So to be honest iam quite surprised with lot of people buying high-end latest cars with DI technology...but do they know what they might be heading for? i came across this thread while researching on web about DI...thought you guys might find it interesting..so the question is...considering the fuel quality of Pakistan and the side affects of this latest technology, is it really reliable to run cars with this technology?...i will post one of the replies from that thread...but i suggest you read through that thread....
they figure out a way to prevent power robbing carbon build up on the valves/intake manifold.
The fuel does not wash over the intake valves, thus oil and other bypass product in the intake manifold that gets recirculated for emissions control sticks to the valves and cools there turning into carbon sludge and then baked on carbon deposits.
One of the biggest reasons I traded my 2007 RS4 in for my GT-R was because of direct injection and the carbon build up. It took that car from an amazing all around all weather high performance luxury sedan and made it a normal S4 with a body kit. Not to mention all the trips to the dealer, the intake manifold replacements(the low/high rpm air tumbler flaps seized due to carbon build up) and having to pay for the carbon cleaning on my dime when I only used the Audi approved oil, Shell V-Power 93 Octane and Audi's own fuel treatment/injector cleaner.
Here are some pictures.
Close ups of the rock hard carbon deposits on the valves/valve stems/valve ports:
Carbon covered intake manifold flaps:
Before many hours of soaking in solvent and plain old elbow grease/scrubbing:
After many hours of soaking in solvent and plain old elbow grease/scrubbing:
(note how there is oil/sludge all over the engine bay from the cleaning proceedure. It's a labor intensive, nasty, messy job)
source: What the GTR really needs - NAGTROC - The Nissan GT-R Owners Club