I genuinely think there is nothing that can be done to prevent this from happening outside of a design change. I had a 2006 passat that was DI and turbo and they were known for misfires from carbon build up. People tried catch cans, water/meth injection, chemicals, additives, and nothing touches it. The fix was pulling the intake and either scraping off the carbon or media blasting it. I have not seen this on any Nissan yet, but I have definitely seen build up on a Hike that had like 10k miles on it. No running issues at all though.
Companies have come up with shop solutions to help with this that, from what I've seen, all are a media blast set up of some sort.
I can't recall off hand what the fuel rail set up is like on a PF with DI to know how something would be installed. I haven't messed with them much at all, really. I do know that I never recommend any of those induction services myself. My shops have some set up that injects a strong solvent into the intake to do some cleaning. I only have experience with two styles. One connects directly to the valve on the fuel rail, if the car has one, and the chemical actually replaces fuel and runs while it cleans. You know it's done when the car starts sputtering. The other has a spray nozzle with a flexible aluminum tube that you put somewhere in the ducting aiming at the throttle body, after the MAF sensor. It uses shop air to spray a mist out. I hate this style. I'm pretty sure I wrecked an engine at a shop I worked at using one a few years ago. It's hard to tell exactly where the spray is going and can it just pool up. As soon as you start going, WOT or not, the engine can take a big chug all at once. I've read articles where engines have been hydrolocked with this style if there is a tumbler valve in the intake that just collects it and dumps it all at once.
Very reputable professional publications recommend them every 15-20k miles on DI engines, but I just personally haven't seen any evidence that shows that they do much. I believe that they probably clean throttle bodies a bit, since you can watch soot get washed off of them even with cleaner, but that heavy stuff baked on the valves? I don't think so. Dirty throttle body commonly causes p0101 MAF circuit codes.
I'm interested to take a look at a DI next chance I get to see how you might get in there, unless they tapped into the low pressure system and pushed it from there? Maybe there is a kit with a fitting that replaces the pressure sensor to let it in and just runs on a set pressure with that unplugged until you clear the code? I'm not sure.
I think I'd wait until it's time to change the plugs and ask the shop how much more they would charge to clean the valves up while they have the intake off. I'm not sure that carbon in the top of the pistons would be from direct injection. That sounds like more of an oil consumption problem to me. Are you losing oil?
Sorry to George, I misread your question a while back about recommended set ups. I'd just get a cheap bluetooth obd2 dongle and download torque pro for $5. It works well enough for me and can do as much as any other obd2 scanner. And you're right, timing would be pulled if pinging was detected. You should be able to monitor the knock sensors and timing in the ECM with a scantool to see if this is happening. Timing would show up on that basic set up, but not the knock sensors.
