Concerning about turbo loss
 

I recently felt like my turbo hasn't been as responsive as before but I can't recall precisely what it was like in the past. Maybe the weather is playing a role in turbo performance.
I thought that the boost meter was more punchy before. I have read threads about limp mode, semi limp, software updates...etc but can't tell if this is such situation.

In the past 2 days, I paid more attention to it and the observations, as I remember, are as follows. I tested the sport modes, without putting full throttles in this weather of course.

C43 coupe 2017 stock

Day 1: -7C (19F), very windy, clear road, snow tires
Oil 95C (203F); Gearbox 50-60C (120-140F)
Mode: Sport

Gear: 1 - 3
Throttle: 50%
Revs: between 3000 - 3500rpm
Speed: 20 to 50 kph (12 to 30 mph)
Torque: 150~ lbs pk
HP: between 50 to 100
Boost meter: hovering at 1 bar (the indicator bar), close to 2 bars when peaked

Gear: 4 - 7
Throttle: between 25 to 50%
Revs: between 2500 to 3000rpm
Speed: 50 to 80kph (30 to 50 mph)
Torque: ~100 lbs pk
HP: ~50 pk
Boost meter: between 0 - 1 bars (at higher gears, 0 bars)


Day 2: -9C (16F), light wind, clear road, snow tires
Oil 95C (203F); Gearbox 60-70C (140-160F)
Mode: Sport+

Gear: 1 - 3
Throttle: 75%
​​​​​​​Revs: 4500rpm pk
Speed: 20 to 70 kph (12 to 45 mph)
Torque: 300~ lbs pk
HP: 250 pk
Boost meter: 3 bars pk

Gear: 4 -6
​​​​​​​Throttle: 50%
​​​​​​​Revs: 3500rpm pk
Speed: 70 to 90 kph (45 to 55 mph)
Torque: between 200 to 250 lbs
HP: ~150 pk
Boost meter: 0 - 0.5 bars (when I accelerated again (gear 7?), the torque was quite responsive but boost stayed at 0 bar)

Is the turbo behaving normal like this?
Has HP always been kind of hovering at the low end since I wasn't full throttling it?

I'm still learning the car but got kind of confused or paranoid all of a sudden.

Sounds like a boost leak from somewhere. Definitely not normal. Can you check the piping from the intercooler to the intake?

+1 Sounds like a boost leak. Does it "flatline" as you get on the accelrator? Time to maybe get out some windshield cleaner and start spraying around the engine if its not obviously visual or audible.

I opened the hood and the first thing I noticed was that one side of the air inlet duct was disengaged from the clips, which creates a slight disconnect with the flex hose.
https://cimg1.ibsrv.net/gimg/www.mbw...dc625cc029.jpg
Disconnect between flex hose and inlet duct
https://cimg5.ibsrv.net/gimg/www.mbw...ddfb9c7097.jpg
Dislodged from clips
https://cimg8.ibsrv.net/gimg/www.mbw...df0e8b7861.jpg
Other duct with engaged clips

I tried to snap the duct back to those clips but it was very hard to do. Either there is a tool required for assembly or I'm not strong enough. Didn't want to put too much body weight on it since I don't know what is underneath or should there be a air gasket/debris stuck in between, hence dropped by dealer to have them do it properly. I'm surprised (and not so surprised) that the dealer insists to schedule an appointment for snapping this thing back on at another day...

The decreased pressure on this inlet should be playing a role. Is this small disconnect enough to cause such noticeable drop in boost and sub 100 hp? I'm wondering how the it all ties together (i.e. from throttle to how much air intake goes thru the turbos to how much HP the engine makes at the end)

This is surely the culprit. I'm sure they want the full appointment to fully disassemble and reassemble the intake rather than just leaning on it and hoping it snaps back together.

Just to close this case, I finally got it to the dealer and they rebuttoned up everything. No fault codes but updated the software. The pressure and turbo is back to normal!

I doubt the intake tube going to airbox was the culprit. maybe the code was causing limp mode. my guess is you had a boost leak after the turbo somewhere that they fixed. or maybe uneven air inlet pressure or temp was throwing code causing limp mode. glad its fixed.