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Direct Injection Intake Valve Coking

JOV

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I know the LT1 and LT4 motors are direct injection but unlike ported fuel injection which fuel passes over the backside of the intake valve the DI remains dry from fuel. Will this be a concern down the line with valve coking as we accumulate mileage ???

It makes me wonder if GM has addressed this issue or has come up with a service procedure for the coking. I read BMW an Audi and VV are having valve coking problems on their DI engines .

I know my 2015 Z06 has a 5 year 100k power train warranty so I assume that if the valve coking affects the driveability during the warranty period it would be covered.
! So if anyone as any info on this It would be greatly appreciated ! Thanks in advance ! :beer
 

Hib Halverson

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Your understanding of what happens when the backside of the intake valves in a DGI engine get coated with an oil film.

As I understand the situation now many car companies which have direct injection engines in their products are struggling with this problem.

It will be interesting what they develop as a fix other than replacing cylinder heads under warranty. With GM, that's going to get old really quick. My guess is GM will do to Corvette owners with LT1 and LT4 engines what they did to Corvette owners with LS7s, ie: try and ignore the problem as much as possible and put the burden of proof on the owner as far as warranty claims. The only way to truly assess whether or not a GDI engine has coked up intake valves is to pull the intake manifold and inspect the valves. With LT1 you might be able to bore scope the engine, too.

I hope with the NA engine that GM comes up with some aftermarket solution one can spray into the intake manifold which will soften the coke deposits so they get sucked into the engine. With supercharged engines, I don't know what they could do other than pull the blower and the intake manifold then inspect the valves.

In many ways direct injection is a blessing but the intake coke problem is DGI's one curse.
 

JOV

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Hey Hib I was one of those C6 Z06 Corvette owners that GM let us fen for ourselves. My LS7 valves clattered from day one and it sounded like a loud sewing machine. After new heads , valves and rocker arms it was quiet as a mouse, after 6 months of normal driving valve clatter started over again. I thought to myself maybe I just rewound the clock. I just hope I am not repeating what I went thru with my 08C6Z06 with my 2015 Z06. I love this vette to much !! :thumb Just my $.02
 

LLC5

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DI not only has a tendency to coke intake valves, but the injectors themselves since they are directly in the combustion chamber. DI is good and efficient for power and mileage (CAFE), but the maintenance and repairs can be staggering if an owner has to pay for them. :)
 

kpic

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What I don't accept is GM or any of the others didn't know about the problem(s) in the first place. How Porsche missed their hand grenade problem is a good question.
OEMs test engines on a engine dyno, driving in circles on a test track, and actual road tests. Emission laws require various cycles, cold and hot weather testing; different driving (stop and go, sustained highway etc.) cycles. This is the validation of a design and every manufacturer does it.

During the development stage of an engine, everything is measured before assembly. After the engine is run on a dyno, they are disassembled and everything is measured again; then the measurements go to engineering.

As nothing is perfect, all components have tolerance; or the size is acceptable between 10mm plus or minus .1mm or any value between 9.9 and 10.1. Using Cpk (https://en.wikipedia.org/wiki/Process_capability) suppliers are "encouraged" to center their process to be as close to the nominal or 10 as possible or SQEs (supplier quality engineers) descend on them.
To know the amount of wear when new each part is measured. One might be 10.04, another 9.95 etc. After durability testing, the 10.04 might be 10.037 and the 9.95 might be 9.94. After disassembling what ever it is; it is hard to accept they don't have eyes. Very few mechanics measure when replacing a component; however, they see excessive deposits, odd wear patterns and more.

After all that, it is very difficult to believe "they," no matter who "they" might be, didn't know a coking or any problem existed. Where the system breaks down, is perhaps a supplier's production quality or materials aren't what was originally tested etc.

My guess is this process would be pretty much the same no matter what the end product would be.
 

xfirez51

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Aren't diesels DI? What happens to their valves? Does use of diesel fuel make a difference?
 

kpic

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Depending on the duty cycle, diesel engines coke also.

(Here we go again: let's blame everything on emissions :D)
Cars spend a lot of time at low loads, traffic, stop and go etc. To reduce emissions in those conditions, today's computers lean the engine which raises engine's temperatures; potentially causing oil build up (AKA coking) on the back of valves.
 

LLC5

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Depending on the duty cycle, diesel engines coke also.

(Here we go again: let's blame everything on emissions :D)
Cars spend a lot of time at low loads, traffic, stop and go etc. To reduce emissions in those conditions, today's computers lean the engine which raises engine's temperatures; potentially causing oil build up (AKA coking) on the back of valves.


Actually the feds, with their emission and CAFE standards, have forced the auto industry to make the most efficient engines ever (mpg and power) including diesels. I doubt if we would ever be where we are now with power and mpg without the feds (which sounds like government intelligence to me after writing it, oh well) interference. Blame it on emissions yes but power, reliability, and mpg would not be where they are now without the meddling federal agency's. Add cost to the consumer in there also, big time. :)
 

kpic

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Actually the feds, with their emission and CAFE standards, have forced the auto industry to make the most efficient engines ever (mpg and power) including diesels. I doubt if we would ever be where we are now with power and mpg without the feds (which sounds like government intelligence to me after writing it, oh well) interference. Blame it on emissions yes but power, reliability, and mpg would not be where they are now without the meddling federal agency's. Add cost to the consumer in there also, big time. :)


X2 and I totally agree. Where new vehicles are super impressive is their MPG. I'm pretty close in RWHP to the latest and greatest; yet, at 70 MPH in 6th, ~34 MPH. A far cry from my father's words it will pass anything except a gas station.

The only blame I assign to emissions is the heat.

Where I disagree is government intelligence as too often they prove a total lack thereof. It has been a long journey since the muscle cars, through the wings clipped years to today's vehicles.

Add a lot cost and close to a magnitude of complexity. ;)
 
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In the old days, we'd drizzle "Marvel Mystery Oil" down the carb with the engine running at a high idle and that would soften the coking on top of the intake valves and clean them up.

Guess I'll need to find a way spray "Marvel Mystery Oil" past the throttle body on all my new cars. :ugh

BTW, 26000 miles on my LS7 and I haven't noticed any problems with it. Then again my ears don't work as goods as they should, so I might not be hearing it.
We'll see.
 

kpic

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I de-carbonize the bass boat. :D

However, I really, really doubt I would do it to the Corvette. :L
 

c4c5specialist

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Nope, but someday.
Factors affect results of intake valve deposits

HI there,

Lets talk about this in more simple terms.

Intake valve deposits come from DIFFERENT factors that come together in a perfect storm.

These factors include, but are NOT limited to, oil quality, fuel quality, PCV SYSTEM FUNCTION, adjustable camshaft phasing, camshaft profile, engine oil windage and temperatures.

Washing down backs of the valves with chemicals can repair your issue, but mostly, this is the one downside to the system of SIDI or spark ignited direct fuel injection.

So with that in mind, a truck generation 5 small block has different breathing, different camshaft and different cylinder heads than Corvette to change how the engine breaths and creates carbon deposits.

Normally, using a Borescope, you will find deposits on ALL intake valves with SIDI. The key is, DO THE DEPOSITS CAUSE A RUNNING CONCERN? Its all on what you see.

Do you have a check engine light? Does the engine run rough when you first start it after sitting over night??? Do you notice any type of powerloss? These symptoms MAY or MAY NOT be related to carbon buildup within the intake port area.

Normally, I will inspect every 15000 miles to ensure problem free running.

Otherwise, I suggest cleaning the induction system every 20000 by fogging the intake system with 88861803 Upper intake and combustion system cleaner. It works well and dissolves most deposits without the need for heavy engine disassembly to clean valves.

Allthebest, Paul
 

elegant

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Thank you c4c5specialist. Always value your posts, and will follow this recommendation on my LT4.

Thanks again Paul!
 

JOV

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Paul ,

Great advice but I cannot believe GM does not have a recommended service procedure to address this issue every so many miles in the maintenance schedule to keep the LT1 and LT4
in top running condition. I would figure when GM does a new design they incorporate a service procedure and TSB for a specific problem. So now if coking on my intake valves is the reason for a bad running condition that GM would replace both heads and valve assembly's Under warranty . To me if the intake valves were coked so bad to cause a bad running condition, using GM Engine Top Cleaner I think would be just a band aid for a temporary fix and what would be really needed is removal of the intake manifold and de-carbon the valves with a high pressure cleaning procedure. Does GM even have a TSB to address the valve coking ??? Just my $.02 and glad that my 2015 Z06 has the 5year / 100K mile power train warranty. :thumb

Anyway Thanks for your explanation very much appreciated and that's why I love this forum !! :beer
 

c4c5specialist

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Nope, but someday.
HI there,

Normally, I will use OTC 7448 canister to pressurize the cleaner and fog the system while the engine is running.

Pressure is over 65 psi to enable finer atomization to get the cleaner to the backs of the valves. I have used a number of different cleaners to attempt to find one that really is superior over the others, but the GM cleaner I have used seems to be just as good, if not better than others on the market.

It is very difficult to determine effectiveness without accurate measurement of carbon deposits both before and after.

One very important part is to understand that when you fog a system, you are creating different fuel trims and those compensations of the engine control system must be reset AFTER you do a cleaning.

JOV, Honestly, this condition on Generation 5 small blocks is so far lower than on the overhead cam SIDI engines that use different cam phasing technology to increase exhaust reversion into the intake port area. This is a much different system with a fixed camshaft lobe overlap. I truthfully believe time will tell as far as how our Gen 5 small blocks do over time.

Allthebest, Paul
 
Last edited:

JOV

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2019 ZR1 Blade Silver Metalic
Paul
C4 C5 Specialist


Its guys like you that make this forum great !!

"YOU DA MAN " !!!! :thumb:thumb:thumb
 

gaC5

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Direct Injection Intale Valve Coking

Good advice.
Do you have a specific procedure/tools you use?

I put a catch can on my 2014. It catches the oil that bypasses the pcv valve and cokes your engine.
 

kpic

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HI there,
These factors include, but are NOT limited to, oil quality, fuel quality, PCV SYSTEM FUNCTION, adjustable camshaft phasing, camshaft profile, engine oil windage and temperatures.
Allthebest, Paul

What do you mean by engine oil windage?

I'm familiar with windage trays in the oil pan which prevent oil splash from hitting the rotating components.

The better designed windage trays have blind (louver style) drains which lack a line of sight for pan oil to "splash" on the crank. Yet, support fast drainage from the rods.




 

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