etc.

[Ross]

Pre-rebuild my RS2 was giving me about 21mpg average on motorway at 90-100, 25 mpg at 75-80. Daily commute (4 miles cold) was about 17mpg. So I'd say yours is a little low.

Post-rebuild & EV14s w/ PRJ remap I currently average the same 17mpg commuting, but last time I did a good motorway & A-road at good speeds with lots of misbehaving, I averaged 25mpg. At 75-80 29mpg.

As Dmitri says, VAG-COM it before splashing out on parts but I would say a quick MAF connector clean and boost leak check won't take much time and could give you a quick win.

[darkhorse1210]

PRJ/Ross

Thanks for the advice, I'll do some following up on this when I've got some time.

Ross - based on what you said I reckon it should have returned 22-23mpg without self incriminating myself

Tom

[UrS4boy]

In addition to the others's suggestions, you might want to consider the engine coolant temperature, either the real temperature is too cold (thermostat stuck open) or the perceived engine temp is too cold (G62 coolant sensor is malfunctioning). In both cases, the ECU will see the engine as cold and will enrichen the fuel mixture accordingly, making you fuel mileage readings go to sh*te.

Click on this link and then on the G62 label (top) and Thermostat label (right side) for more info (if you have an automatic climate control you can use it to check the real coolant temp - link in the Thermostat info):

http://members.shaw.ca/speedtek/UrS%20Engine%20Bay%20Device%20Map.html

[prj]

Agreed, if engine is not up to temp, it will also operate less efficiently due to more friction.

[UrS4boy]

Agreed, if engine is not up to temp, it will also operate less efficiently due to more friction.

That too but I think it will be minor compared to the ECU overfuelling because it thinks the engine is cold (G62 failure) or the engine is still cold (thermostat failed open).

[prj]

ECU does not dump that much more fuel in really.
Only when it's _really_ cold. If it's above 50-60C, then it should be fine.

So, with a messed up thermostat usually the high fuel consumption is more due to the engine not getting up to temp.
I haven't seen a lot of failed G70's which would not be detected by ECU, but never hurts to check!