Secondary Waveform Analyzing
It seems that at least once per week, I'm being asked something about Ignition waveform analyzing. I thought I would start a discussion here with some basic information. The first thing to clarify is the name of the individual sections of the waveform, Over the years, I've seen a lot of different names for the sections, The key sections I want to talk about first is the Firing KV, which is the section at the end of the Dwell, notice the Vertical line rising, then the firing line goes down and makes a close to a 90 degree turn. The often overlooked section is the Spark KV which is where the firing KV makes the turn to begin the Burntime. The Spark KV is a VERY important piece of the puzzle because it can tell us if we have an INTERNAL or an EXTERNAL resistance problem.
When you have the waveform on the screen, Draw an Imaginary line down the middle of the Burntime, If there are any issues with higher resistance external of the combustion chamber, it will appear to the LEFT of the line, any issues to the right of the line indicates higher resistance internal of the combustion chamber.
So now you should understand why reading the SPARK KV is soo important, if the Firing KV "Jumps" out early due to higher resistance external of the combustion chamber, the SPARK KV will have increased also, but if the issue is higher resistance internal of the combustion chamber, the SPARK KV will remain basically the same.
Either condition will cause in increase of the FIRING KV and a decrease of time in the BURNTIME.
I will add some examples of Ignition waveform issues.
Here are some real world examples of Secondary waveform issues, First an internal issue of a cylinder with a partially clogged injector.
The 2nd waveform is an external issue that I caused, I removed the secondary wire from the cylinder causing a SLIGHT gap between the wire and the spark plug,
Remember that there is only a certain amount of available voltage for the secondary to operate, soo if the FIRING Voltage increases due to higher resistance , it will cause a shorter burntime then the good cylinders. But this will happen if it is an Internal or and External resistance problem, Hence the reason why looking at the SPARK KV is soo important. These 2 waveforms are from a case study the Bernie Thompson did, He removed the spark plug wire and installed an adjustable spark tester between the plug wire and the spark plug with a Small air gap, then in the second one, he increase the air gap of the test tool...… HE CAUSED AN EXTERNAL HIGHER RESISTANCE.
Secondary waveform analysis is always a fun subject. However I think you are missing one key foundation element, so I’ll ask a question and make a suggestion and we’ll see how the discussion goes.
- In the secondary circuit, when does current begin to flow?
- I suggest setting the time base to 2uS/div.
BTW I hope you’re feeling better
I like to get down into the 500ns range for nice clear definition of gaps in the firing KV. Not that I am an expert, but I can see value in putting the peddle down.
Great post and a subject that is of great interest to me. However, I do disagree a bit on the idea that the first half of burn time indicates a problem external to the cylinder. Take a look at this animation of a cylinder with a leaking exhaust valve. Notice the issue is apparent throughout the burn time event?
Turbulence in a cylinder WILL present itself before the "half way" point as the amount of spark energy required to ignite all of the cylinder does fluctuate as the cylinders compression fluctuates with the valve sealing concern.
My take is that the Kv peak is dependent on air gap, as well as cylinder compression, as the Kv demand will increase as cylinder pressure increases, as well as decreasing Kv demand with decrease of cylinder compression like seen in the animation, turbulence is just the rapid increase and decrease of cylinder pressure. I know you guys understand this, better than I do, can you George or Jim elaborate more on this for me, I'm a physics guy so that is my only understanding of the concept.
The turbulence in the animated waveform is caused by changes in RESISTENCE across the plug gap. In this case, the change in resistance is caused by rapid changes in cylinder pressure as you stated.
I wrote a class for CARQUEST Technical Institute on primary/secondary waveform analysis back in 2003. If I can find my original captures I will add them to this discussion.
YES, I also agree with you, There are times when the external issue with carry into the combustion chamber. The amount of exhaust leakage will also change the waveform, Attached is a Burnt exhaust valve, But the ROOT CAUSE of this vehicle was a clogged injector making the combustion chamber soo hot that it burnt the valve.
Jim, Here are some animations of the issues you described. 1. Lean cylinder due to a restricted injector
2. Gap in a spark plug wire
Do you feel that analyzing primary ignition wave forms have an almost equal amount value in today's vehicles, where secondary ignition is difficult to acquire do to cylinder location or coil shielding? I ask only because I find myself using primary ignition so often as I am called to look at much newer vehicles than most. I am not discounting secondary at all, if I can grab secondary, it is my "go to" signal to acquire for ignition analysis.
YES, I agree with you on this, When I can, I use the Primary in the same way I analyze the Secondary, below is an example of the SAME cylinder of a vehicle Primary (The first waveform) and Secondary (The Second waveform). VERY GOOD point Keith
Fantastic Jim anytime Im dealing with ignition always thinking what would Jim say. Your class really opened my eyes to reading what Im scoping and where I should be looking for the problem at. Thanks so much for sharing your knowledge
Me too mike. I frequently use the split the burn time line down the middle. makes secondary ignition waveform analysis much easier. The information is there, just need to figure out what it's telling you.
Hi Jim. Good work. I just covered this very same content in a apprenticeship class about a six weeks ago, started by introducing the age-old classic waveforms, breaking it into sections and exploring how external and internal conditions can affect the waveform. Getting the terminology correct is important. When introducing ignition waveforms I keep it very basic until the students have a good grasp of what they are looking at when viewing a system in good operating condition in parade, raster and super-imposed views. I then slowly introduce faults, whether it be external secondary conditions such as open plug wires, crossed plug wires or internally "doctored" spark plugs or fueling issues. I use the "piece of string" analogy to explore the relationship of firing KV and burn time and how they are affected by various conditions. Since there is only a finite time for the event to occur, the old voltmeter over time is used to explain how high and low firing KV requirements affect burn time.
While Chris and Keith have both commented that there are instances where we might question certain influences on combustion, at the introductory level of the ignition waveform, your content still forms a good foundation. Of course, with ultra high compression engines, variable valve timing, tuned induction and GDI fast becoming the norm, we do now see some variations on the classic ignition waveforms as I learned then in the '60s on the Allen scope when we still had condenser oscillations in the mix. Still, we need a starting point to work from and the classic waveforms still serve well.
So where is the youtube video of Jim teaching this class for us unfortunate souls that haven't had the priviledge of sitting in one of his classes. Maybe some day....
The longer I live the more I realize I don't know. I watched your video and am very impressed. The information was fantastic! I really hope I can learn to be as comfortable in front of an audience as you are. I was able to clear some misunderstandings and learned much more than I expected. The video seminar filled in the "why" of the "what". Thank you so much for sharing!
Thank You for the kind words, I was VERY fortunate to have a Mentor by the name of Tom McKenna, I always said that he could tell you what is in the Glove Box of a vehicle by looking at the ignition waveforms .......................LOL BTW - According to Paul from AVI, Tom was one of the very first presenters that made a training tape for Paul. I see way too many times today, specially with Ignition where the technician is going after the RESULT of a problem < But leaving the original problem still there. An example would be a lean air/fuel mixture due to a partially restricted injector, which in turn is causing a MUCH higher firing KV.
So after a nights rest I got thinking about a problem I had with my own truck. I even wrote an article about it. linkedin.com/pulse/f-150-fo… Your training would have helped me get to the conclusion quicker than I did. After seeing your presentation, I realize that I contributed to the misfire situation by raising the boost on my truck higher than the OEM designed it to run. The Bosch spark plugs may have been less prone to carbon tracking due to their design but I used dielectric grease the last go around. This according to your presentation helps with the Carbon tracking as well. I have driven about 40K since the last set of plugs installed and no misfires.
I would like to see what is going on during a hard pull like going up a hill. In your expert opinion would using a current probe be the best way to test? It looks like all the coils are powered by Fuse 99 in the Battery Junction Box. If I loop the fuse and connect current probe there, I should be able to watch all six cylinders and the driver logic. I can also backprobe a few individual cylinders on the primary signal side and see what is going on with them at the same time. From the information gained I should be able to identify other contributors and possibly prevent future problems. What are your thoughts?
Have you modified the spark plug gap to a smaller value than what the factory spec states?
Thank you Jim ! Just diagnosed a misfire using this thread as a brain refresher . Ill see if I can take some captures and explain a little later ( do not have much time being an owner and a tech ) . As always great information here from Jim .