997Yoshi

I recently bought a 2007 997.1 C4S that upon delivery developed a check engine light with the following codes:
In response to this I installed new coil packs and spark plugs.

I noticed the previous owner had swapped coil packs around from their original locations in an attempt to point the finger at faulty coil packs, as each of the numbers didn't match the correct cylinder.


New coil packs and plugs installed, supplied by our friends over at Pelican parts.

997Yoshi

Initially the car ran noticeably better/smoother, then the following day the check engine light came back on with a familiar misfire.


With the same fault codes.

This is where admittedly i am in over my head.I also got a P0420 code.



So i ran some live data with the engine running and obtained the following variations in Oxygen sensor voltage that was completely in sync with obvious misfires.





I also should mention that i can stop or reset the misfire by shutting down the engine and restarting. I also have a noticeable rattle coming from the right hand Porsche Sports Exhaust.
Anyone with any knowledge or experience please chime in! I am thinking i have a bad catalytic converter and possibly bad oxygen sensors? Would this cause the above mentioned symptoms?
HELP !!!

Petza914

I think you've solved your own problem. A rattling cat isn't functioning correctly as the platinum material inside is broken so no longer effective and this is why the misfires are all on one bank. Other possibility is a vacuum leak on the intake to that same bank (manifold or plenum connection) but with a rattling exhaust, most likely the cat.

Bomar Shelby

Check valve lift sensor there are two , one for each bank. I had those codes and symptoms and one was dead. replaced them both $220 each plus 2.5 hours labor. You could just do the one that is dead but then you will be doing another 2.5 hours labor to change the other one in the future.