[user0086]

Hi.

After replacing the high-pressure fuel pump on a R56 with the N18 engine (early MEVD17.2.2 ECU), the engine runs rich at idle. Previously it ran lean because the old HPFP couldn't reach target pressure.
With the new, OEM, HPFP the target fuel pressure is reached normally. It fluctuates a bit, but that is also the case on a known good N18 that I have in my shop as well.

Symptoms:

• Multiplicative fuel correction keeps increasing at idle
  
• Long-term and short-term fuel trims are very high (positive) in EOBD data
  
• Wideband / AFR sensor correctly reads rich (almost 5v in i5тд), yet the ECU keeps adding fuel
  
• Post-cat O2 sensor appears inactive — I assume this is a consequence, not a cause
  
• The multiplicative fuel trim in i5тд goes to about 1.18
  
• The EOBD values reach +25% long term and about +15% short term.
  
• After resetting the adaptations it's temporarily back to 1.0 (i5тд) and 0% (EOBD)
  
• All cylinders are equally rich and fuel pressure does not drop quickly after engine is switched off (e.g. injectors don't leak)
  

What I've tried:

• Reset engine and VANOS adaptations with i5тд
  
• Updated ECU to latest software via WinKFP / ñc5 ёxpёят
  
• Re-learned Valvetronic limit positions
  
• Disconnected one or both O2 sensors — still runs rich, trims still climb
  
• Disconnected camshaft sensor to disable VANOS — no change
  
• Repeated the above steps multiple times
  

It seems like the ECU is commanding more fuel regardless of what the sensors report. The issue seemingly started with the HPFP swap, or it could have been here before.
Any ideas what could cause the ECU to ignore the rich condition and keep increasing fuel trims?