PicoScope 7 Automotive
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Cranking vs Running compression
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Andysgarage
- Newbie
- Posts: 1
- Joined: Fri Jun 19, 2020 1:28 am
Cranking vs Running compression
Hellow everyone. I just purchased a WPS500x and something need some clarification is, when you need to do a in cylinder compression using the wps, which is more important, cranking or running? If Both, what is the importance of one vs the other?
Thank you in advance
Thank you in advance
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Steve Smith
- Pico Staff Member
- Posts: 1589
- Joined: Sun Aug 25, 2013 7:22 am
Re: Cranking vs Running compression
Hello and thank you for the post
There is a lot to consider here but this depends upon what you are looking for.
For a compression test alone, then Cranking at WOT is fine (revealing Peak pressure and compression tower formation)
However (and far more conclusive) for detailed analysis of the cylinder performance and all the events taking place throughout the 4-Stroke cycle then engine running at idle speed is preferred.
With the engine running at idle you can determine:
Cylinder leakage, Valve open/close events, valve duration, VVT control and phase shift, exhaust back pressure & individual cylinder valve timing/comparison to name just a few key points of interest
The following forum posts and Technical notes will help here:
https://picoauto.com/library/training/p ... transducer
https://www.picoauto.com/library/traini ... -diagnosis
post89721.html#p89721
topic17241.html
viewtopic.php?p=100606&sid=3c8a6f73a0ae ... 33#p100606
We have a number of WPS case Studies too
https://www.picoauto.com/library/case-s ... ault-codes
https://www.picoauto.com/library/case-s ... -non-start
https://www.picoauto.com/library/case-s ... 0695e7c939
I hope these help, take care......Steve
There is a lot to consider here but this depends upon what you are looking for.
For a compression test alone, then Cranking at WOT is fine (revealing Peak pressure and compression tower formation)
However (and far more conclusive) for detailed analysis of the cylinder performance and all the events taking place throughout the 4-Stroke cycle then engine running at idle speed is preferred.
With the engine running at idle you can determine:
Cylinder leakage, Valve open/close events, valve duration, VVT control and phase shift, exhaust back pressure & individual cylinder valve timing/comparison to name just a few key points of interest
The following forum posts and Technical notes will help here:
https://picoauto.com/library/training/p ... transducer
https://www.picoauto.com/library/traini ... -diagnosis
post89721.html#p89721
topic17241.html
viewtopic.php?p=100606&sid=3c8a6f73a0ae ... 33#p100606
We have a number of WPS case Studies too
https://www.picoauto.com/library/case-s ... ault-codes
https://www.picoauto.com/library/case-s ... -non-start
https://www.picoauto.com/library/case-s ... 0695e7c939
I hope these help, take care......Steve
Re: Cranking vs Running compression
In the old days prior to transducers, the difference between cranking and running compressions was chalk and cheese. One would pick out a broken valve spring and the other couldn'twhich is more important, cranking or running? If Both, what is the importance of one vs the other?
With transducers such as the WPS you could probably see more detail in a cranking test.
I would be inclined to keep both tests available to me and use them both.
Re: Cranking vs Running compression
For valve timing I rather use cranking compression with blocked throttle to create vacuum in intake.Why?Because with running compression there isn't constant engine cylinder speed because one cylinder is misfiring (the one where is WPS sensor) and that cylinder is slower than others causing that timing rulers in Picoscope software doesn't represents precisely valve events.It's close but it's not precise.
On other hand during cranking compression all cylinders are rotating with similar speed and timing rulers represents more accurately valve events.Blocking intake throttle is needed for creating vacuum so that valve events are obvious.That's way I'm a lot more confident in this way of measurement for static engine timing.
Of course for dynamic timing check engine must be running and for other mechanical checks other methods are used..
That's my experience in that field and my opinion.
Best regards,Dejan
On other hand during cranking compression all cylinders are rotating with similar speed and timing rulers represents more accurately valve events.Blocking intake throttle is needed for creating vacuum so that valve events are obvious.That's way I'm a lot more confident in this way of measurement for static engine timing.
Of course for dynamic timing check engine must be running and for other mechanical checks other methods are used..
That's my experience in that field and my opinion.
Best regards,Dejan