2006 XJ8L 4.2. L NA, 225K miles, I got a small leak in the valley coolant hose (again), after I removing the intake manifold I notice what I would consider excessive carbon build-up in the intake passages (I did the best I could with pictures). I don't recall noticing such build-up that last time I was changing that blasted valley hose. I was surprised to see such build up even directly adjacent the injectors. The fuel injector plenums were equally fouled, but I cleaned them before thinking to take photos. I would expect the injectors to wash the area pretty well but as can be seen in the photos there seemed to be very little to no washing by the injectors. So much build -up it seems like a direct injection system. Are these engines known for such build-up? Is the PCV system the main culprit sending too much oil back through the intake? Or do I have bad injectors. How do I prevent this in the future?

 

What I can tell from the photos, the buildup does not seem excessive. As long as the area around the valve and the back of the valves are clean (sort of see clean areas around the valve), it shouldn't be a big issue. Certainly not something I'd worry about past 200k miles. The DI engine issue is when the back of the valves carbon up and restrict airflow.

 

thanks, some of the valves seem better than others...I am hoping I can clear it up with some BG44k....or other cleaners anyone has had luck with in the past. 44k gets pricey for a routine fuel additive.

 

I use both BG 44K and Redline SI-1 in my AJ126 (so GDI), alternating between the two every six months or so.
Of course neither can possibly make any difference to carbon build up in the inlet tracts or on the backs of the inlet valves in a GDI engine but I use them to keep the fuel system and especially the fuel injectors clean. The fuel injectors in this engine (and the AJ133 V8) are known to either clog up from burnt on carbon deposits or fail completely and stick open.
Point is I have done a lot of research into fuel system cleaners, GDI engines and carbon build up, and the general consensus is that the most effective ingredient in any such cleaner is PEA or polyetheramine.
It is difficult to find much info on the net about the respective concentrations of PEA in all the various fuel system cleaners but so far Redline SI-1 has the highest content I have found. It also has a good reputation.
So I suggest that if BG 44K doesn't do the trick for you try some Redline SI-1 instead.

 

You probably need to fit an oil catch can in the breather system. My mate has an Audi v8 that are shocking for getting Carboned up and they need stripping and veining when they get bad.

 

Chevron with Techron, is what i have used in mine.
Two bottles, fill the tank, run keeping the rpm's up.
With manual shifting for the next few drives
Oil catch setup is also a good idea

 

Sounds like an initial treatment of BG or Redline and periodic Chev/Tech treatments going forward, but I can't help but feel like while it's open, I should scrape and chem clean these valves and passages (obviously only when valves are fully seated) I am just not sure it would be worth it and maybe prolonged or at least consistent use of fuel system cleaners will eventually clean it up. I really have not noticed a performance problem, in fact we averaged 29mpg on our trip from Baltimore to Kalamazoo, MI shortly before the coolant hose started leaking. Regarding the catch can, the engine bay is pretty tight, has anyone found a good place for such a can? How would one verify any of these cleaners or cans are working? I won't see these passages again until that blasted valley hose leaks again!

 

The supercharged engines have a filter that catches most blowby oil. It is the intercoolers. So I have not seen issues.
I have a GDI Subaru that can get deposits after only 60 - 100k miles. Regular high rpm driving seems to increase the volume of blowby.
A catch can or AOS should catch a lot of liquids. Reduce the problem.
But after 200,000 miles the buildup looks minimal. A Seafoam treatment should clean if you feel it is needed. Read directions, hose to intake study into Seafoam to hit the back of the intake valves. Would not scrape or use walnut hulls.
Jaguar got DI figured out early. Took Volkswagen a while to sort.