[willisodhiambo]

I have a friend whose N46 engine in X1 2.0 litre consumes 1 litre for every 4.3km. Town driving, short distances. No way this engine should consume that amount of fuel. Even my 535i N55 does 6.5km to the litre within town or with heavy foot.

Something is just not right here but we cant find any issues
1. Lambda is spot on 1.0 both adaptive and multiplicative
2. Valve stem seals replaced recently as car was smoking, now exhaust clean.
3. New plugs, new coils.
4 airmass sensor reading look plausible, air temp at MAF ok
5. Air pressure sensor readings ok
6. Compression test passes with flying colors.

Car drives fine, revs fine but just consumes a little too much fuel. Trip meter shows 4.3km/litre. Actual measurement, car cant do more than 280km for full tank.

Only thing I can think of is a blocked cat but no apparent loss of power as would be expected with a blocked cat

What else can I look at? Even attempted to tune dme for lean burn, same consumption!! Cant risk telling someone to decat and same problem persists

[Node]

"Lambda is spot on 1.0 both adaptive and multiplicative"!? Are you sure lambda control is working at all? I would bet that it never switches on as this is very improbable. Have you verified that with exhaust gas analyzer? Is thermostat ok?

[willisodhiambo]

"Lambda is spot on 1.0 both adaptive and multiplicative"!? Are you sure lambda control is working at all? I would bet that it never switches on as this is very improbable. Have you verified that with exhaust gas analyzer? Is thermostat ok?

Yes, lambda spot on does not mean it is static. It is very close 0.95 - 1.0 - 1.05. Replaced O2 sensors once before! We don't have exhaust gas analyzers in my country so that wont do.

Thermostat ok, temperatures read ok and look very probable.

I have gone over each and every dme function. All look very fine. Stumped.

[Florissilfhout]

Air intake / inlet manifold clean?  
Exhaust open (not blocked)?

[willisodhiambo]

Air intake / inlet manifold clean?  
Exhaust open (not blocked)?

Exhaust has been my suspicion. Car owner says they took it to exhaust shop and they passed the cat converter as OK. Intakes OK and clean

[user0086]

Are you sure the fuel is consumed by the engine and not leaking from the tank or maybe even stolen by someone? Sounds very unlikely that you have full power and lambda 1.0 but still that high fuel consumption.

Also, you don't need an exhaust gas analyzer, a wide-band lambda sensor with a controller and tailpipe sniffer is a cheap and effective alternative for an exhaust gas analyzer for diagnostics and tuning. You can even take it on the road.

[willisodhiambo]

Are you sure the fuel is consumed by the engine and not leaking from the tank or maybe even stolen by someone? Sounds very unlikely that you have full power and lambda 1.0 but still that high fuel consumption.

Also, you don't need an exhaust gas analyzer, a wide-band lambda sensor with a controller and tailpipe sniffer is a cheap and effective alternative for an exhaust gas analyzer for diagnostics and tuning. You can even take it on the road.

No leakages. Car has check emission fault now. Will scan and see. It may lead me somewhere. Will see if i can get a lamdal sensor

[Node]

I was thinking about the leak too, but then trip meter should not take that into account. Unless they do now? Have you looked at the plugs recently? I mean are they clean, of right color, etc?

[willisodhiambo]

I was thinking about the leak too, but then trip meter should not take that into account. Unless they do now? Have you looked at the plugs recently? I mean are they clean, of right color, etc?

Yes, plugs burn OK and are new. O2 sensors are new, dme and egs flashed to current ileve. The near perfect lambda suggests excellent burn so I don't get why it consumes that much fuel. It makes little sense.

I still think it has something to do with the cat because of the worn valve stem seals that have now been replaced. Maybe the oil partially blocked cat, just enough to allow it to appear like it is OK?

It has thrown an absolute pressure fault but that was yesterday. The consumption issue has been there for over 6months.

I will use a compression test gauge to check exhaust back pressure at pre cat o2 hole. I think that will give me an insight into the cats condition.

[Florissilfhout]

I'm thinking in the other direction:
Does the car coast OK? Maybe the brakes are not disengaging fully or maybe there is some other form of increased drag (tires, wheel bearings, internal resistance in the gearbox, differential, etc.).

Something to check when you're done checking the exhaust