Carbon build up with direct injection

[tybalt]

This appears to be a significant problem for some engines:

http://www.audizine.com/forum/showthread.php/33635...

Oil and unburnt fuel is added to the intake from the crankcase by the crankcase vent. It hits the hot intake valve and sticks, and a sooty mucky buildup results, which can stop the valve from properly closing, or restrict the intake.

In a direct injection engine, no fuel is present in the intake to wash the deposit off the valve.

If this is such a problem for FSI/TSI engines, why isn't it a problem for TDI and other diesel engines?

Better oil separators? Something else?

Confused.

[MoBeanz]

Hmmm, interesting. Lots to read there. Thanks.

[Crusoe]

Lots of talk of rs4s loosing 100bhp or more because of this, expensive to clean out every 20k miles if you wanted to make sure it stayed running perfectly.

[Crusoe]

Regarding the diesel option I think the DPF(Diesel Particulate Filter) cars pass some fuel through to burn off the carbon every so often which may stop the build up but also seems to cost quite a bit in mpg.

[HellDiver]

Crusoe said:

Regarding the diesel option I think the DPF(Diesel Particulate Filter) cars pass some fuel through to burn off the carbon every so often which may stop the build up

I think you need to find out how a diesel engine works, because this is cobblers.

[thinfourth2]

HellDiver said:

Crusoe said:

Regarding the diesel option I think the DPF(Diesel Particulate Filter) cars pass some fuel through to burn off the carbon every so often which may stop the build up

I think you need to find out how a diesel engine works, because this is cobblers.

I think that with a diesel they either have a late injection or a seperate injector to burn the DPF off.

If you inject the diesel late enough it will piss straight through the exhaust valve while it is open

[HellDiver]

thinfourth2 said:

HellDiver said:

Crusoe said:

Regarding the diesel option I think the DPF(Diesel Particulate Filter) cars pass some fuel through to burn off the carbon every so often which may stop the build up

I think you need to find out how a diesel engine works, because this is cobblers.

I think that with a diesel they either have a late injection or a seperate injector to burn the DPF off.

If you inject the diesel late enough it will piss straight through the exhaust valve while it is open

Exactly, none of it goes near the inlet manifold, which is what Crusoe was suggesting happens.

Oddly enough, DPF is why VW had to abandon PD and go Commonrail - because PD injectors are powered by the cam shaft, they were having difficulties getting the cam to power the injectors long enough after the initial injection to satisfy the DPF's need for post injections. This is why the DPF PD engines (particularly the PD170) have such a problem with the DPF clogging. Commonrail can inject at any time, so can chuck plenty of diesel out during the exhaust stroke.

[Crusoe]

Sounds like both suffer the same then with the blow by gases and exhaust gas recirculation fed into the inlet tracts and accumulate. In both cases, since the engines are direct injected there is no fuel passing through to keep the stuff dissolved though maybe the increased compression on the diesel and more sooty exhaust stop it being such a hardened on consistency and therefore not quite as big an issue as the petrol engines, or the rev band they work in isn’t such an issue as the top end power loss on a petrol. Wouldn't have a direct injected petrol or diesel myself anyway though VW/Audi seem to be getting a lot more grief about it than other manufacturers.

[inman999]

I had one of the mitsubishi GDI engines that date back to the late 90's. They used to coke up pretty badly. I used to whip the intake manifold off and clean it out every so often, you could then get carb cleaner directly onto the intake valves without any further dismantling. A bit of hassle but compensated by the mid 40's mpg and decent power output.

I've heard that Japanese fuel is much cleaner and negates many of the problems we see in the UK.

[tybalt]

Crusoe said:

Sounds like both suffer the same then with the blow by gases and exhaust gas recirculation fed into the inlet tracts and accumulate. In both cases, since the engines are direct injected there is no fuel passing through to keep the stuff dissolved though maybe the increased compression on the diesel and more sooty exhaust stop it being such a hardened on consistency and therefore not quite as big an issue as the petrol engines, or the rev band they work in isn’t such an issue as the top end power loss on a petrol. Wouldn't have a direct injected petrol or diesel myself anyway though VW/Audi seem to be getting a lot more grief about it than other manufacturers.

All diesels are direct injection - it's not just VAG ones. How is the increased compression and sooty exhaust going to stop buildup on the intake?

[David911RSR]

I had an RS4 and the carbon build up issue takes hold way before 20,000 miles.

[Defcon5]

Cant they just put a catch tank on the PCV system? I have one to stop my TB from getting clogged up and it works very well

[tybalt]

David911RSR said:

I had an RS4 and the carbon build up issue takes hold way before 20,000 miles.

Anyone know why it's such an issue for the RS4 and not for other direct injection engines? Maybe because it's a high performance engine and absolutely needs the intake to be tip top to achieve full power? Or perhaps more blow-by or something?

Still confused about why it's a problem for some engines and not others.

[tybalt]

Defcon5 said:

Cant they just put a catch tank on the PCV system? I have one to stop my TB from getting clogged up and it works very well

That does seem the obvious fix, but I'm not clear on whether it's normal on diesels for example?

BTW whats a TB? Tuberculosis can't be right, but that's what springs to mind.

Edited by tybalt on Friday 29th October 22:21

[ASR1]

Is this a VAG-specific issue or should owners of any direct petrol injection vehicle be worrying?

[Defcon5]

ASR1 said:

Is this a VAG-specific issue or should owners of any direct petrol injection vehicle be worrying?

A lot of reported problems seem to be VAG, is that due to them selling more direct injection units though?

tybalt said:

Defcon5 said:

Cant they just put a catch tank on the PCV system? I have one to stop my TB from getting clogged up and it works very well

That does seem the obvious fix, but I'm not clear on whether it's normal on diesels for example?

BTW whats a TB? Tuberculosis can't be right, but that's what springs to mind.

Edited by tybalt on Friday 29th October 22:21

TB - Throttle Body

[El Guapo]

I recall reading on one of the Porsche forums a lot of discussion about how the move to DI on 911 motors is going to cause headaches, specifically loss of performance and increased maintenance costs.

[tybalt]

ASR1 said:

Is this a VAG-specific issue or should owners of any direct petrol injection vehicle be worrying?

You'd think that the same principle would apply to all direct injection engines. Hence the question. Like someone said above, there's been a lot of discussion on Porsche DI engines.

[The Wookie]

It's also considered to be a problem on lastest model Mini Cooper S and Works engines.

Also some have commented on fuel quality, it's worth pointing out that if the crankcase breather theory is correct it physically cannot be related to fuel quality. In a direct injection engine, the valves are not exposed to fuel.

Personally, I think it's an EGR issue in which case it could be related to fuel quality, but it's tenuous. I'll ask our local combustion expert later on for his opinion.

[Sticks.]

I'm no tech but stumbled across this on the TT forum. Although essentially an ad, and I'm not promoting it in any way, it's an interesting little vid fwiw http://www.vimeo.com/3989681

More here http://www.tt-forum.co.uk/forum/viewtopic.php?f=2&...