hey everyone! say i wanted to share some waveforms ive captured and wanted some insight on the differences. keep in mind im a newer scope user and have been learning as much as i can. tool im using is a snap on zeus with just your standard alligator probes (seen the post about using different pick ups so i figured i would play around). one capture is from my personal truck, 99 f250 5.4 COP ign. followed by one of my 1968 cub cadet 125 lawnmowers with a 12hp kohler points ign system. i found on the cub that by moving my alligator lead around in different areas of the coil gave different results. for the cub i see a huge drop just before the spark line, im guessing this is the magnetic field collapsing in the coil? looking for some input here on what all is going on here because im curios now. i see that that the 5.4 (im guessing the other modulars do this too) fires the coil three times per ignition cycle until the rpms are raised off of idle.
Yes, Ford (and some Mazda) do this multistrike called thing at idle low rpm. It's supposed to help with emissions. Many will have shift to single strike at not more than1200 rpm.
The shown "voltage" level on the lawnmower is lower than on your truck. The signal strength depends in part on the coil characteristics like isolation etc.
Your lead acts as a capacitive probe and like an antenna any position change will affect the captured signal.
I don't see the downward spike being the inductive kick. This kick shows up in primary, not in secondary. Furthermore it will show as a positive voltage/upward spike.
The time base of the mower is much larger than on the truck capture. Did you use peak detect on the mower as well?
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
That I'm unsure of. Like I said I've just been playing around with this. When moving the lead around the coil on the lawnmower I was getting different strength signals. I think these were taken around the side of the coil near the top where the plug wire comes out. Now thinking about it I don't think I had peak detect I actually had to turn the filter on to get a clean wave. I was just changing oil on my sisters car (newer edge) this afternoon and wanted to see if it was similar to my truck. I was unable to get a very good signal of the secondary but I watched the trigger and I had 3 individual 5v "strikes" that was within 5 ms so I'm guessing even these newer ecoboost engines are engaging the coil 3 times. Pretty cool stuff. One thing I found out on the bigger tractors was that the scope wasn't a fan of being within a couple feet of the ignition system, I'm guessing it's RFI interference , no different then our T.V that does not like to work when we driving around the house lol. One day we'll update the wires on them......
I've been scoping some secondary patterns on small engines recently and the biggest thing I've noticed that's different then automotive is the what would be the coil dwell. small engines use a magneto type ignition system that basically acts like a alternator. I've seen on small 2stroke engines for weed trimmers the coil seems to be charged with AC or several times before it actually fires . If you connect to the spark kill tap on the coil you'll see an actual AC sine wave (not very smooth but a sine wave) that's amplitude trails engine speed. many of the more modern systems use a switching transistor to fire the oil and its all done within the coil and has a much smaller pick up coil that's tied to the gate of the switch . I have however found almost no diagnostic value in using ignition patterns for diagnosing performance issues on small engines . Other then to simply see if the coil is indeed firing I see little to no value as far as rich/lean running , valve sealing issues , bad plug ect. I would like to incorporate my scope more in my new field but I just feel like the information isn't there.
The cub runs pretty good. I have 2 125's, ones a 1968 and the other is a 1969 (had to buy the two together so the GF wasn't as disappointed I was bringing more toys home LMOA). They have a 12 Hp Kohler with your standard coil an points ignition system. I actually just got my secondary pick up kit in so I was testing that out. Sadly I could only get a few seconds off of the cubs before my scope screen started having a seizure. I'll be updating plug wires all summer at this rate. I did play around with my dad's truck. It's a 2012 F350 with the 6.2. I was able to get a pretty good signal off of the plug wires going down to the second plug (dual plug system). I found out that 6.2 strikes twice per ignition so that's pretty cool. I wasn't able to get any good signals with my test lead like how I was with my 5.4 though.
