What type of crud did they find? Debris or other liquids (e.g. water)? Large debris should get blocked by the filters, very fine debris can get past the filters. And then it'll flow into all 6 injectors too and thus such debris is not going to affect 2 specific cylinders... it's either all of them or none of them.
Water or other liquid contamination can cause deposits to accumulate in the fuel injectors and, like hardening of arteries in the human body, such build-ups will occur at different rates in the various injectors. So 2 could be built up enough to cause fuel flow issues while the other 4 are not quite so bad... but they'll still have some buildup and won't be working 100% correctly either. Normally, when an injector is partially plugged the vehicle
a) suffers power loss at high speeds or when accelerating hard --> because a partially blocked injector can't spray enough fuel.
b) may have a rough idle because a partially blocked injector has a lousy shaped spray pattern... so the fuel isn't properly distributed inside the cylinder. At medium engine speeds the airflow inside the cylinder helps to "stir the mix." Idle though has very low airflow rates.
Easy to self-test the gas tank for fluid contamination: you need a gas rated siphon pump and a glass jar. Fill the jar about 3/4s full of gas and let it sit (outside!) in the shade for an hour or so, covered. Then look at it. If the gas has water or other liquid contamination you'll see layers as the fluids separate. A mechanically inclined person can park the car on a level surface and disassemble stuff to get to the top of the fuel tank... then by removing the fuel pump or the fuel level sensor one can literally see into the tank. Let it sit a while, then shine a flashlight into the tank to eyeball the gas and condition of the tank. Water contamination will be visible, as will rust buildup on the inside of the tank or other physical debris.
Are cylinders 3 and 6 the two rear-most cylinders (closest to the firewall/passenger compartment) on the Genesis? I don't know Hyundai's numbering scheme on the V6s... many cars often suffer oil buildup issues on the rear-most cylinders simply because the engine is often tipped backwards (mounted that way to line up with the driveshaft, and parking in sloped driveways tips the whole car, adding to that). When the
valve stem seals wear out (they keep oil that flows loosely in the cylinder heads from flowing down the valves and into the piston cylinder chambers) oil can get into the cylinders when the vehicle is shut off. That can lead to a bit of tailpipe smoke at startup and a lumpy start-up idle. Very common on engines with 50K+ miles... it's normal wear.
mike c.
