This is a follow-up from my initial question which can be found here : LTFT and STFT values are off and don't make sense.
Car : BMW 2015 F10 M5 Modifications : Eisenmann Race Catback Exhaust, MSR Cold Air Intake. Everything else stock.
The summary of my problem is, LTFT values between Bank 1 and 2 are inconsistent where Bank 2 is 10% or more lower (-4% vs -14%) throughout the lower RPM band. At WOT, LTFTs line up and stay equal and behave normally.
Zaid has been incredibly helpful and we narrowed it down to the aftermarket exhaust I have.
Basically there is one big difference between the stock exhaust and the aftermarket one and that is the use of flaps. Each muffler (there are two) has 2 pipes (so 4 pipes total) where 1 pipe on each side has a flap connected to it that is operated by a valve. The valve is connected to a vacuum line. In the stock exhaust, at low RPMs, to reduce noise as well as reduce turbo lag and increase low and torque, the flap is closed increasing the backpressure. Over 3,500 rpm (or around that), the flaps open up. The aftermarket exhausts have no flaps (not just mine but a lot of others) and the standard installation procedure is that they zip tie the vacuum lines and plug them as well (mine has bolts plugged). So in an aftermarket scenario, car operates as if the flaps were always open.
Here is a picture of the eisenmann muffler right next to the stock muffler : https://eisenmannblog.files.wordpress.com/2012/11/8182708317_10988d68b2_h.jpg
Here is a picture of the eisenmann muffler on the car : http://farm9.staticflickr.com/8490/8206133927_6b3bec97bb_b.jpg
The theory we have at the moment is the lack of flaps is causing this rich condition I am seeing. What I don't understand is why this is happening on one side of the exhaust not the other. So far I have done:
- Check both exhausts and where they are clamped, clamps are extremely tight, and there is a good maybe 4-5 inches of stock exhaust inside the aftermarket pipe (after market slips on), so there is no way a leak can happen at the connection points.
- Check the vacuum lines on both sides, they are both zip tied and plugged with a bolt.
- Check the intake installation many times, no air leaks, all clamps are securely fastened.
- Check turbo inlets and charge pipes, no cracks or air leaks.
Returning the exhaust back to stock is not something I want to do. I spent several hours adjusting the tips of the aftermarket exhaust so that all 4 looked identical. Without knowing for sure, I dont want to touch it.
Any help is appreciated.