Hi,

I have problem with my C63 AMG coupe 2016, 20k miles.

When car is warm in the speed range starting from 2,000 to 2,500 rpm from 3rd gear and in each higher gear the car pulsates, as if it was gently choking. The car has catless downpipes, stage 2 uploaded, and a thermal shield on the turbos. There are no errors in the ECU, the logs are normal and nothing abnormal. The power of the car is normal, only in the range of the above-mentioned revolutions the car behaves unstably. I wonder if the turbos are properly connected and if the hoses are functional, what can be happening.

*****Could be any number of things. If you know how, I would check the wastegate modules and wastegate diaphragms for proper operation with a Mityvac or similar in addition to checking the inlet and outlet hoses to and from the intercoolers and turbos for splits or cracks - splits are *very* common due to thermal cycling as well as wear and tear, etc.. Also, check the turbo impeller blades for damage or excessive shaft or end play. Also the mechanical wastegate hoses (vacuum hoses) for splits or cracks. The wastegate diaphragms can occasionally leak causing turbo bleed down, especially on a car with some years on it but not so many miles. You can check the turbos for leakage using a smoke test, or the old school way with some kind of O2 sensor safe throttle body cleaner around areas of suspected leakage, etc... while monitoring a tach or vacuum gauge, etc... for change in idle rpms, or vac level, etc..

Could also be a transmission issue related to dirty or old fluid, or low fluid. Also not enough line pressure at 3-4 or 4-5 upshift causing slippage or cavitation, damaged clutch pack, burnt or burnished steels, etc.. Wet clutch issues if your car has one, or a torque convertor locking or de-coupling issue, from a sticking or improperly engaging lock up solenoid, etc.. There are various solenoids that control all of this as well as multiple feedback loops that must be checked manually or with more sophisticated scan tools that can energize modules in addition to just reading data...

Could also be coil pack related, or other ignition/fuel issue - pull some spark plugs and analyze porcelines and electrode to get an idea of how the motor itself is doing. Also evap canister issues or purge valves for emissions, etc..

Anyway, a decent mechanic could narrow the problem down pretty quickly with a decent scan tool, and checking the mechanical basics like condition of fluids, levels, spark plug reading, and driving the car a bit, etc..

There's other things it could be, but the above should narrow things down a lot, or outright fix your issue if you find something wrong and correct it. Obviously, check the simplest things first before digging into the car.

Maybe it's something super simple, and you find the problem quickly. If you have the means, download your tune and store it, and re-upload a stock tune and see if your problem goes away. It could be a tuning issue. You can always re-upload the original stage 2 tune if the problem doesn't go away, but *many* issues have been traced down to a tune that worked great in the Summer in hot temps, but colder weather or ethanol laden gasoline blends mess up their fueling as it alters a variety of fuel curve and timing parameters, etc.. and the engine starts pulling timing under load, or something else is amiss that doesn't produce a code, etc.. It's complicated.

Good luck!