The beef with GDI and valve coking

[DEEZUZ]

So I honestly haven't looked much into the issue, but know EVERYBODY loses their minds when it comes to this. Maybe I'm missing something, but wtf is the big deal? Is everyone worried about the tiny tiny barely noticeable flow decrease due to coking or are there bigger issues here?

Cause I don't see it. Discuss.

Click to read more...

 

[Yaj Yak]

i just read a few quick things about it after reading your posts.

Gum and Carbon Deposits

Issues surrounding gum residue and carbon build up. Top Tier Gasoline.

blog.lubetech.com

Gum Residue

A compression test revealed low or no compression on some cylinders. Removing the valve covers and observing valve movement revealed some lazy moving valves or no valve movement on some cylinders. Pulling the cylinder heads and removing the valves revealed a gum-like residue, which was restricting valve movement. This contamination is especially a problem on low mileage engines with tight tolerances. A high mileage engine with excessive wear may not be affected. The condition is more pronounced once the engine cools down and the gum-like residue solidifies, forming a sticky, gummy-like substance. The problem with the fuel was determined to be a lack of anti-oxidants and deposit control additives necessary to prevent the formation of gum. This is common with fuel that has been in storage too long or blended improperly. Some of the engines required major mechanical repairs as they were interference engines.



Carbon Build-Up
Another issue that is becoming a common problem is carbon build-up. Detergents and deposit control additives are added to the fuel to help prevent the formation of carbon deposits on the intake valves. This condition is especially a problem with Gasoline Direct Injection (GDI). With this system, fuel is injected directly into the combustion chamber instead of on the face of the intake valves, which provides a fuel wash for any contaminates. Valve overlap further promotes the accumulation of deposits, as some combustion gases are forced past the intake valves promoting carbon build-up.

Carbon deposits promote misfires, rough idle, long crank times and no-start conditions. In some cases the engine will run rough for a few minutes and then perfectly until the next cold start. The reason is the carbon accumulates in a porous form and initially absorbs the fuel, creating a lean condition. Once the carbon becomes fully saturated with fuel, the engine will run perfectly. These deposits can collect on the fuel injectors, affecting their spray pattern, resulting in hard starts, misfires and excessive levels of hydrocarbons and carbon monoxide.

The carbon deposits can cause an increase in the compression ratio, often requiring a higher octane fuel to prevent spark knock. This can be a problem with turbocharged engines as the boost pressure increases the compression ratio to a level resulting in violent detonation. Higher compression ratios can results in pre-ignition of the air-fuel mixture, resulting in detonation. Carbon knock can also result due to the pistons making contact with the carbon deposits.

 

[Yaj Yak]

also somewhat related- i was also just reading GM has a patent on an integrated oil seperator assembly.

GM Patents Innovative New Integrated Oil Separator Assembly

It's essentially a second oil separator mounted to a primary oil separator.

gmauthority.com

In Plain English
If all that engineering jargon is too much, here’s an explanation in simpler terms: the crankcase ventilation system will vent air out through a first oil separator, and – through the use of check-valves – it may continue to a second oil separator. The direction of the air is dictated by blow-by flow passages, and the separated oil is returned through drain passages.

The air vented from the crankcase can go to one or more openings, including an air intake system which can include a turbocharger. The second oil separator can include a pressure regulator valve that can regulate the system’s pressure via check-valves.

 

[OffshoreDrilling]

Anything direct injection has the same problems. BMW horribly misfired under load, worse fuel economy and poor throttle response.

I did a diy walnut blast. There were deposits on the backs of the valves close to 1/4” thick in some spots.

 

[EmersonHart13]

If I recall correctly your DIY was also very successful at cleaning them?

 

[OffshoreDrilling]

Messy but easy. Pull the intake off, $40 harbor freight sand blaster with walnut media also from harbor freight. BMW vac/blast nozzle that is contoured to the shape of the intake port.

blast the cylinders with the valves closed,vac out media, bump the starter to close the next set of valves and repeat.
3-4hr job

 

[EmersonHart13]

I do miss your endeavors with that car, lots of good stories/content from it

 

[OffshoreDrilling]

It’s all for sale, $100 and I’ve got leftover media too!

 

[DEEZUZ]

Yea, I mean I've ported heads before with them on the engine so I can def rug something up. I'm still not 100% sold on this being a catastrophic issue

 

[OffshoreDrilling]

I do miss your endeavors with that car, lots of good stories/content from it

Between that car and boat, I was lighting money on fire.

 

[OffshoreDrilling]

Seriously. I saved $10k in like three months as soon as I ditched that fucking car. Boat wasn’t that expensive just endless amounts of back breaking contortion to work on it.

 

[OffshoreDrilling]

I miss the car but not the boat.

 

[EmersonHart13]

I am talking car only here... Boat just seemed like a nightmare.

I also miss your V10 Super Duty. Regular Cab, Long Bed.... Something about that truck was just right.

 

[OffshoreDrilling]

Another truck as soon as I’m in a house. Extended cab long bed full size 4wd high mile non Chrysler product. Like the shit Outlaw is always selling for $6-8k

 

[OffshoreDrilling]

I do miss your endeavors with that car, lots of good stories/content from it

I miss a lot of the projects I did with the cars I had. Dumb “unique” stuff.

TBSS AWD to 2wd conversion
DIY trans build 6l80 in the denali
Stupid BMW Turbos

 

[EmersonHart13]

Oh yeah, the trans build was awesome

 

[bikrboy128]

Seriously. I saved $10k in like three months as soon as I ditched that fucking car. Boat wasn’t that expensive just endless amounts of back breaking contortion to work on it.

but i thought bmws were cheap to own and never break

 

[Kaeghl]

I recall toyota adding a an extra injector to the intake just to wash the valves with fuel during operation.
the audi's v8 and v10 have huge issues with coking. There was a guy in the r8 forums that lost about 30% of power (on dyno) due to how thick the valves were coated.

 

[OffshoreDrilling]

but i thought bmws were cheap to own and never break

Never made such claims!

 

[DEEZUZ]

HEY TAKE THIS SHIT TO ANOTHER THREAD YOU FUCKING ASSHOLES.

 

[OffshoreDrilling]

Sorry for thread crapping.

cliffs: valve coking is an issue. Deal with it accordingly.

 

[b4black]

BMWs and Mazdas had serious issues early on. The deposits were enormous and choked off air flow. Everyone either became super paranoid and/or used this as a way to bash DI technology. Same applies to LSPI (low speed pre ignition).

After I bought a 3.5 Ecoboost, I read about it being a must to get a catch can. But if you look at people that have had their intake manifold off for what ever reason, the valves don't look too bad. The MAP sensor hole is a perfect location to slide in a borescope and take a look at the valves. I'd do this before wasting hundreds on a catch can.

Don't fix problems you don't have.

 

[Thirdgen89GTA]

Yeah, LSPI gets blown out of proportion. Its a real thing, but the way they talk about it you should never, EVER get into boost under 3000rpm because you'll detonation and blow all the rivets of your floorboard out.

But I never had a lick of issues with any of my turbo cars.

 

[Great White Drake]

Probably doesn’t do much but I seafoamed my di Kia. The cloud of smoke stopped traffic on a busy street. It was fun as hell.

 

[bikrboy128]

yea, seafoam usually doesn't help. the buildup is way too hard for seafoam to break it down.

i see alot of hype around this issue, but not many vehicles that come through my shop having a noticeable issue. maybe it will get worse down the road