DIY: Downpipe (DP) installation for E90 335i (3/4)
Removing the downpipes. For reference in this DIY there is a “forward” and a “rear” downpipe referring to the pipes that correspond to the forward and rear 3 cylinders banks.
12. Mark the O2 sensors. Picture shows the front sensors, mark the rear as well. Break the front sensors loose with the 7/8” wrench, then unscrew them by hand. I waited until the pipes were off before removing the rear O2 sensors – easier access.
13. Using the 13mm wrench, loosen the clamp connections for both downpipes. Remove the bolts and set them aside.
14. Moving to the rear of the car, spray the bolts attached to the cat-back generously with liquid wrench or WD40. Let it soak a bit – I have less than 5000 miles on my car and they are pretty rusty. Use a 12mm wrench to remove all 4 bolts.
15. Moving further back, I found it much easier to uninstall the DP's by removing the muffler brace. (Use the E10 Torx socket)
16. Using the 12mm socket, remove the nuts on the hanger for both DP's. This picture shows it fully “uninstalled”, since the downpipes should literally “fall out” now! Notice the rear O2 sensors still installed.
17. Using the 7/8” wrench, remove the rear O2 sensors. (I popped out the brackets – makes it much easier) No picture – see step 16.
18. Your car is now modified with a VERY short 3” exhaust. (I have a video of me starting the car with no exhaust – stupid funny ... LOUD!)