# Can a diesel use a "catch can"?



## BB_cuda (Nov 8, 2011)

I've been reading a thread over on the E90 normal forum as in gasoline DI engines. Specifically, people are opening up their intake manifolds and cleaning gunk off of their intake ports and intake valves. The thread explains becuse the engines are direct injected rather than port injected that the intake ports are not continuously cleaned by fuel. 

I know the very nature of diesel is different but none the less we are direct injected as well. The thread talks about the oil vapor coming from the crankcase PCV valve getting up into the intake system. One guy comments that if a "catch can" is put in down stream of the PCV valve that the problem goes away.

Will this work for us D people too? i know our EGR valve recall had to do with crap building up on it. what scares me more than anything is the turbos and intercooler getting full of crap. 

Please keep discussion relative to catch can and not off to our often discussed EGR recall. We beat that to death (pulverised is a better word) in another thread already.


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## Axel61 (Mar 10, 2011)

Great question I had a catch can on my 02 MCS. I frankly dont know we need one but if so let someone start this


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## floydarogers (Oct 11, 2010)

Although you might be able to fit a catch-can without screwing up the emissions controls, that won't solve the problem. And, BTW, direct injection has nothing to do with this; diesels have been direct injection for over 100 years without ever having any carbon buildup problems.

The problem is seemingly caused by the EGR (Exhaust Gas Recirculation) system that reduces O2 in the intake stream, which then lowers NOx emissions. You can't screw with that without removing the EGR valve and re-programming the DDE (ECU).


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## Snipe656 (Oct 22, 2009)

floydarogers said:


> Although you might be able to fit a catch-can without screwing up the emissions controls, that won't solve the problem. And, BTW, direct injection has nothing to do with this; diesels have been direct injection for over 100 years without ever having any carbon buildup problems.


I don't think all of them have been in the past 100 years. For example the OM616(used in the 240D back in the early 80s) from Mercedes I do believe was an "indirect injection".


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## F32Fleet (Jul 14, 2010)

Pointless with the EGR system sitting there.


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## 62Lincoln (Sep 26, 2004)

Question for the assembled masses: instead of removing or plugging the EGR valve, would it make more sense to have a plate made to cut off the flow of gases right at the exhaust manifold itself? Naturally, the EGR valve would need to be coded out too.


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## Snipe656 (Oct 22, 2009)

62Lincoln said:


> Question for the assembled masses: instead of removing or plugging the EGR valve, would it make more sense to have a plate made to cut off the flow of gases right at the exhaust manifold itself? Naturally, the EGR valve would need to be coded out too.


This I believe is how my friend bypassed the EGR on his old service truck. He thought he was going to have to get the ECU reprogrammed but actually ended up not having too.


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## BB_cuda (Nov 8, 2011)

floydarogers said:


> diesels have been direct injection for over 100 years without ever having any carbon buildup problems.
> QUOTE]
> 
> Thanks Floyd, yes I'm aware diesel has been doing the direct injection a long time. I tried to distiguish that point in my original starter thread. So, if I'm reading carefully, the gasoline guys are getting full of crap related to oil from PCV whereas in some cases our system is getting dirty from exhaust gas return. Is this right?
> ...


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## Snipe656 (Oct 22, 2009)

BB_cuda said:


> Is the carbon buildup issue gone now?


I do not think anyone can honestly answer this question. It seemed more speculation that the recall was specifically done because of the carbon buildup issues some people had that resulted in top end motor replacements.

My take on this in general though is even if the recall fixed the issue from happening with a 100% properly working system it does not mean that later on down the road that something might start functioning incorrectly after wear/use/time and cause the buildup. This actually is what happened on my truck a few years back.


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## BB_cuda (Nov 8, 2011)

*link to DIY valve and intake cleaning*

http://www.n54tech.com/forums/showthread.php?t=12258

Post # 80 (page 4) talks about the catch can and there is a link to Burger who sells them.

There are many photos of nasty intake ports and very caked up intake valves. Burger claims this can be eliminated if catch can is used. This may have nada to do with our D engines but wanted the community to be aware of this on the 335i engines. Enjoy, its a bit of a read.


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## floydarogers (Oct 11, 2010)

BB_cuda said:


> There are many photos of nasty intake ports and very caked up intake valves. Burger claims this can be eliminated if catch can is used. This may have nada to do with our D engines but wanted the community to be aware of this on the 335i engines. Enjoy, its a bit of a read.


I personally have no need to read that - it has been discussed in the E9x forum multiple times. (Virtually all of the posters here read the E9x and/or X5 forums, as that's where the other 60% of the problems that occur on our cars get discussed.) IMHO, the perceived need for a catch can is driven by failures of the CVV, particularly failures in the M54 engines, which had to be redesigned for the N engines. A properly functioning CVV should catch all normal blowby.


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## BB_cuda (Nov 8, 2011)

Thanks Floyd. I read over there also but had not been aware of the M54 issue. I have only been a "Fester" for about a year though. So, new news to me and old news to you all.

Dumb question. What is a CVV?


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## Snipe656 (Oct 22, 2009)

BB_cuda said:


> Thanks Floyd. I read over there also but had not been aware of the M54 issue. I have only been a "Fester" for about a year though. So, new news to me and old news to you all.


I actually tend to not read the other sections so anything that gets cross posted in here can often be new news to me.


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## floydarogers (Oct 11, 2010)

BB_cuda said:


> Thanks Floyd. I read over there also but had not been aware of the M54 issue. I have only been a "Fester" for about a year though. So, new news to me and old news to you all.
> 
> Dumb question. What is a CVV?


It's a fancy name for PCV: Cyclonic Vapor Valve or something like that. It's what BMW put in the PCV valves to keep the oil vapors from getting to the intake manifold. The one on the M54 was poorly designed and would plug.


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## stokerdog (Sep 27, 2012)

*Catch Can Experience*

I wanted to weight in on this thread as I have some direct experience with this.

A catch can that I used and am familiar with is a "filter" that goes between the Engine crankcase (usually at the valve cover) and the intake tract. It's purpose is to give any particulate in the PCV system a chance to drop out before the air is returned to the intake system to be burned at the next combustion cycle. The stuff in there is oil mist and combustion by products - more on this later.

This air handling system is call the PCV (Positive Crankcase Ventilation) and is there to reduce pollutants. Old vehicles used to just vent this air to atmosphere.

Three Items were brought up that may help clarify this discussion:
1) How the fuel gets into the combustion chamber has no ( or very little) bearing on what is in the PCV air system. As a side note: Diesels have only been using direct injection for about 12 years, before that the fuel was injected into a "pre-combustion chamber". My first diesel, a Olds Delta 88 was 5.7 L and made 105hp, our 3L BMW's are at 265 thanks to two items: Turbo Charging and direct injection.

2) The EGR system was never used in the older Diesels and only in the last ~10 years to clean up emissions. The EGR is used to reduce the combustion temps (if there is less oxygen then the combustion will be cooler). These exhaust gases, in diesels, carry some carbon particulate matter with them. Generally not a problem as it is moving fast and does not stick well to intake systems.

I have attached a photo from my 2009 335d with 85K on it. I pulled the intake last week to perform the BMW service bulletin for the Swirl Flap Actuator - Clip. I was not surprised to find the build up as I had a VW TDI with 218K on it and had cleaned the intake and EGR cooler a few times. A catch can will give a greater opportunity for the oil in the PCV system to drop out before it is re-introduced into the intake, where it combines with the carbon from the EGR system creating a very tar like substance that likes to stick to the intake.

A catch can should not affect the computer at all as the system is not disrupted at all, just a slightly longer route. If you look up compressed air filters, the catch can is exactly the same idea. I made one using a water filter I pick up at my local ag supplier- the one from Burger is a nice looking example. Based on how oily the carbon build up was in my intake, the BMW CVV is not adequate so I will be installing one in the next few months.


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## Snipe656 (Oct 22, 2009)

stokerdog said:


> 2) The EGR system was never used in the older Diesels and only in the last ~10 years to clean up emissions. The EGR is used to reduce the combustion temps (if there is less oxygen then the combustion will be cooler). These exhaust gases, in diesels, carry some carbon particulate matter with them. Generally not a problem as it is moving fast and does not stick well to intake systems.


Been more than 10 years. My 1985 300SD has an EGR on it. Also it has been awhile since I looked at my extra engine for this car but for some reason I am remembering it being direct injection. Quick search of google seems to support that thought but I did not go reading hard on the subject.


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## BB_cuda (Nov 8, 2011)

@ stoker: Is the photo looking back up into the intake runner? The little box that highlights when I move my mouse of the photo says "335d air intake". This doesn't look like the port for the intake valves from my earlier link to n45tech.com. As long as the catch can doesn't harm anything and does collect/condense oil vapor, it has to be a good thing to consider doing. But, it is a matter of the vapor being cool enough to condense the oil out of the crank case gas flow. I'm a thermal analysis guy at my job so I wonder what the saturation temp of oil is at the crank case pressure which can't be much higher than atmospheric pressure. Boiling point goes up as pressure increases. Condensation temp is same as boiling point it's just happening in the other direction thermodynamically.


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## stokerdog (Sep 27, 2012)

When I serviced the heads in my 1980 Delta 88 Diesel I had no major carbon build up, nor do I recal the ERG Valve, I have had little experience with Benz's so I will concede that they may have been using the EGR to control temps already. One thought is that where the Exhaust Gases are re-introduced may have a large effect on partical fall out. In a V8 they get introduced into the intake manifold (inside), where as our BMW's (and VW's) get introduced at the outside of the intake after the EGR Cooler.

Looking at the outside of the engine is a very difficult way to determine if it is an indirect or direct fuel injection as the injectors are both on the head. I attached a picture of a head with pre combustion chamber from an indirect injection car.


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## 62Lincoln (Sep 26, 2004)

I *think* I recall reading elsewhere that EGR also has the purpose of reducing Nox in modern diesel engines. Is that correct, or am I misremembering?


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## Snipe656 (Oct 22, 2009)

I actually have an extra engine for my MBZ and have the head pulled. Next time I am out where it is stored I am going to have to look at it. Pretty certain it is DI and now become curious about it.


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