Hello and thank you for the reminder on this post (It feels like "generations" ago)
The image I believe we are referring to is below
The sudden drop in pressure is caused by the rotation of the engine as the applied pressure (Cylinder leakage test) increases. Once the engine is locked the pressure can increase
Looking at your scenario below
This is very interesting indeed and my first question is what is the customer complaint?
Secondly do we have a measurement error?
For example do we have any leakages or interference from outside sources?
Can you reproduce this symptom on all cylinders?
Looking at the sudden fall in pressure on the rising face of the compression tower, if this is a "real" scenario we either have a sudden leak or a sudden change in cylinder volume (Both will cause a pressure drop)
Looking at the expansion pocket, once again, if this is for "real" and not a measurement error then we have a sudden leak
How does the in cylinder capture look during cranking? (Perhaps restrict the intake to emphasize the intake and expansion pockets) This will help determine if combustion is contributing to the formation
Perhaps inhibit any VVT operation too
How is cranking speed, is it uniform or does it momentarily reduce in speed?
Any feedback would be most welcome
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