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2008 CTS 3.6 RWD LY7, FE2
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Discussion Starter #1
The story starts yesterday, sunday, the family and I went on a little sunday drive to a dairy farm to see some sights and buy some cheese. When we got home I checked the oil and saw it was about 1/4 - 1/2 qt low so I added about that much. This morning I start the car to leave for work and i noticed it had a bit of a misfire after a few seconds. It wasn't bad so i just figured i would drive it and see what happens... short story is that it is now at the dealer for cyl #6 misfire and also multiple misfire (they pulled the codes).

The car would run smooth above 2500rpm out of gear but even at 3000rpm in 4th or 5th on the highway it would buck like crazy. Any gear and any amount of load on the engine would make it go crazy.

The dealer called around 1pm and verified that the coils and plugs are good, asked for the go ahead to do an intake cleaning via some cleaning fluids I agreed but also asked they check the compression on #6. I have not heard anything back today, 5:15pm now. The spark plugs were replaced 7k miles ago and this is a PFI engine. I regularly use top tier as well as seafoam in the fuel in the past.

Does anyone have some experience with this issue? Ideas?
 

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'14 CTS-V LongRoof; '16 ATS-V Sedan,' 04 Trailblazer 4x4; '10 CTS LongRoof gone but never forgotten
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14,181 Posts
Using a liquid to clean out the carbon buildup is a no-go, a ripoff. You don't say how many miles you have driven, but usually the best way to clean the intake is to pull it.
 

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2008 CTS 3.6 RWD LY7, FE2
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55 Posts
Discussion Starter #3
well they say its fixed, had to replace one spark plug (only 7k miles old) along with the intake cleaning. I looked at it and it was completely fouled out, probably from the intake cleaning. Leaving to pick it up now, im glad it is fixed but im skill skeptical that this was the problem. I bought the car at 88k miles last summer and it now has 106,6xx on the clock.

First order of business is to install a catch can...
 

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'14 CTS-V LongRoof; '16 ATS-V Sedan,' 04 Trailblazer 4x4; '10 CTS LongRoof gone but never forgotten
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14,181 Posts
So how much did they pork you?
 

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2008 CTS 3.6 RWD LY7, FE2
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55 Posts
Discussion Starter #5
$208 and change. Better than it could have been I suppose but for essentially a seafoam treatment its one hell of a ripoff! $50 for throttle body cleaning that I had already done about 15k miles ago, $131 for "fuel induction service", and no labor charge for the spark plug replacement, the rest was "shop supplies". On the plus side I did get a drive brand new 2015 cts awd with the 3.6, pretty sweet ride. Not sure I would go awd though...
 

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'14 CTS-V LongRoof; '16 ATS-V Sedan,' 04 Trailblazer 4x4; '10 CTS LongRoof gone but never forgotten
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14,181 Posts
When I took my car in for its 50,000 mile checkup (I was there for my transmission - I wouldn't take it in just for a checkup) the dealer told me it would get a fuel treatment to clean out the carbon on the valves. I told him bulls!t, this is s DI engine and what you are telling me is 100% wrong. He never liked me after that, because he was dead wrong and I called him out on it.
 

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2008 CTS 3.6 RWD LY7, FE2
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55 Posts
Discussion Starter #7
For a DI engine the only thing fuel treatments and top tier are going to do for you is keep the fuel system and the injector clean, but considering the pressure the injector is operating at I wonder how effective it really is.

I think the problem I had was a piece of carbon came lose and got stuck on the seat of the valve causing low compression. A lot of the service guys are really salesman at heart. I am an engineer by trade and an automotive enthusiast so I understand very well what is a gimmick and what is beneficial. A fluid cleaning in the intake can be helpful but the only way to get it honestly clean is by physically removing the carbon/sludge. But again, seafoam and stuff similar is only about $10 a can as compared to the hours and hard work it takes to manually clean the intake and valves.
 

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2008 CTS 3.6L DI AWD
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Dealer just tried that on me- I have DI and they wanted to hookup my fuel injection to flush it.

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For a DI engine the only thing fuel treatments and top tier are going to do for you is keep the fuel system and the injector clean, but considering the pressure the injector is operating at I wonder how effective it really is.
When my injectors were carbon fouled about 2 years/10k mi after I bought my car, the dealer said there was a tech bulletin from cop orate to inform customers to use regular gas from companies that have a high amount of detergent in them to keep the injectors cleaner. Prior I used brand gasoline that refined their own gas and didn't buy from stations where they bought from any supplier. Now using high detergent brand regular gas, no problems since.

My aunt has a 2013 CTS-V, and when she asked her dealer about using specific brands of gas , they said they never heard of such a thing.

My sister has a Hyundai with DI and uses any brand gas and never had issues with her DI
 

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2008 CTS 3.6 RWD LY7, FE2
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Discussion Starter #9
Dealer just tried that on me- I have DI and they wanted to hookup my fuel injection to flush it.

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When my injectors were carbon fouled about 2 years/10k mi after I bought my car, the dealer said there was a tech bulletin from cop orate to inform customers to use regular gas from companies that have a high amount of detergent in them to keep the injectors cleaner. Prior I used brand gasoline that refined their own gas and didn't buy from stations where they bought from any supplier. Now using high detergent brand regular gas, no problems since.

My aunt has a 2013 CTS-V, and when she asked her dealer about using specific brands of gas , they said they never heard of such a thing.

My sister has a Hyundai with DI and uses any brand gas and never had issues with her DI

It's referred to as "top tier" fuel. All gas is refined the same, as of last year there were only 139 refineries operating in the US. You're right about the detergent, top tier distributors are certified to use high quality detergents and in high enough concentration to actually clean the fuel system.

If anyone comes across this and is interested, through this experience and research I have decided that Tech-ron, made by Chevron, is the only fuel additive I will use in my vehicles.
 

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2009 CTS 3.6 LY7
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I use Chevron/Techron as well, never had a fuel injector problem on some high mileage (120K, 150K) vehicles that were otherwise known to have them.
 

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2010 CTS 3.6L V6 RWD Performance
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187 Posts
Very interesting. I had a similar problem last year on a long trip and the dealer claimed it was accidental diesel contamination. I always doubted this as I am always careful about what kind of fuel I add and besides, just how the heck can someone accidentally put in diesel when a diesel pump nozzle won't fit into the fuel spout. My problem was intermittent until finally it continuously misfired and dumped fuel out the exhaust and killed the cat converters. Cost me a couple G's to get it all back to normal. They replaced the cats, cleaned the fuel system, replaced a couple of injectors and plugs. After reading this post I'm more inclined now to think my root cause was the same.
 
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