Simply display the compression waveform on your PC desktop from the scope software you are using. Obviously, if your scope does not have the ability to save waveforms to a PC, this is not going to work for you.
Once the waveform is displayed on the PC screen, hold down the ALT key while you also hit the PRNT SCRN (print screen) key. Actuating these two keys will make a copy of anything that is on your PC screen at the time and save it to a hidden place called a "Windows Clipboard."
Once you have done this, bring Microsoft Paint up on your PC screen. Go to the tool bar at the top left of the Paint program. Click on "Edit" and then select "Paste" from the drop down menu. Once you select paste, the scope image, or any other image from your PC screen, will transfer from the Windows Clipboard area into the Paint program.
Now that you have the scope image showing in Paint, choose the "Line" tool from the Paint tool bar on the left of the screen, shown here inside a red box. Then move the PC's cursor onto the scope image. You will notice that your cursor now looks like cross hairs on a gun. As you are moving your cursor across your waveform graphic, notice there are two sets of three-digit numbers displayed at the lower right hand side of the Paint program screen. There is a comma separating these two sets of numbers. The first three numbers track the horizontal positioning of the cursor; the second three numbers track the vertical positioning of the cursor. The first three numbers that track the horizontal positioning are what we will use to mark off our 720 crankshaft degrees shown on this compression waveform.
Next, place the center of that cross hair/cursor at the very peak of the first compression waveform on the left of the screen. Record the first three-digit number displayed on the lower right of the Paint program screen. This position in our example is 341. This is the horizontal position of the first peak. Then click and drag a line from the peak of the compression waveform to the bottom of the screen.
However, if your background is the same color as your line, you will not see the line. Choose a different line color from the color palette on the lower left of the program screen. Next, place the cross hairs/cursor over the second compression peak and record this horizontal position displayed on the lower right. It was 989 in our example. Drop a line from the second peak.
You now have two vertical lines along with two three-digit numbers that correspond to the horizontal positions of those lines. In our example, pixel 341 is for the first peak and pixel 989 is for the second peak.
Subtracting 341 from 989 gives you 648, or the amount of pixel-spread between those two peaks. In other words, it takes 648 pixels to travel 720 crankshaft degrees in this scope picture.
Take the spread number of 648 and multiply it by 0.25, which gives you 162. This gives you the amount of pixels you must travel to the right of our starting point of pixel 341 in order to move one quarter of the distance from the first peak toward the last, or 180 degrees of crankshaft rotation (162 + 341 = 503). At pixel position 503 drop another line. This is our 180-degree mark marking the beginning of our exhaust piston stroke.
Next, multiply the spread number of 648 by 0.50, which equals 324 (324 + 341 = 665) Pixel 665 is the 360-degree mark.
Spread number 648 times 0.75 equals 486. 486 + 341 = 827 or 540 crankshaft degrees. You now have all 4 strokes marked.
EXTRA CREDIT: What would you multiply the spread number by to mark off each 90 degrees of rotation? How about each 30 degrees?
Use this method to not only mark up your compression waveforms but any waveform at all using any signature in a waveform that you choose.
Jim Garrido of "Have Scanner Will Travel" is an on-site mobile diagnostics expert for hire. Jim services independent repair shops in central North Carolina. He also teaches diagnostic classes regionally for CARQUEST Technical Institute.
