Problem with W204 RPM Fluctuations

[blueabyss]

I found one test and photo on my PC when I was solving a similar problem on W211.
In DAS this test looks like this: if you look at the log, the desired current value (A) and the actual current value (A) are higher - why? The device tries to close the DRV but cannot because the rail is damaged by the assembly. That the current value is higher than it should be. Why? The unit cannot close the DRV because the rail is damaged.

I still remember how the tightness of the rail was checked.

0. Dismantle the overflow rail.
1. Disconnect the metering valve on the pump!
2. Disconnect the injectors!
3. Connect +12V to the DRV - this will completely close it.
When starting the engine, diesel should not flow out of the overflow rail.

 

[B0bby92]

Many thanks to blueabyss for this information and help. Unfortunately, I am not that professional. I will try to replace the common rail with a regulator (never removed) from another car and report the results.

 

[B0bby92]

Another thought, could a faulty O2 sensor be causing these fluctuations?

 

[blueabyss]

Try one of the possible options.
I do not think that the O2 sensor can cause these anomalies, but I'm not sure without measurements.
If you cannot exclude the malfunction for a test rail replacement, I would look at the bridge clutch of the torque converter. This is where the torque converter bypass clutch should be temporarily disabled in the Xentry.
If you disengage the clutch, the symptoms it may have caused will disappear - be careful, the car will start to slide.

 

[nano5849]

Another thought, could a faulty O2 sensor be causing these fluctuations?

Yes, because the O2 sensor determines how much fuel should be injected. If it is faulty, its readings will be erratic, which will cause problems with the fuel injectors not injecting enough fuel or injecting too much fuel in an attempt to maintain the A:F ratio at 14.7:1.

 

[B0bby92]

Yes, the O2 sensor has been completely dead lately (Check Engine light came on and Xentry diagnostics showed it). I will replace it and report back to share.

 

[blueabyss]

Yes, because the O2 sensor determines how much fuel should be injected. If it is faulty, its readings will be erratic, which will cause problems with the fuel injectors not injecting enough fuel or injecting too much fuel in an attempt to maintain the A:F ratio at 14.7:1.

Attention mate, we are talking about a diesel car. This engine runs on excess air.

 

[B0bby92]

The torque converter has been recycled.

 

[nano5849]

Attention mate, we are talking about a diesel car. This engine runs on excess air.

Thanks for the correction, I was speaking in general terms.

 

[blueabyss]

The torque converter has been recycled.

I would like to note that the fault may also be in the torque converter clutch bypass valve - it stalls. Diagnostics does not reveal this defect. Again, this can be found out from the actual values - consumed and actual current (A) for a given valve. Again, the test can be performed by disabling (Xentry) the inverter bypass clutch. Applies to gearbox (722.6).