I have read all the post here and got in touch with Paul to see if I could get a running capture of in cylinder pressure wave with crank sensor, I ended up with this cranking wave
I think it’s time to share something that I have introduced and tested on Autonerdz.com for the last year or so.
I think you will agree with me that the crank sensor will not lie to you as long as (in some cases} the crank pulley key way is not at fault.
I want you to think of the crank sensor as a time clock but in degrees no matter if is slows or speeds up it will always tell you the correct time in angle degrees.
The pressure wave can stretch or shrink with speed of rotation and can deceive if just measured with cursors but if we do a little math with the crank sensor we can follow it and check time.
This post started with a Pico and that’s why we should stick with it, for this discussion the PV 350 was used and did a pretty good job but a WPS 500 will do a much better.
So here we have the crank sensor rescaled and Pico zoomed
so as to view the lower peeks and place our cursor on the TDC pulse that the ECM reads as TDC Cyl1 in this vehicle.
So we take 2 measurements each 360*
Each engine will have different crank reluctor configurations but with a little math you will be able to read and measure them. In this vehicle we have 6 pulses in 360 degrees if we divide 360 by 6 we end up with 60 which means each pulse will always measure 60* no matter how wide or narrow or distance they are apart.
The Pico has a great zoom feature that will allow us to zoom in on the most important part of the wave at this point, because we want to confirm if the valve timing is out.
Now every wave is taken at different speeds so we have to do a little math and find how many degrees per ms. In our case we divide 360 by 287.7 and we end up with 1.2513 deg per ms
Let’s check exhaust valve open with the cursor set at 180*
and the other cursor set at the part of the wave that the pressure changed from a negative pressure to a positive because the valve opened to atmosphere pressure in the exhaust manifold shown by a rise. The measurement is 9.33ms now the math of 1.2513X9.33=11.6 degrees and we now know that the valve should have opened at 49* so its 37.4* late in opening.
Now how about that intake valve closing, doing the math on the second 360* we have a total time of 278.5ms so 360 divided by 278.5= 1.2926 deg per ms
Let’s move the cursors over to Bottom Dead Center remembering the 60* pulses
and put the second cursor at the point of the rising of the pressure which measured 23.73 ms
and now the math 1.2926X23.73=30.67 degrees and the spec should have been 56*After Bottom Dead Center so its 25.33* early.
You may ask why I chose the bottom of the crank signal well for convenience, if I had chose the center of that pulse
we would have a 2.9* difference, now is that too much of a error? Not when we are dealing with a cam that has an error of 25.33*
You will have a lot of success with this technique of mine, I wish you well and enjoy being able to measure valve open and closing in the coming future.