[e82_n55_]

Specs: 2013 135i N55 DCT (stock) 60k miles

Short version:

- WOT at high elevation
- Limp mode
- 3 cylinders misfiring
- 1 injector stuck open
- Replaced injector
- No codes or check engine light but…
- Loss of power and acceleration (roughly 20% less)
- Sounds like shit on cold start
- Replaced spark plugs and ignition coils but didn’t change anything
- What could it possibly be?

Symptoms
- Slow/sluggish acceleration
- Reduced horsepower and torque
- Rough idle (louder than usual too)
- Hesitant cold start (not smooth at all, like it can’t breathe)

Long version:

Backstory: Drove up to the mountains (up to 6000 ft high), kept it under 4k rpm the whole way up but as I approach the top I saw a long road and went WOT, as soon as the car was about to hit redline and shift, I got a message: “Engine Malfunction, Reduced Power” and had to drive an hour down the mountain to get cell service while in limp mode. White smoke was coming out the exhaust for 10-15 seconds when I initially started driving back down. When accelerating from a dead stop, the engine was shaking/stuttering and I started hearing a ticking sound coming from the engine under load. Engine smoothed out and no more ticking sound when cruising (not accelerating) around 1.5k rpm. Oil temps were lower than usual but nothing overheated.

Took it to the mechanic, he checked the codes and apparently I had 3 out of 6 cylinders misfiring. Turns out it was a leaking injector and so I had them replace it and recode it.
That “fixed” the issue, there was no check engine light or codes popping up, but the car sounded horrible when starting it up. It was very hesitant and rough on a cold start and I could immediately tell that there’s something wrong.

When I started driving it, I could immediately feel a loss of power and acceleration (about 20% loss). It didn’t react as soon as my foot pushed the pedal and overall it feels like there’s back pressure or something is not working 100%.
I replaced all the spark plugs and ignition coils but that didn’t fix the issue. Did a compression test on all cylinders, came back fine.

Here are my thoughts:
- Could I have damaged or clogged my catalytic converter when it was dumping raw unburnt fuel onto it? (causing the white smoke)
- Could an injector from 1 of the other 2 cylinders that were misfiring be damaged from the misfires? (not the injector that was replaced)
- Could it be HPFP?

What could be causing the reduced power?
Any help is appreciated, thanks!