I have been reading a lot about this problem with direct injection engines. Does anyone know if it is an issue with the LT1 engine or if there is any preventive maintenance to avoid it?

 

Lots of good reading in this thread. Make you own decision afterwards.

https://www.corvetteforum.com/forums...-this-out.html

Ant

 

 

 

i read a lot before I got my September 2013 built C7 Z51 bought months before the first production. Lots written about "coking" as it's called with DI engines from BMW, Ferrari etc. They had DI high performance engines well before the LT1. i also did something about the risk!
Here is a 19 page PDF pic/text re what my reseach showed: http://netwelding.com/Catch_Can.pdf

 

GM has been producing DI engines since 2007 with numbers in the millions. There is no big crowd of people making noise about valve coking with those engines. The big issue with the V6 was timing chain failures. Coking was basically non existent as a complaint. You can worry about it or not worry about it but I suspect GM knows how to build engines that aren't as susceptible to it. Some of those GM engines probably have well over 100K miles on them and still there isn't any news of valve coking. I asked the Corvette Mechanic at the dealership where I take my car for service and asked him if had heard of any valve coking issues with any GM engines (they sell and service the complete GM line) and he hadn't heard of any at their shop.

Bill

 

Thanks. I'm thinking that's a very practical way to approach the issue. If there were many problems with the engines, which are also used in several other cars and SUVs, there would be some bad publicity about the engine.

 

Techron every few 1000 miles

 

Just as fancy vitamins make your urine more expensive, Techron makes your exhaust more expensive.

What do you think it's going to accomplish when it's injected AFTER the deposits? That's the whole point. With port injection the techron is sprayed on the back of the valve in the intake path so it does some good. With DFI, it's shot right at the top of the piston dome.

 

 

I was adding the GM recommended gas additive every oil change as it outlined in the Owner's Manual. Now they changed the part number, don't list it and say buy at the dealer! The Owner's Manual says to use it IF you don't use Top Tier.

I use Top Tier ~half the time BUT Sam's Club non Top Tier the other half. Just checked the Net and Sam's 93 octane is $2.89/gallon and Shell, where I buy because it is the lowest and near buy is $3.44/gallon. It's typically ~$0.50/gallon cheaper. I checked the SDS sheets and the GM and Techron look to be the same, same bottle shape as well. Probably repackaged Techron!

I use it "mostly" to avoid sulfur deposits on the fuel sender! Never thought about it before BUT with the C7 to fix a fuel sender the whole rear drive train needs to be removed! Even when on warranty, don't want a dealer removing my rear drive-train! A forum member posted he was horrified when he saw his drive-train on the dealer's floor! Another said the dealer put in two bottles of the GM "gas additive" and his erratic fuel sender reading problem went away. Charged him $100. I recently posted that info when a member said his was acting up and he added a few bottles and all was fine!

Top Tier has nothing to do with sulfur content! It is an additive that can dissolve sulfur. Some crude oil has more than 3% sulfur that is mostly removed in processing. In fact both Techron and the GM product list keeping the sender sulfur free as a benefit. It also can help the injectors clean. Agreed with DI can't do anything for "coking" on the intake valves. .One bottle is cheaper that the 15 gallon difference in price between Shell and Same's Club! (Note we do not have a Costco which is Top Tier.) I plan on using a bottle between oil changes as well!

 

Don't know if it helps but I run Gumout direct injection cleaner or Seafoam DI cleaner about every 500-1000 miles. It seem to run stronger after when I run the 1/4 mile at the strip.

 

 

 

With 100k miles on my previous 2010 CTS Wagon 3.6L direct injected V6, coking was never a problem that I ever experienced. Never a timing chain failure either and I used AMSOIL Signature Series 5W30 since the factory fill was replaced at 5k. I believe GM's design for direct injection has solved the problems other makes have had with valve coking.

 

^^^
Hmm, and what is their magic design?? I was collecting ~1 oz of oil/1000 miles in a catch can in my Z51 that would have gone past the hot intake valves. Some of that would have baked on those hot intake valves. How much have no idea BUT it's what Tadge said is "only cosmetic!" He didn't say it was miraculously better. This is a quote from his Forum post:

"Granted, deposit formation on SIDI engine intake valves is greater than what is seen with PFI engines, but the Gen 5 engines a.re typical for SIDI engines, and in fact better than other SIDI engines we have benchmarked, (Note: he did not say which he benchmarked) So the bottom line is that we believe the carbon build up is only an internal cosmetic issue, not anything that will affect customers over the life of their cars."

I agree it has not been reported to cause a significant performance issue. However like some Vette owner's are paranoid and OCD about fingerprints on their car, those of us who have assembled engines, like the CNC ported heads in the 502 cid Chevy crate engine in my Street Rod and heads on NASCAR engines at Richard Petty's shop etc, I would not say they "solved the problem."

Others, like Toyota have engines that use both Port Injection and DI. The ZR1 has the same, but activated when max power is needed. Would not be surprized if the C8 engine has both! That is what I would call "solving the issue!"

Granted have that same "Catch Can" on my Grand Sport and GM spent a lot of effort for that "no problem" coking issue and have reduced what I am collecting to ~1/2 once/1000 miles. Bet they did not spend that time and engineering effort on a newer dry sump design for a non-problem! I do appreciate what they have accomplished with a low cost system compared to issues with early BMW DI engines that required walnut shell blasting!

 

 

 

Thanks for the Pics. I agree they did a good job but it's not a "none issue." If it was a "none issue" they would not have spent the time and engineering effort to improve the PCV system with lines going from the dry sump take to both valve covers another to the auxiliary dry sump tank and who knows what's inside the block. I collected about 10 oz in 10,000 miles in my 2014 Z51. Now collecting ~half that amount in my Grand Sport with the new PCV system. Although the short PCV hose and valve are in the same location in the Grand Sport as my 2014 Z51..

Now we need pics of someone who didn't have a can!