Megane 3RS 273 misfire

Hi All,

I’m trying to diagnose a problem with my 2016 Renault Megane 3 RS 273. The car has no active fault codes, but I’m getting random misfires, and despite a lot of logging I still can’t find the root cause.

What I have noticed:

• Random misfires with no Check Engine Light.
• Misfires occur mainly:
  • on a cold engine with light throttle,
  • when holding a steady 1300–1400 rpm,
  • while engine speed is dropping back to idle.
• Under full throttle, the misfire counter barely increases.
• The engine runs noticeably smoother in Sport mode.

Parts already replaced:

• New spark plugs.
• New ignition coils.
• No oil consumption.
• No blue smoke from the exhaust.

Live data (Autel):
AFR during normal driving: 14.5–14.8.

• AFR under heavy load: around 12.8.

• AFR during deceleration (fuel cut): around 30.

• Short Term Fuel Trim (STFT):

• around +20% just after a cold start,
• briefly drops to around -30% after driving, then returns to around -2% after idling for a short time.

• EVAP purge command: 0%.

• Upstream oxygen sensor voltage (as reported by Autel):

• around 1950–1980 mV at idle,
• changes roughly 1950 → 2050 → 1650 mV during acceleration,
• rises to around 3200 mV during deceleration.

• Coolant temperature during logging: approximately 95°C.

• MAP at idle: around 34 kPa (about 410 mbar absolute).

The compression is good, no coolant consumption
Has anyone experienced similar symptoms on the F4Rt engine? What would you check next?

 

Yea, misfires in all cylinders. On the full load Afr is starting from 14.7 (2391 rpm) to 12.8 (4100 rpm).

Car is full stock

 

In normal mode timing advance have about 10 degree but in Sport mode it has 5 degree. You may have right.

On the full load I don’t have the misfires