[ddeliber]

I recently purchased a 335d, my first BMW and I am loving it but I have an odd and concerning issue. Basically it noticeably and regularly runs with reduced power and uses more gas. Its not like it goes into limp mode or anything, it just won't hold speed at the same throttle level.

Using the only piece of real time data that I have at the moment, when it is running what I believe to be normally it will maintain speed (highway at say 75 mph) when I apply enough throttle so the mpg gauge is showing 50mpg. However, when it is acting up, I need to give it more gas (to say 35mpg) just to maintain speed. Initially I thought that this was because doing a DPF regen (or whatever it is called), but this happens almost every day and I thought these regen cycles are supposed to happen every 700 miles or so. I know the instantaneous MPG gauge isn't the best or most reliable thing to use, but it is all that I have at the moment, and it should be pretty consistent for the same daily route with minimum traffic.

Since I started paying attention, I have only been able to capture 3 or 4 normal/good commutes into the office (consistent all the way door to door performance) yielding around 34 mpg. Most of the time, the issue shows up somewhere during the drive (same drive every day, 22 miles about 35min) and I get between 25 and 29 mpg. Now that I am paying attention it is easy to see when the issue starts and it is really getting me concerned that there is something wrong.

It is at the dealer right now for a few issues and when I told the SA about this he said that they would take a look. However, he seemed to indicate that they were just going to plug it in and check for any codes. Based on the way he described what they will try and how he said it, I am not to confident that they will really do anything here. He did a key read and showed me that there are no open campaigns on the car and I saw that the EGR and the subsequent DDE update (SI B13 04 12) recalls were done.

Does anyone have any thoughts on what is going on or has anyone seen anything similar? Any suggestions on how I can describe this to them so that they have something to look at instead of just saying something like no codes so nothing to do?

Thanks.

[Kamando]

How many miles are on the car?

[ddeliber]

23k

[Kamando]

That doesn't seem to be enough miles to have the carbon build up that I had http://www.e90post.com/forums/showthread.php?t=770163 so you should be ok there; especially if all the recalls were completed and you have relatively low miles.

I guess see if you can find the Cetane rating of the diesel fuel you are using. I believe the national minimum is 40. A lot of states are in the 40s. BMW recommends 51 or higher for optimal performance I believe.

I would like to think you would have codes if it is an engine issue since you have the latest DDE update.

[ddeliber]

Yea, I sure hope it isn't carbon build up, that would really stink with my miles. Interesting about the cetane rating, I've tried a few places here in MA and everything I have found is 40.

By way of an update, the dealer did what I expected, no codes, nothing to fix. The lead tech did drive my car home last night and he got 34mpg home and 32mpg this morning in higher traffic. Not a surprise, every time something is not 100% reproducible, it seems it doesn't show up when I try to show someone else. I did ask for the gear box update that was mentioned in another tread and they said that they wouldn't be able to do it without a code or another reason to do a software update. However, since I am waiting for a part (a piece of trim) he suggested that I tell them how she is driving when I bring it back in and maybe I will have different luck with a second request with similar performance.

[tek4tex]

I'm convinced that fuel quality is a problem especially with winter blends. You might want to consider additives for not only better performance but also for protecting fuel system components. I think the fact that diesel is refined differently in Europe is the difference.