Jeremiah_350z

Ok so I have a 2006 Nissan 350z rev up and I installed a tomie ti exhaust and the air and fuel ratio was bad and I needed a tune so I went up to dynasty to get it tuned and they had to pause the tune because my car was misfiring bad so they replaced the spark plugs and coil packs and that fixed it a little bit so they put it back on the dyno for 1-2 minutes and then checked cylinder 4 spark plug and it had a little bit of oil in the cylinder and a little bit of oil on the end of the spark plug and we did a compression test and all cylinders are at 180-190 but cylinder 4 was at 165 does anyone have any idea what could cause the loss of power and cause this to happen or has anyone had any similar problems like this?

Ponyryd

Well if it went lean it could have easily burned a piston, broke a ring land, etc…An exhaust alone should not have caused that failure.

dkmura

iTrader: (64)

You don't mention how many miles were on your Z, but depending on use and maintenance there are many possibilities. Installing an exhaust properly will not cause the air/fuel ratio to be altered significantly.

Jeremiah_350z

no I don’t think it was the exhaust that did that because it was about 2-3 months after I installed the exhaust I’ve asked several people and they either said it could be the valve cover gasket or valve cover stems or piston ring or a piston and told me to ask on here also the car has only 123k miles on it

Jeremiah_350z

it has 123k miles on it and I don’t believe it was from me installing the exhaust because 2-3 months I was good and then it started misfiring my tuner said that the exhaust and the cold air intake is pushing too much fuel and I do need a time but I don’t know I just was praying that I didn’t blow a cylinder with the oil getting in the cylinder somehow

Ponyryd

Valve cover won’t let oil into the cylinder, valve seals might, but won’t affect compression at all. Piston ring or piston would be my guess, and after reading the post above it sounds like you may need a new tuner as I highly doubt a cold air and exhaust would cause a misfire, and would not require a tune afterwards.
This might need to be looked at by a pro, but my first step would be pulling that plug, getting the piston to the bottom of the cylinder and taking a look inside with a boroscope. And scratches seen on the cylinder wall, or any part of the top of the piston that appears to be missing is a huge problem.