Mainly regarding image four:
Is channel 'B" the exhaust or as labelled the dip stick tube?
I'm not sure what I'm missing regarding the intake valve pulsations. Haven't you labelled "Intake pulsation for No2 cyl" during No2 compression. Also, being a WPS, wouldn't the period the valve is open be a dip, therefore the dip before being the correct position?
How did you work out your degree markers, they look not quite right. But, again, I could of missed something.
A couple of other points I can see is the reduced lower manifold vacuum during the compression and power stroke of #2 although peak manifold vacuum appears to remain unchanged. I don't get that.
As I said, a nice case study. Just playing devils advocate.
Steve is out the office at the moment. I am sure he'll be able to answer your queries when he gets back (possibly tomorrow)
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I have just checked my captures and you are right, the “NOTES” are incorrect on the waveform as they indicate CHA B Dipstick when the actual annotation is correct on the image that states “Even Pulsations via Exhaust” I will ask Mike to amend this on the website.
The intake pulsation for number 2 cylinder really did give me a headache when writing this study. It does look as though the pulsation is labelled incorrectly but looking at the development of the pulse at this point from trough to peak and back to trough you can see why its formation changes during the compression stroke. The initial formation of the intake pulse during the intake stroke is normal, but its peak formation changes during the transition from Intake to the compression stroke due to positive cylinder pressure increasing whilst the piston rises. The poorly seated intake valve then allows this positive pressure to enter the intake manifold and so reveal itself to the WPS transducer during the compression stroke and power stroke, hence the reduced lower manifold vacuum.
The numbering on the waveform indicating pulsations could rightfully be moved one step to the left to align correctly with the intake strokes but they indicate the shape of the waveform at intervals between intake and compression on all cylinders to highlight the issue with number 2 cylinder. This helps to draw a comparison as we have to look for anomalies
I have attached an image that may help with the 4 stroke cycle included as a picture paints a thousand words.
The degree markers or Phase Markers were used from our Beta Software, aligning the 0 and 720 degree points on the TDC sections of the compression waveform. The Rotation Partition rulers are then used to divide equally the distance between 0 and 720 to reveal the TDC and BDC points. I have highlighted these partition markers and this may have offset their positions. The actual valve opening points do vary depending on VVT operation and so I have used markers to indicate approximate open and close points. What is important is that when overlaying 2 cylinders running under the same conditions we could reveal another anomaly. I could accurately indicate the precise point on the waveform using the phase markers and time rulers, but for the purpose of indicating the reduction in “ripple” and peak vacuum it was not necessary
I hope this helps and any feedback is more than welcome, good or bad. Take care…..SteveHi FF and thanks for the feedback. Sorry this is a late reply as I am still playing catch up. Devil’s advocate is great because we need to be challenged and test results are a typical example.
Very impressive the capabilities of the pressure tranducer, and good explanation in your case!
I do have a question/suggestion about the degree markers. Is it right that the software uses the 720 degrees markers to know the time of a full 4 stroke cyclus, and the markers used to measure a specific area are just a calculation based on that same time?
Than we have to keep in mind that the crankshaft speed is not constant, so there might be a little difference in actual timing and timing measured by the markers.
I've checked a cam/crank signal and when I compare ruler timing to the timing measured by counting tooth I see a variation of 1.5 degrees max.
I think this can be confusing, especially in case of a misfire wich causes much more variation in crank speed.
I had never thought of this before, but this process cannot take into consideration the acceleration and deceleration of the crankshaft between these intervals and so yes I would have to agree we have to tread carefully when calculating the precise valve opening times and carrying out assessments of degrees of rotation.
This is where your reference waveforms come into their own by overlaying known good waveforms taken from other cylinders or other vehicles. (Not always ideal given the potential variation in test conditions but certainly a good point of reference.)
When you couple this to the Cam and Crank correlation method as you have mentioned, having all this information on one screen gives you all data you need to make an educated and informed decision on valve timings and precise open/close points of the valve.
You have set wheels in motion in my head again and so I will try to capture a vehicle on site where by we can assess the compression waveform in relation to Cam and Crank correlation.
Thanks again for the input. Take care…….Steve
But nice write up Steve and thanks for giving my questions some thought.
Moving on a little from Arjen's input regarding crankshaft rotational speed (acceleration) after a firing event, this has intrigued me for some time as this is the method by which misfire detection is calculated. My line of thinking here is that if the PCM can see an acceleration in the rotational speed and calculate a percentage of misfire, then so should we using the scope. Here again is where I am at a loss and would value any input. I have attached a psdata file looking at CAM-CRANK-CYLINDER PRESSURE-IGNITION PRIMARY NO.1 cylinder. Moving along to next ignition event after NO.1 cylinder (identified by time rulers) I have added a maths channel to channel A measuring frequency which you might expect to see increase momentarily after the ignition event whilst on the power stroke, but the data does not support this theory!You have set wheels in motion in my head again and so I will try to capture a vehicle on site where by we can assess the compression waveform in relation to Cam and Crank correlation.
Thanks again for the input
Any input here would be most valuable.......thanks again .....take care......Steve
It's a trick I often use when looking for miss fires. Personally I would have more time on the screen and then multiply the maths calculation by X amount vertically. It's another feature I would like to see Pico adopt.Here again is where I am at a loss and would value any input. I have attached a psdata file looking at CAM-CRANK-CYLINDER PRESSURE-IGNITION PRIMARY NO.1 cylinder. Moving along to next ignition event after NO.1 cylinder (identified by time rulers) I have added a maths channel to channel A measuring frequency which you might expect to see increase momentarily after the ignition event whilst on the power stroke, but the data does not support this theory!