# New 328d owner, preventing CBU??



## randchap (May 6, 2014)

Hey everybody,

First time BMW owner, got sucked into the brand by the 328d ads and am obsessed with my new wheels (new as of 2 months ago). Realizing already that I'm probably a BMW owner for life, it's obvious now how you can never go back to a "normal" car. I digress.

I have been interested in learning everything BMW so naturally started reading some of these forums, and lo and behold, I see all of these CBU posts. Lots of good info on how to clean it up, who to talk to, and what to do when you get the dreaded diagnosis.

That said, for those of us new owners, is there any consensus on how to prevent it? It sounds like a high pressure EGR issue, which means the 328d is in the same boat as the 335d unless there have been some mods since then I'm unaware of. Obviously there are some engine differences, will that prevent buildup?

Socal has high cetane diesel, which I thought was good, but then I read that it's maybe not good. I also read that you should drive it hard, but others say make sure you drive it long and warm. Lots of these ideas make sense logically but for every right answer there's another right answer and they both make sense.

I'm trying not to obsess about it, but if I can develop good habits now that prevent the issue down the road, I'm all about it. I'd love any feedback.

In the meantime, I'll just enjoy the ride!! I came from a 2006 Highlander with 175k on the odometer. No effort put into keeping that car running, yet I'm ok with a bit more maintenance for this ride!


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## DieselRacer (Apr 22, 2014)

I don't think driving characteristics matter all that much, CBU has been found in all type of driving mostly city but lots of highway cars clog also, I guess removing egr is a number one way to stop the problem or help it...who knows if it has a long term effect removing it and can you get it tuned out so no check engine light, and it would void warranty anyway...


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## F32Fleet (Jul 14, 2010)

I wouldn't worry about it. All diesels deposit soot at the intake side of the engine. It's a fact with EGR. Some engines are more tolerant than others. Hopefully some Brits can chime in because the N47 has been around since '07/'08.


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## m6pwr (Jan 26, 2008)

According to a guy on the Chevron Fuel Tech line, there is EPA no2 diesel and CARB no2 diesel. CARB = California Air Resources Board. CA CARB diesel is required to have substantially less aromatics than EPA no2 diesel - - about two thirds less - - and it's the aromatics that contribute to carbon and particulate emissions.


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## floydarogers (Oct 11, 2010)

randchap said:


> First time BMW owner, got sucked into the brand by the 328d ads and am obsessed with my new wheels (new as of 2 months ago). Realizing already that I'm probably a BMW owner for life, it's obvious now how you can never go back to a "normal" car. I digress.
> ...
> In the meantime, I'll just enjoy the ride!! I came from a 2006 Highlander with 175k on the odometer. No effort put into keeping that car running, yet I'm ok with a bit more maintenance for this ride!


Actually, your opening statement is not a digression at all - it's the reason we're all driving BMWs!:thumbup:

This CBU, while obviously a problem, is not worth obsessing about - I've got almost 80K miles on my 335d with no problems. Not to say I won't have problems in the future, but I certainly am enjoying the car.

My wife is going to get rid of her 2004 Highlander and buy a 328d xDrive sedan (no longer really need the extra carrying capacity). We've only got 122K on it, but it costs about the same to maintain as BMWs; don't know why people believe Toyotas are cheap in that regard.:dunno: And our Toyota T100, also at 125K, needed a new head: $4500 just last year.


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## DieselRacer (Apr 22, 2014)

floydarogers said:


> Actually, your opening statement is not a digression at all - it's the reason we're all driving BMWs!:thumbup:
> 
> This CBU, while obviously a problem, is not worth obsessing about - I've got almost 80K miles on my 335d with no problems. Not to say I won't have problems in the future, but I certainly am enjoying the car.
> 
> My wife is going to get rid of her 2004 Highlander and buy a 328d xDrive sedan (no longer really need the extra carrying capacity). We've only got 122K on it, but it costs about the same to maintain as BMWs; don't know why people believe Toyotas are cheap in that regard.:dunno: And our Toyota T100, also at 125K, needed a new head: $4500 just last year.


great review, thanks for the mileage update, good to know that our diesels can drive like a diesel should...


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## Hoooper (Jun 17, 2013)

m6pwr said:


> According to a guy on the Chevron Fuel Tech line, there is EPA no2 diesel and CARB no2 diesel. CARB = California Air Resources Board. CA CARB diesel is required to have substantially less aromatics than EPA no2 diesel - - about two thirds less - - and it's the aromatics that contribute to carbon and particulate emissions.


CA cars are in no way immune to carbon. Many on here and other forums from CA have had issues. I wouldnt be surprised if the 328d had fewer issues with carbon though, given the smaller engine it should require much lower EGR activity to meet the same nox levels


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## randchap (May 6, 2014)

Hoooper said:


> CA cars are in no way immune to carbon. Many on here and other forums from CA have had issues. I wouldnt be surprised if the 328d had fewer issues with carbon though, given the smaller engine it should require much lower EGR activity to meet the same nox levels


Thanks everybody! This actually makes sense. If there's less exhaust due to the 4-cylinder small displacement engine, there's less EGR. Definitely seems logical.

Definitely agree that it's not worth obsessing about. In this case, I'd say knowledge is definitely a good thing but not worth losing sleep over. It sounds like the walnut shell blasting runs around $1k anyway which over the life of the problem becomes a relatively small issue. And one that potentially could be covered under the CA emissions warranty as long as it rears before the 80k mark.


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## anE934fun (May 10, 2008)

m6pwr said:


> According to a guy on the Chevron Fuel Tech line, there is EPA no2 diesel and CARB no2 diesel. CARB = California Air Resources Board. CA CARB diesel is required to have substantially less aromatics than EPA no2 diesel - - about two thirds less - - and *it's the aromatics that contribute to carbon and particulate emissions*.


So far, this is the best candidate for joke of the week. The root cause of CBU is the EGR system, NOT aromatics content of the fuel. If aromatic content was the root cause of CBU, BMW and VW and MBZ would have been screaming their heads off about crappy fuel causing the CBU.


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## F32Fleet (Jul 14, 2010)

anE934fun said:


> So far, this is the best candidate for joke of the week. The root cause of CBU is the EGR system, NOT aromatics content of the fuel. If aromatic content was the root cause of CBU, BMW and VW and MBZ would have been screaming their heads off about crappy fuel causing the CBU.


Or the exact opposite because blaming it on fuel would mean that they purposely sold a car that was not suitable for the US.


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## listerone (Jul 21, 2009)

m6pwr said:


> According to a guy on the Chevron Fuel Tech line, there is EPA no2 diesel and CARB no2 diesel. CARB = California Air Resources Board. CA CARB diesel is required to have substantially less aromatics than EPA no2 diesel - - about two thirds less - - and it's the aromatics that contribute to carbon and particulate emissions.


I buy most of my fuel in Massachusetts because I spend a lot of time there and their diesel is *much* cheaper than ours .Are states that require California Emission levels (Massachusetts is one) also required to sell CARB approved diesel? Or is that just available in California?


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## Pierre Louis (Oct 23, 2011)

Unfortunately the joke is on us. To this day, there is no definitive study to prove what causes the carbon deposits in our engines, especially diesel direct injection

Here is a write-up that describes the problem as fuel related.

Here is a paper that, at least in gasoline direct injection engines, shows that higher load creates less carbon deposits.

We all know that in the 1980's BMW had problems in its gasoline engines regarding intake valve deposits. They found that certain fuel characteristics were important. Here is a brief summary of what was found.

My own question is whether using Castrol EXS LL-01 would make it more likely to have carbon buildup as opposed to Castrol EXS LL-04, as I imagine a lot of people don't believe there is any difference in premium oils and its easy to imagine a service tech choosing LL-01 for our 335d's as a matter of convenience!

Dunno. :dunno:


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## glangford (Dec 11, 2013)

anE934fun said:


> So far, this is the best candidate for joke of the week. The root cause of CBU is the EGR system, NOT aromatics content of the fuel. If aromatic content was the root cause of CBU, BMW and VW and MBZ would have been screaming their heads off about crappy fuel causing the CBU.


Actually from a chemistry standpoint aromatics are a little more stable than their alkane hydrocarbon analog and will probably burn a little cleaner. The EGR does it's job, it's just getting more soot from aromatic combustion products, so in essence aromaticity of fuel can be called a root cause.


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## Pierre Louis (Oct 23, 2011)

Here is an account that is looking at SAPS (sulphated ash, phosphorous, sulphur) content in engine oils as a major contributor, at least in gasoline direct injection.


> In summary:
> -DI engines have issues with deposits in the intake valve seats and stems.
> -Products of combustion contribute to this deposit.
> -Motor oils with higher SAPS content may be major contributors to this phenomenon.
> ...


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## Hoooper (Jun 17, 2013)

debating what the "cause" is between certain sources of ash is a bit like debating who is worse, the guy who stole $250 from 7/11 or the guy who stole $250 from the gas station. Who cares, theyre both thieves! The real cause is the EGR, without the EGR all of the aromatics, oil compositions, etc in the world wouldnt cause this ash/oil build up in the intake manifold.


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## Pierre Louis (Oct 23, 2011)

Hoooper said:


> debating what the "cause" is between certain sources of ash is a bit like debating who is worse, the guy who stole $250 from 7/11 or the guy who stole $250 from the gas station. Who cares, theyre both thieves! The real cause is the EGR, without the EGR all of the aromatics, oil compositions, etc in the world wouldnt cause this ash/oil build up in the intake manifold.


Who is debating?

What do you know that can tell us it is EGR?

How do you explain that many diesel engines with direct injection and EGR don't suffer from carbon buildup? What is the difference between these engines and ones that do get CBU? Both have EGR so that's not it.

Perhaps eliminating EGR is the only "cure" but that is not in debate. Perhaps there is a study showing this but I haven't found it.

Some of us just wish to know things, not debate about what we don't know.

PL


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## Hoooper (Jun 17, 2013)

A study? Maybe someone will do their thesis on the cause of carbon build up in the BMW 335d.

If you open up your manifold its undoubtedly caused by carbon from the EGR with ccv oil mist as a helper in binding. Logging the EGR activity may provide you with the reason the 335d has accelerated build up, demanding 100% practically all the time introduces a lot of soot.


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## anE934fun (May 10, 2008)

BMWTurboDzl said:


> Or the exact opposite because *blaming it on fuel* would mean that they purposely sold a car that was not suitable for the US.


I doubt that would be worth the effort, because a class action lawsuit would almost certainly result.


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## anE934fun (May 10, 2008)

listerone said:


> I buy most of my fuel in Massachusetts because I spend a lot of time there and their diesel is *much* cheaper than ours .Are states that require California Emission levels (Massachusetts is one) also required to sell CARB approved diesel? Or is that just available in California?


You would have to ask the state air pollution regulator whether they implement CARB for all fuels (CA mandates special bunker oil in ships running along the coast of CA...)? Just Gasoline? Or?


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## anE934fun (May 10, 2008)

m6pwr said:


> According to a guy on the Chevron Fuel Tech line, there is EPA no2 diesel and CARB no2 diesel. CARB = California Air Resources Board. *CA CARB diesel is required to have substantially less aromatics than EPA no2 diesel - - about two thirds less - - and it's the aromatics that contribute to carbon and particulate emissions*.





glangford said:


> Actually from a chemistry standpoint aromatics are a little more stable than their alkane hydrocarbon analog and will probably burn a little cleaner. The EGR does it's job, it's just getting more soot from aromatic combustion products, *so in essence aromaticity of fuel can be called a root cause*.


Ummm. Maybe I missed something - CBU is occurring in the intake tract (intake manifold + intake ports in the head). By the time the EGR valve gets exhaust to the intake tract, the presence/absence of aromatics in the fuel should not be relevant, because the fuel has been combusted. On a macro level, the process is as follows: crankcase blow-by gas + exhaust from EGR = CBU over time. This has been proven by owners who have blocked off the EGR - voila, significantly reduced (if not non-existent) CBU after the block-off.

Further, cars that have run CARB diesel their entire life are getting tagged with CBU. Just like cars that are not fueled with CARB diesel.


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