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ENGINEERING THE FUTURE OF PERFORMANCE ™
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M139 43 ECU Tune
    M139 43 ECU Tune
    Purchase M139 43 ECU Tune
    • SKU: M139-43-ECU-Tune

      M139 43 ECU Tune

    • Power gain Up To

      +94 HP

      Torque gain Up To

      +121 TQ

      Advertised gains are estimates of HP and Torque “at the engine” calculated from gains as measured on a Dynojet Dynamometer in ideal conditions and typically show the largest possible change.  Actual gains are dependent on the following: Learn More about Crank HP Vs Wheel HP

      Model – Manufacturers use the same engine in multiple model vehicles and often times they are in a different state of tune, for example: 2008 C63 and a 2008 CLK Black Series.  Both have the same engine, but the C63 has 451hp while the CLK63 has 500hp.  Naturally the C63 will show more gains as it starts at a lower level.

      Model Year – Similar to above, as time progresses, Manufacturers tend to slightly increase power output via software from one year to the next or offer “Performance Packages” with increased power.  The engines remain largely unaltered and as a result, final tuned output remains the same, while the gains are lower as the starting point is now higher.

      Fuel – Fuel quality is HIGHLY important with performance vehicles.  Low quality and/or low octane fuel will greatly impact engine output and potentially even engine health.  Top tier brand premium fuels should always be used to achieve the best results possible.

      Drivetrain – All wheel drive has higher drivetrain losses than rear wheel drive.  This results in lower numbers when testing on a chassis dyno.  Wheel/tire size and weight will also impact chassis dyno results

      Weather/Conditions – Temperature, humidity, altitude, and air density all impact engine performance.  Heat, high humidity, and thin air will all work towards reducing engine output

      Engine Health – Higher miles tends to result in increased build up and lower compression which can and will impact engine output.  Properly maintained engines will have better performance than abused or neglected engines.

      Supporting modifications – The highest power levels require supporting modifications.  Depending on the engine, this could mean forged internals, built transmission, upgraded fuel system, 110+ octane race fuel, etc.
    • Stage:
    • Choose from Recommended Products (Optional):

    • $1,500.00 $1,500.00

    • How To Tune
    • Prop 65 warning
      Warning

      This product can expose you to chemicals including carbon black, silica - crystalline, formaldehyde, and lead which are known to the State of California to cause cancer, and lead, which is known to the State of California to cause birth defects or other reproductive harm. For more information go to www.P65Warnings.ca.gov.
    Weistec Horsepower 510
    Weistec Torque 490
    Manufacturer Weistec
    Street legal in all the US States No
    Engine Family M139
    Stock Horsepower 416
    See more
    year make model trim engine
    2026 Mercedes-Benz GLC43 AMG Coupe (C254) Turbocharged 2L I4 (M139)
    2025 Mercedes-Benz GLC43 AMG Coupe (C254) Turbocharged 2L I4 (M139)
    2024 Mercedes-Benz GLC43 AMG Coupe (C254) Turbocharged 2L I4 (M139)
    2023 Mercedes-Benz GLC43 AMG Coupe (C254) Turbocharged 2L I4 (M139)
    2026 Mercedes-Benz SL43 AMG Roadster (R232) Turbocharged 2L I4 (M139)
    2025 Mercedes-Benz SL43 AMG Roadster (R232) Turbocharged 2L I4 (M139)
    See more

    Product Description


    The M139 four-cylinder has always come in two factory states of tune: a base output level, and a higher "S" specification making 416 hp, which was itself the more powerful of the two figures when the M139 first claimed the world's-most-powerful-four-cylinder title. AMG has since carried that higher state of tune into its "43"-badged four-cylinder models, including the AMG GT 43 Coupe, giving what began as the compact cars' top-spec engine a home elsewhere in AMG's lineup. Mechanically it's the same architecture as the rest of the M139 family, a roller-bearing turbo, a reversed-flow head, hand-assembled under AMG's "one man, one engine" process, just running the engine's higher factory calibration right from the start.

    Weistec's calibration for this state of tune builds on that higher factory baseline the same way it does across the whole M139 family, an OEM-level ECU recalibration that works within the engine's existing turbo, timing, and knock-protection strategy rather than overriding it, with every factory safety and diagnostic system left fully intact. Starting from the M139's highest factory calibration only makes the jump more dramatic: the factory's 416 hp and 369 lb-ft climb to 510 hp and 490 lb-ft.

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    How Do You Get Your M139 43 ECU Tune Tuned?

    Follow these steps — this is what your specific vehicle needs and supports.

    1

    Unlock Check

    This ECU requires an unlock first

    Modern ECUs are often locked down, especially after a dealer software update, which can block bench flashing or OBD flashing. Our ECU Unlock Service removes those restrictions, is done per ECU, and stays active through most future dealer updates as long as the bootloader isn't overwritten.

    Read the full ECU Unlock breakdown →
    2

    Choose Your Tune Stage

    3

    Core Improvements

    Standard with this tune
    • Increased Horsepower
    • Increased Torque
    • Improved Throttle Response
    • Optimized Fuel and Spark
    • Increased Boost
    • Top Speed Limiter Removed
    4

    Free Add Ons

    Want it louder?

    Read more about Burble & Pops →

    This tune can have Burble/Pops added or increased on deceleration, at no additional charge. Select an intensity below and we'll add it to your order, or mention it when requesting your tune — through the Cypher+ app, your calibration request form, or when placing your order.

    Want to stop the stopping?

    Read more about Auto Start-Stop →

    Auto Start-Stop can be turned off as part of your ECU tune alone, at no additional charge. Just mention it when requesting your tune — through the Cypher+ app, your calibration request form, or when placing your order.

    5

    Pick Your Tuning Method

    See the full tuning process →
    1Selected

    Cypher Plus

    Order a Cypher Plus and tune your car yourself from your phone, entirely through the MyFlasher app. Watch how it works.

    2Selected — Pick return shipping at checkout

    Mail It In

    Remove your ECU or TCU and mail it to us for tuning. Required for some applications.

    3Selected — Pick Will call at checkout

    In Person

    Bring your vehicle, or just your ECU/TCU, to our Anaheim, CA headquarters. Call 714-202-0005 or email sales@weistec.com to schedule.

    4Selected — Order through your local dealer

    Cypher Pro Dealer

    Visit a certified Cypher Pro Dealer near you. Find one with our dealer locator.

    6

    Complete The Upgrade

    An ECU tune alone won't remove all factory limits or fix how power reaches the ground. Add these to round out the upgrade with no limitations.
    Read the full CPC & TCU breakdown →

    What is a CPC module?

    The CPC (Central Powertrain Control) is a separate control unit that manages things like the active exhaust valves, radiator fan, intercooler pumps, and speed limiter. On many newer Mercedes-Benz vehicles, it also houses torque limiters that can hold back an ECU tune from reaching its full potential.

    What is a TCU tune?

    A TCU (transmission control unit) tune delivers faster, firmer shifts with higher line pressure, reducing clutch slip and increasing the transmission's torque capacity. It's a worthwhile upgrade on its own, or paired with an ECU tune for a fully sorted powertrain.

    Your Total  

    Good to Know

    • This is a reflash of your original module, not a stand-alone unit.
    • Power gains vary by vehicle, modifications, fuel, and operating conditions (ambient temperature, altitude, etc.).
    • New or upgraded spark plugs are always recommended when tuning.
    • Product may not be emissions compliant. Check local laws prior to installation.
    • Always use a battery charger during programming.