direct injection gas engine intake port deposit build up

[Tmoose]

Sounds like direct injection gasoline engines will experience significant build up of deposits in the intake ( and exhaust?) ports well before 100,000 miles.

BMW has a walnut blasting tool that supposedly fits on the intake manifold for reduced dis-assembly for service.

There is talk of adding air oil separators in the PCV system.
There is talk of special Valvoline oil that reduces the problem.
There is talk of using -30 or -40 oil in place of -20 being helpful.
There is talk the build up is primarily a low rpm/light load problem, to the point some manufacturers now add port injectors that are used for some operating conditions.

Experiences and comments welcome.

thanks,

Dan T

 

[lucky-guesser]

I don't know why it would build up on the exhaust any more than normal. The build up is on top of the valve because it is not getting cleaned off from the former port injection. The top of the exhaust valves were never getting sprayed so I don't see a difference there.

Dual injection seems to be increasingly common, though still rare. I can't remember all of the load/temp conditions for when it will run which but some of the nicer semi-performance cars will switch back and forth.

 

[TugboatEng]

Diesel engines have been direct injection since their inception. Carbon buildup in the intake ports has not been a problem for them. What is the difference between a diesel and gas engine? The throttle. Diesel engines have no throttle so port velocities are always high which helps keep the ports clean. To keep your gas engine ports clean you need to operate the engine at wide open throttle as much as possible.

 

[Lou Scannon]

Hi Tug, I'd like to understand better how throttling (i.e. at the intake manifold) reduces port velocity (all other things being equal). Please elaborate.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[gruntguru]

It doesn't. Reduces air density in the port. Volumetric flow rate and velocity stay the same.

Do diesels have pcv systems? They can't be manifold vacuum driven.

Fuel added in the port both cleans the valve and reduces its operating temperature. High temp is what bakes on the deposits.

Water injection would probably prevent the problem.

je suis charlie

 

[3DDave]

Seems like a vacuum sucking** oil down the valve guides is the more likely culprit. It's not much but it doesn't take much. WOT reduces the pressure difference.

**Really, external pressure pushes the oil because of the reduced push-back from the low pressure side, but "suction" is fewer words.

 

[TugboatEng]

That was a good question and I was totally incorrect about velocity. Thanks for the correction, grunt. Think about overdrive transmissions. They maximize throttle opening but minimize engine speed. They don't help this situation. I should correct my comment and say that you need to rev your engine higher and more often. Diesel engines have a very narrow powerband which forces you to operate them closer to their maximum speed.

Yes, diesel engines have PCV systems. They use the air filter to create a pressure drop to draw crankcase vapors into the intake. Marine engines didn't always get this feature which gunked up our engine rooms. I have installed the Parker Racor CCV systems on all engines in my fleet.

My understanding is that gasoline does have alkyds in it while diesel does not. You may recognize alkyd from the term alkyd enamel. It's literally the varnish that forms inside of the engine. Diesel engines never form varnish, we get soot instead.

3DD, I would tend to disagree with the valve guide leakage. Again, many diesel engines don't have intake valve guide seals. They don't have port fouling issues.

 

[gruntguru]

Ah but they don't have manifold vacuum - usually positive pressure in fact.

je suis charlie

 

[TugboatEng]

I turbocharged my truck recently. It's a diesel. I tapped into the the intake ducting for crankcase ventilation. This engine has a crankcase depression regulator but I don't really understand it's importance. It has a wire mesh type oil separator in the valve cover.

 

[BrianPetersen]

Emission controlled diesel engines with crankcase ventilation and EGR certainly have had intake clogging problems. VW TDI engines in the rotary-pump era (first generation of them) certainly had issues with this.

https://www.youtube.com/watch?v=g_78_MNvhy4

The newer models got better fuel injection and combustion systems, producing less soot, and EGR systems that recirculate from after the DPF.

As for direct-injection petrol engines ... seems to vary. A lot of them are now using both direct and port injection to help clean the valves off. I doubt if air/oil separators or changing oil type will help much; if the engine isn't an oil-burner then there's not much to separate.

 

[TugboatEng]

Let's not use VW and BMW as examples of systemic problems because they have a history of inventing their own problems.

 

[dgallup]

We had to walnut shell blast a BMW engine intake valves back in the late 80's. GM was having big problems with injector plugging (almost nobody else was) and decided it was cheaper to take out full page adds in the WSJ blaming the oil companies than to figure out a way to solve their problem. The oil companies responded with new and improved detergent packages which kept GM injectors cleaner but caused BMW engines to coke up their intake valves. It's a very intricate dance between the various deposit formation mechanisms and the cleaning mechanisms. The current heavy EGR load and lack of GDI cleaning has caused a large resurgence in intake valve deposits. There are all kinds of different schemes to cool and clean EGR but the duel injection systems seem to be winning. Ford has it on all their EcoBoost engines now, Lexus has always done it on their GDI engines and it's filtering down to the Toyotas.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[TugboatEng]

FYI, my car is a 2009 Lexus IS250 which is prior to Toyota adding the port injector. This engine is known for clogging ports. I had the intake manifold off to do spark plugs at 100k. There was some buildup but not enough to warrant cleaning. The car is at 130k now. I bought the car with 90k miles so I don't know how it was driven prior.

 

[Factoter]

Internal EGR? Is this the main culprit here . . . described as carbon slag on intake.
If the Intake valve closing is causing back-flow, depositing particles then a catchcan is useless.
So droplet size and oil fuel chemistry is possibly preventative, as well as engine loading.

 

[SwinnyGG]

DI engines get valve deposits because the valve isn't being 'washed' by a constant spray of fuel, as it is in a direct port engine. This isn't a BMW/VW problem... it's present in basically every first generation DI engine platform. Fords, Chevys, Porsches, BMWs, Volvos, Toyotas, Hondas, they all do it.

 

[TugboatEng]

If it was specifically caused by a lack of "washing" why isn't it a problem in diesel engines?

 

[BrianPetersen]

Emission controlled diesel engines with crankcase ventilation and EGR certainly have had intake clogging problems!

The newer ones have better combustion efficiency (less soot) and a lot of the time, they now use a low-pressure EGR system that is recirculating from aft of the DPF. No particles, no clogging.

Also, the cam timing of diesel engines often has little or no overlap. If exhaust containing soot doesn't get to the back of the intake valve, it can't clog the intake valve.

 

[TugboatEng]

Sure, EGR can clog intakes but a lot of DI gas engines don't have EGR and still are prone to intake clogging.

The exhaust side of the engine has lots of soot and isn't so prone to clogging.

Diesel engines absolutely have valve overlap. I routinely use the valve overlap period to identify TDC which saves me having to do two revolutions of the engine after doing top end work.

 

[SwinnyGG]

If it was specifically caused by a lack of "washing" why isn't it a problem in diesel engines?

Multiple reasons.

1) the lighter hydrocarbon fractional components in gasoline that tend to create 'varnish' aren't present in high quality diesel fuel. They can be present in a lot of the waste oil streams people use as diesel substitutes, which is why people running engines on vegetable oil or used lubricating oil or whatever do see this problem pop up sometimes

2) gas engines operate with the manifold under high vacuum almost all of the time. Diesel engines have some pressure drop across the intake tract but it's an order of magnitude lower. Lower manifold vacuum means intake charge reversion is reduced by the same factor the vacuum level is. Intake charge reversion is what causes intake valve fouling

3) Gasoline engines operate at much higher air/fuel ratios. Generally they are targeting stoichiometric ratios most of the time. Stoich a/f for diesel is approximately the same as gasoline (around 14.7) but part throttle ratios for diesel engines, where they spend most of their operating time, approach 40:1

The combination of less intake charge coming back out and enveloping the hot intake valve in atomized fuel, plus less fuel available if there is any charge reversion, plus lower capability for that fuel to create varnish means little or no intake valve deposits.

 

[TugboatEng]

I agree that a lack of charge density and velocity is a root cause of deposit formation in gasoline engines.

Some spirited driving every once in a while is a solution.

Ester based oils can also help reduce deposit formation.