DIY: Downpipe (DP) installation for E90 335i (4/4)
Install the new DP's
19. Comparison shot of the old and new.
20. Take both clamp connectors and loosely place them on the turbos
21. Connect and tighten the REAR O2 sensors.
22. Position the “rear” downpipe and “hook” the clamp connector into its final position.
23. Align the hanger bracket – note the notch and the holes. This is the “critical” connection to have aligned, since the fitment to the cat-back is dependent on this. Inset the smaller of the bolts included in the kit into the hole and hand tighten the nut.
24. Now go back to the turbo, and thread the bolt back into the rear clamp connector. Make sure the orientation of the clamp connector is in the same position as it was taken off (refer to the picture for step 13). This will ensure that you can do the final “clamp down” with the wrench. Install the front “rear” O2 sensor and tighten.
25. Install the other “front” DP in the same manner as the rear. Since all connections are still loose, this should be an easy process. This picture shows what everything should look like, right before you insert the bolt into the front DP clamp connector. DO NOT tighten either of the clamp connectors yet!
26. Using some pressure and 2 13mm wrenches, “push to seat, hold, and torque” the hanger bolts into position for both DP's. These are the first 2 bolts to tighten down completely. Now look at the end of the DP's and they should look just like this picture – aligned to the catback!
27. Re-use the gaskets from the uninstall, and loosely attach the muffler.
28. Go back to the turbos and tighten the rear and front clamp connectors. Reinstall and tighten the front O2 sensor (not shown in picture).
29. Using 2 13mm wrenches, tighten the DP bolts at the catback connection. (no photo). ALL FITTINGS SHOULD BE TIGHT NOW!
30. Ensure that all O2 wiring clips are back in place.
(No more pictures from this point)
31. Reinstall the muffler bracket in the rear.
32. Reinstall the heat shield. Do the 2 “PITA” bolts first. Rotate the steering rack back into its correct position and reinstall the third bolt.
33. Reinstall the steering rack. Remember to tighten BOTH sides.
34. Reinstall the hose mount. At this point (and no earlier) you can opt to test drive the car to make sure everything is good. Listen for exhaust leaks, etc.
35. Reinstall the 2 hanging brackets.
36. Reinstall the the engine cover. Congratulations!