Hello All
Longtime Lurker posting. G35 coupe 6MT with 88k miles, only major service clutch replacement. Burns oil usual for our cars.

My problem is a bit layered please bare with me.
The start of it. Gas gauge recently became unreliable. I went to start car parked on a slight incline. Would not start. Car read 1/4 tank. I got 2 gl and put in car.
Later the same day. Im waiting for my buddy at his home garage and that morning he offered me gas as he keeps a jersey can full on hand. He also had approx 1 gal in 2 g container. Which I put in my car waiting for him. Skip the minutia and to the point it was contaminated. With what he didn't know was not oil. I drove several blocks the engine misfiring, the service engine light comes on. I turned around and siphoned out both sides of tank 6 gals of gas. Dried both tanks and put in 5 gal fresh and 1/.4 bottle of sea foam. Car is still misfiring. Code 300. Changed oil, spark plugs, replaced the valve cover as its leaking oil into spark 5 also plenum and throttle.body gaskets, Cleaned plenum, throttle body, KN Typhoon intake system and MAF sensor. Still misfiring with 300 general misfire code.
Im going to do a smoke check today. Can someone please advise other steps to problem solve this? Could an ignition boot be bad?
appreciate any help
thank you

 

U sure u didnt mix up the coil wires for cylinder number 4 and 6? The way the wiring is routed it is pretty common for people to mix those up. 4 and 6 are the driver side mid and aft coils.