Hello all!
My name is Steve. I'm 46, live in Portland Or. and I drive a 2018 Honda civic Si 1.5l coupe{lb15Y}. I bought the car in 2018 with only 12 miles on it {7 of which I racked up on the test drive!]. I've always been a Honda boy from the start, with my first car being a '98 civic Ex 4-dr. Then an '04 Accord and then an '07 Si (sedan) and now to my current daily driver. I have 2 teenage offspring...ALL THE TIME!!!! LOL Who I love very much!
Here's the funny thing, I actually came here seeking knowledge and guidance? My car has recently begun acting kinda chitty to me. It randomly set the check engine light and set a P0712 (rich bank 1) due to the minimum fuel trim threshold being crossed on the LTFT (LTFT= -25.00%) Upon investigating I found that my blow by gasses were seriously high. When removing the oil filler cap while vehicle is in idle, the gasses were shooting out, hitting the underside of my hood and blasting me right in the forehead. Now, I couldn't find any info ANYWHERE that had an exact amount of pressure that is allowable for the blowby gasses to be but to me, that seemed a bit excessive? I also found that all around the top of the block, there was oil seeping out the head gasket. Long story not so long, I tore the head off to replace the gasket and found that injector 4 was clogged up for god knows how long and the inside of my INTAKE manifold was full of carbon and unburnt oil/fuel. The EXAUST manifold was clean as a whistle! I think it's supposed to be the other way around right? My biggest issue is I may have slightly modified the car over the years and most of the parts under the hood are aftermarket but my problem is this! This issue that i am having is almost exactly the same issue that other vehicle of the same year, make and model are also displaying and on stock internals!

 

Direct Injection engines like yours do not provide fuel in the intake runners like a port injected engine does... and therefore, no fuel is present to help keep the intake runners and valves clean. Exhaust gas build-up and oil film residue reach this area of the intake tract due to camshaft lobe/valve overlap.

 

What is it that owners do to solve what the poster's talking about?

 

There isn't a great answer... some try additives that break down some of this build up (it would have to be drawn into a running engine through a vacuum port or through the intake tract post intercooler to be effective in the case of a turbocharged engine). Pulling the cylinder head and intake manifold would certainly be a last resort.

All manufacturers are aware of this issue, and if you look at the evolution of DI engines, you will see that some manufacturers have actually updated engines that were DI only to DI and Port Injected designs... and these use very small amounts of fuel delivered by the port fuel injectors to help keep the intake runners and valves cleaner. Unfortunately, Honda hasn't made this step to improve engine life in their current engines as of yet.