This is a follow up question to my initial question which can be found here : LTFT and STFT values are off and don't make sense
Car is a 2015 F10 M5 Mods : Cold air intake, aftermarket rear muffler (just section 3).
Since posting the initial question, I have done a lot of research, learned a lot about the car and figured out what the problem was. The problem is, the conclusion I come to makes no sense.
So let me summarize:
- After doing several test drives, I now know that stock M5 from the factory has a 7-10% fuel trim variation between its both banks. I have confirmed this after driving 3 different cars built in different years. All these cars had Bank 1 running up to +10-12% and Bank 2 usually around +2% to 0%. So the issue in my car since day 1 had nothing to do with only one side. Why this is the case, I dont know, but I can speculate. The engine in this car is not symmetrically positioned. In other words, one side is lower than the other side (tilted) and everything is also slightly shifted (probably to make room). Intercoolers, wastegates, etc is all positioned slightly asymmetrical.
- The fuel issue I had was, my car was running -4% and -15% in bank 1 and bank 2. So compared to factory, that is 15% rich which is significant. This issue would happen mostly around idle and low rpms (below 4000). Highway mileage on my car (because you always drive on 7th gear and lowest rpm while cruising) was also impacted where I would barely maintain 19 mpg vs now I can easily keep 23.
- After removing my cold air intake, fuel trims immediately went back to factory values. Now I am getting 10% bank 1 and 0% bank 2.
- I have done multiple factory fuel trim adaptation resets before and after swapping intakes to confirm that none of these values are false positives.
- With factory software ISTA, I see that with my cold air intake, multiplicative mixture adaptation read 0.96 bank 1 and 0.85 bank 2. With stock intake, it reads 1.0 bank 1 and 1.10 bank 2. So i can confirm that my obdii tool and software I use (kiwi and dashcommand) accurately reports these values.
- With factory intake I feel the car has more punch in low rpms (higher low end torque) but significantly less power at higher rpms. Car was pulling much stronger with the cold air intake at high rpm.
So now after all of this, I am puzzled and this is driving me insane. How can a cold air intake cause a rich condition? Arent cold air intakes supposed to cause a lean condition not rich? Is there a plausible explanation to all of this?
Furthermore, is running cold air intake in my case going to have very long term effects? I want to keep this car for another 7-10 years. If the car was running 15% richer compared to stock, isnt that very bad (for injectors, coils, plugs, or just the engine itself) ? Or is this some software hoax somewhere? It is mind boggling to me because a cold air intake should not make a car run 15% rich. That is significant.