[Tony B]

I have an E91 330D (2010) which I have had since almost new (now 64k miles).

Recently (last 6 months or so) the fuel consumption has increased significantly (by about 25%) so I have started to monitor stuff, using the BMW Drive Analyser app.

As well as running very cool (main thermostat now changed as a result) the lambda readings seem a bit odd.

On start up (cold) Lambda = 0.6 - fair enough for starting I guess.

Constant speed (70mph) cruising Lambda = 1.4

My question: should L not vary with varying accelerator demands? It is firmly fixed on 1.4, except when the cat heats up to just under 600C, during cat regen (I assume). At this time the Lambda becomes really sensitive to accelerator use (which I would expect it to be).

But at all other times when cruising or accelerating/decelerating normally it sticks to 1.4 exactly.

To me 1.4 sounds like it is running quite rich at constant speeds (it is a diesel remember), which might explain the heavy fuel consumption.

Oh, and it still takes a long time to warm up, in spite of the new thermostat.

Thoughts please!

[Tambohamilton]

Does sound a bit odd to me. Though I don't really know what it should be.

To me 0.6 sounds rich as...crazy. I thought 1.0 was pretty rich for a diesel?
1.4 sounds fair enough to me, but like you I'd expect it to vary with throttle input etc. Also, if you're coasting (engine overrunning), I'd expect infinite lambda (no fuel injected)?

[Tony B]

Originally Posted by Tambohamilton

Does sound a bit odd to me. Though I don't really know what it should be.

To me 0.6 sounds rich as...crazy. I thought 1.0 was pretty rich for a diesel?
1.4 sounds fair enough to me, but like you I'd expect it to vary with throttle input etc. Also, if you're coasting (engine overrunning), I'd expect infinite lambda (no fuel injected)?

Yes - I would expect infinite Lambda on the overrun, too.

I had another chat at the dealer, a different service advisor who did seem rather more knowledgable (known him for years) and he said that the DPF regen process was almost certainly not working at all for some time, due to the glow plug and glow plug control unit problems which were identified via fault codes.

As these have now been replaced the regen process should be working properly. I do not know how often it *should* work (whether it is proper closed-loop, or it is just done on an hours of use basis) but it has certainly been evident in the last 2 journeys undertaken, with lower gears being held for much longer, and the cat temperature going much higher than it has since I started monitoring. The water temperature also has reached higher levels than was typical, although I am not sure whether it is actually warming up quicker.

And Lambda varying much more obviously with accelerator movement.

I will keep an eye on things for the next week or 2, to see whether things improve.

Annoyingly, my M3 is also showing signs of thermostat problems as it is running water temps in the mid 70s, even when the oil temps are fully up to operating levels.

I can just imagine the eye-rolling I will get when taking this is in for attention next...

[Tambohamilton]

Dpf regen runs closed and open loop - will be triggered by back pressure/calculated soot mass, as well as roughly once a tank. Bear in mind that it won't happen if you have less than 1/4 tank of fuel (IIRC)