It has been back to Volvo for diagnostics/repair many times since (at least 7 times), staying there for over 2 weeks on many occasions. Although they have confirmed there is definitely an issue, and can log misfires on all cylinders, they have failed to find a solution. Apparently the lack of fault code makes it almost impossible for them to find the fault!?
There seems to be no hope of Volvo’s experts finding a solution any time soon and so I am hoping that users here may be able to offer knowledge, advice or share experience of similar problems.
I have an OBDII diagnostic tool and so can read/monitor parameters to help diagnose if anyone has any suggestions. I have used this so far to confirm the misfires.
As an example, a 20-30 minute journey will often have misfires logged on all cylinders, some more than others, up to around 10 misfires on each cylinder.
There seems to be two ways in which the problem presents itself, other than the logged misfires, I will provide more detail below:
Cold Start Noise/Shake
The video below shows the engine started from cold.
The engine RPM was raised to just under 2,000 RPM in this video where the problem is most noticeable.
This is very repeatable, it will occur anytime the engine is started from cold (an hour or two after being parked is usually enough), it can be noticed at idle without raising the RPM but is more subtle, raising to just under 2,000 RPM and it becomes very noticeable.
I have noticed on a cold start, the engine will fast idle for around 30 seconds, remaining at around 1,400 RPM before settling down to normal idle at just under 1,000 RPM. It is during this ~30 second fast idle period when the above problem occurs, after this period, the noise/shake will go away and raising the RPM will no longer cause the problem.
Knocking Noise Under Load
This audio clip below was recorded when driving on a slight incline at around 20MPH:
The noise will be apparent when driving at lower speeds (<30MPH) on the petrol engine, for example when the hybrid battery is depleted or set to charge, or even in AWD/Polestar Mode. The noise will be more apparent under load, often louder when going up a hill.
Again this noise is very repeatable, a low speed drive around town or around a car park it will most likely be heard, although the volume of this noise does seem to vary.
I have noticed that during the first 30ish seconds of the petrol engine starting, this noise will not be present, with the engine running smooth and quiet while driving. This is noticeable when starting to drive during the fast idle period mentioned above, or when driving along in Pure mode as the battery dies forcing the engine to start, in both cases the engine seems to run smooth and quiet for around 30 seconds before the knocking noise begins.
There seems to be a crossover point between the two problems above, where one stops and the other starts, this seems to be around 30 seconds after a cold start. I am guessing this is when the engine switches between open/closed loop mode.
If anyone has any suggestions, advice or experience with similar problems your input would be greatly appreciated.