Stumbled upon this TSB. Seems to be (particularly) applicable to direct injection, even though there is no mention of it.

“Subject: Information on Rough Idle, Crank No Start, Extended Crank or Misfire Due to Excessive Carbon on Top of the Valves or Sticking Valves, Malfunction Indicator Light (MIL) Illuminated - DTC P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0307, P0308 Set”

CR makes a kit GM seems to advise against using. I haven’t dared try it yet.

https://static.nhtsa.gov/odi/tsbs/20...37635-9999.pdf

older version, differences are interesting

https://static.nhtsa.gov/odi/tsbs/20...99252-2280.pdf

 

RJ did a nice how to about cleaning the valves in his SS , very informative

https://www.chevyhhr.net/forums/how-...lves-ss-56184/

 

Isn't that exactly a Seafoam treatment?

 

As pointed out , it’s the old Northstar decarbonizing treatment, I did that to my 1988 C1500 in 1999, ended up pulling the heads and cleaned them in the hot tank. Back then it was the valve stem seals that let oil past them to carbonized on the valves and the top of the pistons. In 2005 , I swapped out the 305 for a 350, with modifications.

 

This is not the same issue that we face with our DI engines in the HHR SS. Our problem is caused by crankcase contaminants being deposited on the intake valves by the PCV system.

This is caused by "fuel contamination or incomplete burning of the fuel".

 

The main change I see, is that they don't want to let it soak for 2-3 hours anymore.

 

GM used to have a system for blasting the backs of the valves with crushed shells. Worked good.

 

Right. Notice they say to tell the customer to use Top Tier fuel in the future, so that the better detergent fuel will keep the valves clean. But that won’t help a DI motor. I didn’t investigate whether the Caddy motors mentioned were DI.

Anyway, with piston blowby, boosted by the boost, bumping the crankcase pressure, and oil slingers for piston cooling atomizing the oil in there, there’s a lot of oil-misty crankcase gas to vent, and when it hits hot intake valves, resulting coking is similar if not the exact same thing, and even worse with hard-run tuned motor making 25-30 psi boost, and then throw in a little ring and cylinder wall wear…

(No wonder these guys are hanging catch cans under the hood.)

Asking myself if this should be scheduled maintenance in DI motor, especially a turbo, and especially especially with oil slinger piston cooling.

 

used this a while ago
does not require engine disassembly


surely there are American counterparts

 

Be very cautious about following his Berryman's advice in that writeup. It destroyed all the rubbers components in my engine when it seeped into the oil and contaminated it. I had to rebuild the engine, which I noted at the end of his thread.