Direct Injection huge drawback

[thescreensavers]

So over on the GTR forums there was a discussion about DI and some guy was asking why the GTR doesn't have it. Apparently it has a huge drawback as you can read about below. I really never understood why the ISF had both port and direct injection, now I know! Good thing Lexus had the foresight to see this problem unlike many of their rivals (audi, bmw etc)

Anyway here is the post:

I hope the GT-R never gets DI until they figure out a way to prevent power robbing carbon build up on the valves/intake manifold.

The fuel does not wash over the intake valves, thus oil and other bypass product in the intake manifold that gets recirculated for emissions control sticks to the valves and cools there turning into carbon sludge and then baked on carbon deposits.

One of the biggest reasons I traded my 2007 RS4 in for my GT-R was because of direct injection and the carbon build up. It took that car from an amazing all around all weather high performance luxury sedan and made it a normal S4 with a body kit. Not to mention all the trips to the dealer, the intake manifold replacements(the low/high rpm air tumbler flaps seized due to carbon build up) and having to pay for the carbon cleaning on my dime when I only used the Audi approved oil, Shell V-Power 93 Octane and Audi's own fuel treatment/injector cleaner.

Here are some pictures.

Close ups of the rock hard carbon deposits on the valves/valve stems/valve ports:

Carbon covered intake manifold flaps:

Before many hours of soaking in solvent and plain old elbow grease/scrubbing:

After many hours of soaking in solvent and plain old elbow grease/scrubbing:

http://www.nagtroc.org/forums/index.php?showtopic=39598


Thats some crazy carbon buildup

 

[Howard]

Jesus Christ. There must be a way around that.

 

[evident]

that's nasty

 

[overst33r]

I've seen that on the 2.0T from VW as well.

I'm curious if BMW and other companies have the same issues...

 

[alpineranger]

I think toyota gets around this a little bit on their DI 3.5L v6 by having additional port injectors too (although that wasn't the initial motivation for the design). Don't know about their 2.5L DI engine which doesn't have the additional injectors.

 

[LTC8K6]

GM doesn't seem to have the problem, or they've done a good job hiding it.

 

[franksta]

I think there's something else wrong with that motor.

All of the carbon from combustion has to pass over the exhaust valve (or blowby the piston rings!) and those don't have the almighty injector blasting them with fuel.

EDIT: And none of the stuff above the intake valve (the flappy things) have the fuel on it either with a port injection setup.

 

[StageLeft]

VW can't build a reliable vehicle to save their life anymore I'm afraid.

Anyway, how many miles to get that kind of deposit?

 

[LTC8K6]

It's mostly oil vapor from the crankcase vent system depositing on the back of the intake valves, iirc.

These vapors are capured and burned in modern engines. Port injection continually washes these deposits off the intake valves.

Direct injection doesn't, unless you have a second port injector, as some mfgs do.

 

[ayabe]

Ms3's have the same problem, seen plenty o' pics floating around.

 

[EightySix Four]

Haven't seen problems on the LNF from GM with this.

 

[halik]

Yeah people with the DI motors have all sorts of issues with it. Even my S4 had a fair bit of caking on it, but the RS4 needs cleaning at least every 10K

 

[TwinsenTacquito]

VW can't build a reliable vehicle to save their life anymore I'm afraid.

Seen blueprints of their stacked cylinder engines? Tissue paper cylinder walls.

 

[shabby]

Haven't seen problems on the LNF from GM with this.

It seems like its only a vw/audi problem, i looked at my valves with a fiber scope and all were good, no deposits on them after 25k miles.

 

[EightySix Four]

It seems like its only a vw/audi problem, i looked at my valves with a fiber scope and all were good, no deposits on them after 25k miles.

I think it's a VW/Audi driver problem. Nothing like WOT to clean out some carbon.

 

[Vette73]

Yea that is not a DI problem, that is a either a engine design problem or soemthing wrong with that car. GM, Toyota, etc... do not have that issue. But this is a VW/Audi so what do you expect.

Every time I see a VW/Audi fanboy it always ends with saying "but they fixed their problems, they are good now..." and then things like this crop up.

 

[PricklyPete]

Yeah...I've seen this. There seem to be fairly huge threads on this on every VW/Audi forum. I have heard that other manufacturers are having this problem as well...but I have nothing to back that up...so I'll say that is a rumor for now. If this does prove to just be an VAG thing...wonder if VW/Audi will do anything after enough people complain. I'm not holding my breath.

 

[PricklyPete]

Yeah people with the DI motors have all sorts of issues with it. Even my S4 had a fair bit of caking on it, but the RS4 needs cleaning at least every 10K

I didn't realize the B6/B7 S4's had direct injection...for some reason I was thinking only the RS4 version of the engine did. Interesting.

 

[AsianriceX]

I didn't realize the B6/B7 S4's had direct injection...for some reason I was thinking only the RS4 version of the engine did. Interesting.

Here's a reference for VAG folks:
http://www.audizine.com/forum/showthread.php?336352-Audi-FSI-Engine-Carbon-Build-up-Megathread

Looks like Porsche isn't immune either:
http://forums.rennlist.com/rennforu...the-new-gt3-doesnt-have-direct-injection.html

I've heard that Mazdaspeed3/6 guys are having the same issues, but I'm too lazy to look that up right now.

 

[EightySix Four]

All the affected DI motors have exhaust gas recirculation systems. Explains why the GM DI motors have no problem.

 

[SparkyJJO]

All the affected DI motors have exhaust gas recirculation systems. Explains why the GM DI motors have no problem.

So they still don't have it? Wasn't sure. My 98 has EGR but I know some later ones don't.

 

[PricklyPete]

All the affected DI motors have exhaust gas recirculation systems. None of the GM motors do, explains why the DI V6 and me and Shabby's LNF have no problems.

Very interesting.

 

[EightySix Four]

So they still don't have it? Wasn't sure. My 98 has EGR but I know some later ones don't.

They claim the C-VVT removes the necessity.

Cam phasing also provides another effective tool for controlling exhaust emissions. Because it manages valve overlap at optimum levels, it eliminates the need for a separate exhaust gas recirculation (EGR) system.

I don't think it's the oil that is the problem, which explains why catch cans aren't as helpful as everyone expects. It seems obvious that the exhaust gas is filled with too much shit and there's no fuel to wash it off. Wonder if someone can make EGR delete systems like diesels have?

 

[Bignate603]

They claim the C-VVT removes the necessity.

If they're passing current emissions regulations without EGR it sounds like they're right. After having to clean out EGR valves on multiple cars I wouldn't mind getting a vehicle that doesn't have one.

 

[Ronstang]

It's mostly oil vapor from the crankcase vent system depositing on the back of the intake valves, iirc.

These vapors are capured and burned in modern engines. Port injection continually washes these deposits off the intake valves.

Direct injection doesn't, unless you have a second port injector, as some mfgs do.

Then they need to have exhaust scavengers take care of it like I do on the cars I build. You end up with a great running engine that has no build up and no contaminating of the air/fuel charge and you can retrofit these to any car....no passing emissions is another issue.