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ignition wavepattern in depth info

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22 Aug 2020 10:46 - 22 Aug 2020 10:48 #42410 by Matronix
ignition wavepattern in depth info was created by Matronix
There are quite a few basic scope ignition lessons on the site and video's about 'in the field' stuff even more... still most of them come back to the basic stuff. A lot of them have about the same principle errors like shorted coils (ramp measuring), rich misfires (sloping down firing line), lean misfires (sloping up firing line and possibly high end energy), weak coils (rasing rpm with some load), etc. All are quite easy to read and interpret.

In reality what we run into (or I at least, my guess is more people will) is a host of other issues which give way less clear indications. I recently learned a lot about reading the height of firing kv, dividing first part firing line and second part (outside / inside cilinder issues), etc etc but still run into so many new things where you won't read about on the net (not easy that is, since it most is about basic info and common issues).

If you have / wan't / care to do stuff about this, it would be a great benefit for people that will help to understand things going wrong inside an engine and preventing moments of unnecesarily tearing apart a head if for instance, only a hydraulic valve / lifter is the issue. There are lot's of waveforms that may tell a lot, but are not 'as easy to read' regarding the cause of the image at hand

Example: what if we have a good starpoint (burn line) but halveway the line we get a saw tooth figure or extreme hash, or the other way around, extreme hash in the first part of the line (fouled plug for instance) , what if starting point is higher (trouble starting the burn due to compression, or mixture, etc.) . Think there is a lot to be learned on this for lot of people and it relates to diagnosing stuff which take a lot of time to diagnose by just taking an engine apart (if that will tell you what is going on .. which is not always so)

Another example - when doing relative compression, we see differences... still, if you do a leak down test, cilinders test 'no leak'... what next now your basic trouble shooting tool has failed :)
Last edit: 22 Aug 2020 10:48 by Matronix.
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22 Aug 2020 12:03 - 22 Aug 2020 12:19 #42412 by Noah
Replied by Noah on topic ignition wavepattern in depth info
I agree that there are many different scenarios and variables that can effect the secondary ignition waveform.
I like learning about the secondary ignition theory, and would like to see more myself. Admittedly, it is not a part of my diagnostic routine.

The important thing to remember is that we are not going to use the evidence gathered from a secondary pattern alone to move forward with major engine disassembly.
If you see a pattern that indicates a potential mechanical issue, you must then prove it with another test.
Lets use your low compression, no leak scenario. That's not so much of a basic troubleshooting failure as it is a failure to understand what the results of the test are telling the technician.
With some knowledge of the workings of a 4 cycle internal combustion engine, we can deduce that if low compression is not the result of a leak, then it must be from a different kind of failure. Clearly not a sealing issue, hence no leak, so it must be a valve opening issue.
if the exhaust valves failed to open, we would not have low compression, so it can be determined from the compression test and leak down test that the intake valves are not opening.
We may be able to see that and back it up with an in cylinder test or manifold vacuum waveform.
Now we have the evidence needed to begin disassembly of the engine to determine why.

The largest hurdle for me when learning the techniques taught by Scanner Danner and others online is that there is a finite number of faults that can cause the symptoms observed. I tend to see new information as bits and pieces. I can see how those pieces fit together, but I'm not sure if those pieces are the whole picture until I start experimenting, testing and defining the process in my own terms.

Too much plus more equals just right.
Last edit: 22 Aug 2020 12:19 by Noah.

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23 Aug 2020 14:06 #42442 by Weycraze
Replied by Weycraze on topic ignition wavepattern in depth info
I have found this to be one of the best Secondary Ignition resources out there. It's Mac's old Bible. A gem it truly is.

cody.inlandgps.com/pub/Scope%20Book%2035115.pdf

Enjoy
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