Why no carbon or other trouble?

[lmichael]

So watching as technology of gasoline engines starts changing as well as that of diesels and they become "closer". For instance. Many gas engines use GDI (gasoline direct injection). Similar to a diesel. Fuel injected at precise moment for proper combustion. Yet gas engines using this are plagued with issues. Foremost is intake valve carbon deposits. Why not with diesels?
Diesels using what has been basically a trouble free emission system on gas engines EGR. On a modern gas engine it exists with basically no trouble yet on a diesel a nightmare
Finally turbo chargers. Gas engines? Nightmarish issues and shortened engine life. On a diesel? No issues.
This stuff has me SMH a lot

 

[GreensvilleJay]

1) diesel fuel is not as clean burning a fuel as gasoline
2) gas turbos.... obviously not designed or built properly

 

[Borane4]

1) diesel fuel is not as clean burning a fuel as gasoline
2) gas turbos.... obviously not designed or built properly

The idea that diesel is not as clean-burning is thrown around a lot, but never explained. It really is not. Gone are the days of a diesel engine belching black smoke. That was due more to the engine design than the fuel, and maybe the fact that it had higher sulphur than gasoline. Diesel is more weight efficient and modern engines designed to burn it are more thermally efficient. Diesel is arguably a "cleaner" fuel.

 

[GreensvilleJay]

Come on up here and get behind ANY triaxle dump truck,highway hauler or city bus !! You'll need new wipreblades PDQ ! I'm not talking about 'rolling coal' toys..those OBVIOUSLY don't meet ANY emission standards !

 

[RBsingl]

The problem of carbon deposits is GREATLY overblown with properly designed GDI engines. I bought my first GDI equipped gas vehicle many years ago (2008 Cadillac CTS with 3.6L) and have owned many since and currently have three GDI gas powered vehicles.

There is a HUGE difference between cosmetic carbon buildup and sufficient buildup to in any way impact engine performance/operation. Some of the early designs (i.e. BMW) had severe issues with carbon buildup but today the hysteria over carbon buildup in GDI engines largely fuels another typical automotive industry group of products and services that exist only to separate a driver from his money. Take a look at the huge number of older GDI cars on the road today that have never had any sort of carbon removal "therapy" and are running just fine.

Rodger

 

[lmichael]

IDK, It must be something. Since now companies like Toyota are using dual systems to fight it. From what I've seen it does not seem to be cosmetic either. In any case still puzzling why, it seems to be in gasoline engines yet not seen in diesel. I know while in the rental industry we saw huge amounts of engine troubles with them on all different makes. Some so bad getting them past 20k miles without a huge service was hard. Although it seems to have one common denominator. Oil. Seems blowby and such is the main culprit. Maybe air oil separators are the answer? I never noticed. Do diesels have that type of thing? I gotta think the blowby in a diesel is more than in a gas engine with less than half the compression ratio

 

[Biker1mike]

My GDI Kia requires either Tri-clean fuel or the use of techtron every 5K miles. I do both and have no issues. Sometimes it pays to actually read the owners manual.

 

[dirtydeed]

dual squirters on/in my 5.0 liter coyote (port and gdi). What could go wrong?

 

[TheOldHokie]

So watching as technology of gasoline engines starts changing as well as that of diesels and they become "closer". For instance. Many gas engines use GDI (gasoline direct injection). Similar to a diesel. Fuel injected at precise moment for proper combustion. Yet gas engines using this are plagued with issues. Foremost is intake valve carbon deposits. Why not with diesels?
Diesels using what has been basically a trouble free emission system on gas engines EGR. On a modern gas engine it exists with basically no trouble yet on a diesel a nightmare
Finally turbo chargers. Gas engines? Nightmarish issues and shortened engine life. On a diesel? No issues.
This stuff has me SMH a lot

Generalizations are dangerous.

I have a twin turbo BMW with GDI engine. Those engines routinely go hundreds of thousands of miles and if you are picky about the idle might benefit from a walnut shell blast every 100K or so. Mine has 135K on it and has never been touched. The last I checked the local garage wanted roughly $1K for a blast. Thats about what they charge for a 4 wheel brake service. A valve cover gasket was 8 hours and double that.

We have owned 3 different GDI BMW s, two with twin turbos, with similar results. I think the "problems" are way overstated.

Dan

 

[RBsingl]

My GDI Kia requires either Tri-clean fuel or the use of techtron every 5K miles. I do both and have no issues. Sometimes it pays to actually read the owners manual.

Techron or equivalent (found blended in "top tier" fuel) is an excellent fuel system cleaner but does nothing to address carbon buildup on the back of intake valves which is where people go nuts over carbon in GDI engines. Because a GDI engine injection is direct into the combustion chamber, no fuel mix flows around the intake so no amount/type of fuel cleaner has an impact.

For the hybrid direct plus additional port injection engines to provide cleaning of the intake valves, there must be sufficient fuel flow both in terms of quantity and frequency of event over the intake valve to have any impact. Two primary reasons for using hybrid systems are to provide sufficient fueling at maximum power when the capability of the DI system is exceeded (GM has used this version in limited applications including the highest output Corvette engines) and I recall at least one of the Japanese manufacturers experimented with minimal application of port fuel injection at idle to improve idle quality but I doubt that either of these systems will have a significant impact on carbon buildup on the intake valve because of the minimal and infrequent fuel mixture flow from the intake manifold.

Again, with properly designed engines this buildup doesn't rise to the point of actually impacting performance and I personally never plan to use my intake valves as eating utensils so absolute visual cleanliness doesn't concern me.

A more important consideration with GDI engines is using oil designed to reduce the incidence of LSPI (low speed pre-ignition) which is something that forced induction GDI engines are especially prone to experiencing. Although primarily an issue with forced induction engines, it can happen with the typical high compression ratio used in some normally aspirated GDI engines. (i.e. some generations of GM's 3.6L V6 including those used in my 2014 ATS and 2021 Camaro use a 11.5:1 compression ratio and the same was used for some of the naturally aspirated members of the LT family of V8 engines). LSPI is more damaging than typical knock because it results in fast combustion before the compression stroke is complete.

Rodger

 

[Joisey]

The problem of carbon deposits is GREATLY overblown with properly designed GDI engines. I bought my first GDI equipped gas vehicle many years ago (2008 Cadillac CTS with 3.6L) and have owned many since and currently have three GDI gas powered vehicles.

There is a HUGE difference between cosmetic carbon buildup and sufficient buildup to in any way impact engine performance/operation. Some of the early designs (i.e. BMW) had severe issues with carbon buildup but today the hysteria over carbon buildup in GDI engines largely fuels another typical automotive industry group of products and services that exist only to separate a driver from his money. Take a look at the huge number of older GDI cars on the road today that have never had any sort of carbon removal "therapy" and are running just fine.

Rodger

I partially agree with you. Have you ever seen the youtube channel I Do Cars? He tears down engines and shows you what failed. Some of the intake ports on these engines with GDI are half closed with carbon. I have a 2018 Tacoma V6 that has both port and GDI. I took the intake off to change the spark plugs at 50 K. Looked down the ports with a borescope. The ports have a blush of carbon on them which wipes off with a rag, the back of the intake valves are spotless.

 

[RBsingl]

There are some engine designs that were terrible in terms of buildup but hopefully none of the manufacturers are making those same bad design decisions now.

There are a lot of people wanting to sell products and services addressing a non-problem. Maybe a lot of them have gone to Facebook with duct cleaning service now given the epidemic of that critical service complete with dramatic photos of the horrible monsters just waiting to jump out of your HVAC ducts while you are sleeping.

Next stop will be microscopic buildup on the windings of electric car motors as the terror of the day thus making the future safe for the sale of services

Rodger

 

[The Evil Twin]

Valve overlap.

 

[Vigo]

RBsingl covered it, but im going to add a (hopefully) somewhat lower-level, simpler explanation.

Modern cars are far more tightly emissions regulated than the vast majority of diesel engines in history were, or are currently. A major part of what is controlled is 'crankcase emissions', ie blowby gases. Since the 1960s gas cars have been sucking their crankcase gases through the intake manifold, across the intake valves, and 're-burning' them through the combustion chamber to reduce those emissions. In doing so, oily, carbon-heavy 'gases' deposit some of the solids they are carrying onto the manifold surfaces and the back of the intake valves.

Prior to GDI, all gas engines had gasoline flowing through either the whole intake tract from throttle valve to intake valve (as in carbs and throttle body injection) or at least had gasoline flowing over the intake valve (port fuel injection). Since gasoline is a good solvent, it continually 'washed' those contaminants off and through the combustion chamber, and things stayed reasonably clean.

With GDI, there is no longer necessarily any fuel in the intake tract (some GDI are also port injected as RBsingl mentioned) but we still have the blowby gases, so crud accumulates.

Part of the solution is far more complicated PCV (positive crankcase ventilation) systems which include 'cyclonic oil/gas separators' and other jazzy names for things which do a better job separating the solids from the gases before it reaches the intake tract. Other improvements are to cylinder sealing, i.e. leaking less blowby in the first place with better piston ring function and fitment, etc.

 

[cthomas]

I have done several walnut shell blasting on engines that would have a mystery misfire engine issue after other techs/shops have sold tune-ups, coils, timing chains, fuel injectors, fuel pumps, and one shop replaced the alternator(could not figure that replacement out). Yes, the VW/Audi 2.0 and the GM 3.6 are the engines that I have adapters for(use a universal for other engines) Also have used GM top engine cleaner and used a pump to spray into intake as the engine is running to duplicate the effects of the old multiport fuel injector back of the intake valve cleaning. Kind of depends on what I can see with the borescope and customer's budget/level of risk.

 

[RBsingl]

If the alternator was a 3.6 in a Cadillac CTS, I am not too surprised. GM uses a fuel and battery saving alternator control algorithm in all of their gas powered vehicles but the particular version of this system used in the CTS causes some really weird issues when the alternator is developing issues and these are issues that wouldn't normally be associated with alternator problems. So shops that have any tendency towards throwing parts instead of diagnostics have "replace alternator" high on their list with this engine/vehicle combo.

Rodger

 

[mikester]

Generalizations are dangerous.

I have a twin turbo BMW with GDI engine. Those engines routinely go hundreds of thousands of miles and if you are picky about the idle might benefit from a walnut shell blast every 100K or so. Mine has 135K on it and has never been touched. The last I checked the local garage wanted roughly $1K for a blast. Thats about what they charge for a 4 wheel brake service. A valve cover gasket was 8 hours and double that.

We have owned 3 different GDI BMW s, two with twin turbos, with similar results. I think the "problems" are way overstated.

Dan

A BM-Trouble-U that goes hundreds of thousands of miles? I'd like to know more. I'm guessing on the back of a cargo ship, tow trucks usually put a limit at a hundred miles or so.

 

[TheOldHokie]

A BM-Trouble-U that goes hundreds of thousands of miles? I'd like to know more. I'm guessing on the back of a cargo ship, tow trucks usually put a limit at a hundred miles or so.

I thought I was pretty clear - 135K on my 2007 335xi right now. Thats "K" as in a hundred thousand. Its my daily driver and not at all unusual. The straight six N52, N53, and N54 engines have proven to be very reliable designs.

Dan