Ignition Waveform, Turbulence?
I am new to ignition waveform analysis (Is this type of post getting old yet?), I have a case study I would like some feedback on.
The ignition capture is being taken from a COP probe, one is during the misfire at idle and the other is after spark plug replacement. Looking at the bad waveform I notice A LOT of "hash" on the spark line mostly on the right side. From what I have been reading and learning this is caused by turbulence in the cylinder? Being that this cylinder was easy to access I decided to play "Swaptronics" with the ignition coil and spark plug. I found the bad spark line followed the spark plug and when replaced the misfire was gone and my waveform looks good. I remember reading something about firing KV being used to determine in cylinder turbulence but I don't remember how so? Kv looks similar on both captures to me.
I am looking for information on why this looks like the examples of in cylinder turbulence to me as well as why a failed spark plug would cause this. Thanks for any input, I think I learn better from discussing my own experiences than others.
If you want I can come to your shop and work with you.
Thanks Justin, This car has already shipped since a spark plug fixed the misfire. I am always looking for help and knowledge though so please stop by anytime. I did keep the spark plug and have the waveforms saved.
Hey Jacob ,I am new also and really enjoy discussing this topic. I recently have been watching/learning from a video Jim Wilson made for A.V.I. Titled misfires. In this video he states the coil oscillation area gives us a picture of the left over energy. He said carbon tracking inside a coil on a high mileage vehicle will usually show up in that area under a power brake. You only swapped a plug…
Nice captures. What you are seeing is not turbulence, but the spark firing some place other than in the plug gap. When you look at a secondary voltage waveform, what the trace is showing you is the effect of the resistance in the spark plug gap. An easy way to tell if the resistance is in the plug gap is to change that resistance. This is done by snapping the throttle to WOT. You want to pull…
Albin, that is very helpful information, I will try that on the next one. Thank you for your input.
Albin your explanation was spot on.
Thanks Steve. I learned that from the Ignition guru himself, Mac Vandenbrink. Don't memorize, analyze. :)
I remember speaking with Mac on the phone awhile back. Very knowledgeable guy !! 👍
Cracked porcelain tip around electrode ???
Pay attention to the burn time as well. The good pattern has a burn time over 20 ms. The misfire one has only maybe 10 ms. Probably the porcelain inside is cracked inside the plug.
I am thankful for you guys and your knowledge. I have watched the videos and worked with scopes and I thought a bad plug would be indicated at the start of the burn. However I remember Mac Vandenbrink stating when you suspect a bad plug snap the throttle. If the pattern doesn't change the problem was outside. If it does change it is inside the cylinder affected by the compression. I love the…
Great job getting these waveforms. I like that you included the current of the coils. Usually I look at the left side of the capture as the primary side and the right side as the secondary. I wouldn't use ignition to try and find a compression or sealing issue. But maybe others would. I just think their are easier ways. Relative compression, comes to mind of course. The pattern you have, to…