When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I've seen some threads where owners show the buildup on the valves but has anyone actually had any problems from it (e.g. engine stumbling, codes etc.)?
Yes, here we go again. We have multiple owners w/ over 70K miles on their C7s, and one owner w/ 130K miles, and no reported issues associated w/ valve coking on the LT1.
I've seen no pictures on this forum demonstrating valve coking on LT1 valves, or problems associated w/ same. Yes, other manufacturers, most notably Audi, BMW, and VW were prone to valve coking problems on their first-gen, GDI engines, but I believe design changes have been made largely alleviating those problems. There's no evidence of a problem on either the LT1 or LT4.
My dealer says they have seen some driveability problems on earlier trucks with DI, but I have not heard of any problems on the Stingray.
They usually take the least invasive method of circulating cleaner through the PCV system before doing any mechanical cleaning.
If you would like to read and worry about it a little, here is a good link
I've seen some threads where owners show the buildup on the valves but has anyone actually had any problems from it (e.g. engine stumbling, codes etc.)?
This is an interesting subject that often comes up about adding a "Catch Can" or not! I believe in having a good defense BEFORE I encounter the problem and DON'T believe GM has any "magic solution" to DI issues!
I had collected about 1 oz of "stuff" in a catch can/1000 miles (as have many others) in my September 2013 built Z51 and transferred the catch can to my Grand Sport (which may in fact have a better PCV system-we'll see.) I am waiting to see just what the internals of a LT1/4 look like after some significant miles but until then I'll use the best defense possible!
This is an old post with I made with my reasons:
“Here are two statements re “coking.” One is from Tadge and the second from a published article that was written after the author who spent two days with the Assistant Chief Engineer for Small Block Chevy’s:
TADGE from Corvette Forum Answer: The continuous flow of clean air and gas (in a port injected engine like in the C6) over the intake valve tends to keep it very clean… appreciation of that characteristic is limited to those who disassemble their engines.
“…we did extensive testing to make sure there were no customer-observable penalties (in the LT1, DI engine.) We have not seen anything unusual… Granted, deposit formation on SIDI engine intake valves is greater than what is seen with PFI engines…”.
(Side Note: I assembled an Olds engine I put in my first car a '41 Coupe with new shinny valves and polished ports. More recently I assembled the 8.2 Liter BB I have in my Street Rod-I liked the clean shinny valves and CNC ports and matched manifold and will not be happy with baked oil on the backs, even if just cosmetic!)
In an article written by Brian Gillogly who spent two days with John Rydzweski, Assistant Chief Engineer for Small Block V 8’s discussing the LT4 and Jordan Lee, both work in small block development. It states: “A little bit of oil on a port-injection engine can help lubricate valves, but because the Gen 5 V8’s (all C7’s as the LT1) are Direct Injected, there’s no fuel washing the back of the intake valve. That means oil in the PCV system can end up sticking to the back of the hot intake valves impeding airflow and eventually preventing the valves from seating properly.”
(Side Note: That post was published in the Tech Section and I was criticized indicating it could not came from John Rydzweski as "He would not say that!" Perhaps he would not directly in print because he likes his job BUT I emailed the Author, Brian Gillogly and asked about that specific comment! He said, "That subject came up and the information you quoted came directly from those conversations!")
Hmm, I don't sell the stuff and use my own logic! Considering all the money I spend on mods the ~$175 I spent on a quality catch can is trivial!
That 1 oz/1000 mile of stuff I collect, mostly oil residue, would go past the valves. Some would bake. Doubt there is that much more going through the PVC system or I'd be adding oil between changes!
And what do the engineers in charge of the small block Chevy engine program know who made that comment??? However, I'll accept their knowledge!
Guess I could revert to the "road draft tube" I had on my '56 small block and avoid anything going from the crackcase to the intake manifold and just dump it on the ground!
If that comment attributed to info from the Chevy engineers for small block engines happened, i.e. a piece of carbon caught on the edge of an intake valve, it would cause detectable issues, like a slight stumble or miss.
But expect with just a collection of baked on "stuff" on the intake valve backs will cause mostly just decreased power, many would not detect.
However performance engine designers work hard to contour the back of the intake valves to get high flow. Baking on carbon deposits (coking) reduces the flow and max power.
Below is a pic from the 8.2 Liter engine I assembled for my Street Rod. Don't have a pic of the back of the valves, only the front. However when new they looked just as shinny as did the intake passages (shown in top pic.) A very thin film of black carbon is expected but NOT lumps of the stuff! In my case, that 850 Holley Double Pumper runs rich and gasoline washes the back of the intake valves. With DI only air and a very small amount of gas that can enter the valve when it is slightly open before the gas squirts directly into the cylinder contacts the back of the valves.
We do need to see what the insides look like when someone takes one part with lots of miles!
8.2 Liter ZZ502 Big Block. That small round item on the second from right cylinder is a quarter! Intake ports as well as the manifold are CNC ported.
If you Google the subject the one thing you find is GM in general doesn't have an issue with valve coking on any of their direct injection engines. The number of complaints is so far down in the noise level that it doesn't make a big impression compared to the issues with the VW engines. GM has several million DI engines on the road so if there was a problem it would be well known. The catch can is a solution looking for a problem.
Hope that statistic is better than what forum posters think about Tadge's last post saying their statistics show "no problem with Z06/Grand Sport wheels cracking!"
I look at it this way, I followed the Any Grove philosophy outlined in his book "Only the Paranoid Survive!" In fact have followed it all my business life well before the book and done very well (but not as good as Andy! )
I'm prepared when the worse occasionally happens -which it occasionally does. For $175 a catch can is cheap insurance, IMO. Some of that 1 oz/1000 miles of "stuff," mostly oil, I collected in my C7 Z51 would have baked on the intake valves. We'll see what it is on my Grand Sport which has a "better" PCV system.
Thinking GM has some kind of magic to prevent "Coking" with DI reminds me of Joe Pesci's comment in my Cousin Vinny:
I'm curious; what symptoms would present? Hesitation?, mpg getting worse?, funny sounds/feel?, more noticeable oil consumption?...
Lisa, we can use yours as a great example that the DI engines of today are quite reliable. At 77K on yours without any noticeable problems (I take it by your question you don't have any), we can safely assume if there was any you would have them by now.
Last edited by Rebel Yell; 10-30-2017 at 01:19 PM.
I had over 70K on my 2008 Cadillac CTS when I traded it in in 2014 and it had a first generation 3.6L DI engine. Fuel mileage was identical to what it was when the car was new and there was no perceptible loss of power and certainly no rough running outside of the annoying initial cold start "idle searching" that it had from the beginning.
As Bill noted, coking was a big problem with a number of VW engines and the early BMW DI engines were even worse but it has not been an issue with GM offerings.
But I wouldn't be surprised to see GM introducing some combined port + DI injected engines in the future like some of those coming from Asia. If this hybrid injection system reduces the particulate matter generation it may help prevent the requirement of exhaust particulate filters for DI gasoline engines or particulate regulations may just speed the transition to electric.
As Bill noted, coking was a big problem with a number of VW engines and the early BMW DI engines were even worse but it has not been an issue with GM offerings.
Flip that.
It was early VW engines and actually later (recent) BMW engines such as the N54 and N55.
Ford has some issues with it as well on their recent ecoboost engines.
Nothing really about GM DI engines as of yet.
FYI, run high quality name brand detergent fuels from the likes of Shell, Chevron and Exxon to help combat any potential buildup problems.
But I wouldn't be surprised to see GM introducing some combined port + DI injected engines in the future like some of those coming from Asia. If this hybrid injection system reduces the particulate matter generation it may help prevent the requirement of exhaust particulate filters for DI gasoline engines or particulate regulations may just speed the transition to electric.
Not only Toyota and some others but the new Ford GT, 3.5 Liter twin turbo at 647 hp has both DI and Port Injection! My guess is when the mid engine Chevy comes out it will be small cid and similar power with both DI and Port Injection. Then there will be some gas with cleaning additives (Top Tier) to get the PVC “stuff” off the back of the intake valves before it has a chance to bake on!
However the GM Marking folks are "smarter" and would have told engineering to run another dyno test and find 3 more HP! How can anyone publish 647 hp!
Interesting. Thanks. Ferrari said they were going to recommend a cleaning fluid drip at each oil change but then I saw that after the PCV oil is baked on, only mechanical blasting (walnut shells etc, was effective.)
CRC is a good company and $16 cheap.
This is what it states: Delivers concentrated advanced Cozol® technology directly to the backs of intake valves
Dissolves baked-on carbon deposits
Improves MPG
Increases power and reduces rough idle Effective for use on GDI and standard PFI engines
The 17 customer reviews were interesting. 88% 5 Star!
Fellow with a Camaro showed before and after borescope pics (although result was not very compelling.)
Thought this comment was interesting: "We are an automotive shop and have been using walnut shell blasting to clean carbon off the intake valves on DI cars. We tried this stuff on our last car and pre-soaked the carbon deposits before blasting - The carbon came off much easier. Instructions on the can say to spray into the intake while running, but I am not sure I would try that. Overall a cost effective way to reduce the use of walnut shell for a thorough cleaning of intake vales for Direct Gasoline Injection valve problem cars"
One response said be sure you have the right area and time, so it may be slow, controlled addition.
10-30-2017, 08:11 AM
Direct injection valve coking
Not only Toyota and some others but the new Ford GT, 3.5 Liter twin turbo at 647 hp has both DI and Port Injection! My guess is when the mid engine Chevy comes out it will be small cid and similar power with both DI and Port Injection. Then there will be some gas with cleaning additives (Top Tier) to get the PVC “stuff” off the back of the intake valves before it has a chance to bake on!