I recently passed break-in period for my 2020 C63s so I was testing some hard pulls on freeway today in low gears.

While driving in Sport+ mode with manual shifting, I experienced what felt like fuel cut off during acceleration making the accelerator pedal and engine non-responsive for about a second or two.

I am still getting used to this car so I might have pressed upshift gear too late. I just want to make sure what I experienced today is normal behavior for this car.
At what rpm is fuel cut supposed to happen?

 

7200 is way past where you should be shifting ... you are actually losing power at that point and going slower

 

Yes, there is a rev limiter and it will cut fuel if you run into it. It's somewhat soft, though. It's like the power dies at the top and the car stops accelerating. My previous cars had much more violent rev limiters, which would cut the fuel, then the revs dropped and it started to inject fuel again just for the revs to run into the limiter again, so you were literally bouncing off the limiter. In this car it just holds the revs at the limiter and stops accelerating, so it's not bouncing. You basically have a moment of zero acceleration until you finally shift. I honestly don't know exactly where it comes in, because I go by the shift lights. If you have the digital instrument cluster, once it flashes red, you have about 1 second to shift or you'll run into the limiter. I do occasionally run into it if I'm focusing on what's going on ahead of me, and my reflex isn't kicking in fast enough. Note the limiter and shift lights are only active if you put the transmission in M. If you just use the paddles, that will activate temporary manual mode, and in that mode it will upshift automatically if you miss the shift.

 

Yes, but v8 sounds so good at higher rpm compare to my previous I6 turbo M3 so I just wanted to hear more of that

Thank you for the detailed explanation. Next time I use manual shifting, I will change HUD to show rev meter so that it is easier to be aware.

 

FYI - redline is 7000 rpm (not 7200). Anything above 7000 rpm, you will hit a soft limiter/fuel cut. The TCU/ECU won’t allow for it in the M177.

 

Thank you for the clarification. No wonder I felt surprised with fuel cut yesterday since I did not feel like I reached 7200 rpm yet and still got fuel cut.

 

Hey guys, im from the m156 c63 forums, and been dealing with this fuel cut issue for a year. Just saw this thread and hoping someone shines a light.

I have a 4L blower on a m156. 900cc injectors. No upgraded fuel pump. But the pressure does dip down to 20 psi at pst at times otherwise stays 40+ psi. That said, others with the 4L blower, not having issues at all, just me.

Symptoms: car goes to redline if acceleration is, say, about 80% or less. However, when the car detects WOT, it will go all the way upto and usually, 6000rpms, and a hard stop (as if it hit a limiter of some sort), while it stays at 6k for 2 to 3 seconds (not bouncing off this fake limiter, just can hear engine/exhaust at much lighter tone and consistent), then followed by a fuel cut according to hp tuners, assuming ecu is trying to save the car at that point. If you still have it floored while the fuel cut happens, it re-engages to accelerate but hits the same "limiter". If i slowly accelerate past 6000 rpms, and then WOT it, the rpms cuts out right at the current rpm i punched the pedal. Sometimes happens at 5500rpms, few times happened at 6500rpms. Redline is 7200 on the m156, never had issues when it was NA setup.

Seems to happen consistently in all gears. Lower gears it seems to happen around 5500rpms. I think it all depends on how you "get into it" initially with the accelerator and then the rpm cut will cutout accordingly..any advice is appreciated. Im dumping tons of money on diagnostkca and getting no where. The supercharger should be making 7 psi in current setup. Also, not getting any codes, xentry not showing anything either. I swapped throttle bodies, swapped out accelerator pedal, im lost at this point.. bleh. Sorry for a novel.

 

*****Sounds like a fueling problem. How many miles on the car and have the fuel filter(s) been changed? Slightly clogged fuel filters or dirty filters will limit fuel flow of pump through peripheral resistance. It's possible the pump itself is going bad but replacing the filters is cheaper and easier thing to do. I don't know what the stock size injectors are on your car but 900cc injectors are not small injectors. 900cc are about 85lbs/hr injectors which can move some fuel with adequate pump and proper injector duty cycle. Electric fuel pumps can lose efficiency over time and not flow rated capacity - this can be checked of course.

Ideally, a dyno with AFR and EGT readings could spot this type of problem, or at least narrow it down a bit. On other platforms, every psi of boost will bring up fuel pressure in a linear manner - perhaps 1psi per lbs boost depending upon the fuel regulator. I'm going to assume your car is tuned and the injector duty cycles are setup for your car and not for stock injectors or something else.

Anyway, I'd check fuel filters and then fuel pressure regulator, and fuel pump output, especially for a non stock setup. Better to have too much fuel pump properly regulated to insure adequate pressure and volume vs the pump not able to deliver the fuel at higher boost levels and you cook your motor.

Good luck,

 

I appreciate the response. Yeah, i have been dragging this. I did get a fuel filter for my coupe. Assuming thebfilter is behind driver side (under the rear seat on driver side).

My fuel pressure at WOT is anywhere between high 40s to mid 50s psi. And at idle and normal driving 60 psi or so.
No CEL regarding fuelling or anything...but...lets see.

yeah its all tuned properly. Went through few reputable tuners, but all same issue. Definitely not the tune or injectors. Had 1200 cc injectors but then downsized to 900cc flow matched injectors (theyre oem injectors flowmatched for 900cc, so no splicing of connectors...all oem fittings). Lets see...hoping to have er done by summer.....

Thanks again eh