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I need help finding a wave form online

729 Views 7 Replies 4 Participants Last post by  cobalt327
Hello there,

I am trying to find a wave form online line It is very similar to the one i have posted in the picture. There are some strange oscillations before the coil begins to increase amperage as well as after the dwell and the coil fires. These resemble flyback voltage but since this is an amperage reading it is not that....even though it may be related.

And since it is before AND after the coil charges it is throwing me for a loop. I need to find a good reference for scope patterns and possible reasons for the pattern thanks.

It is an extra credit assignment in my Fuel and Ignitions Class. We get 1 lab point for finding out what it is and that may be the difference in being top of the class or not. I haven't been able to find anything online and I have been looking for quite some time.


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OK bear in mind that it has been many,many years (maybe 35 ?)since I worked with a scope on ignition systems so my memory can be hazy but if you are talking about the oscillations at the beginning of the voltage /amperage rise and at the zero line after the coil fires I seem to remember oscillations like that being caused by burned points,with the pits and peaks causing varying degrees of resistance which would cause spiking or so called ringing oscillations.
As to finding references to scope patterns on the net,never ran across anything like this..........
Anyone else help ???
Progress:Man's ability to complicate simplicity
It's simply an inductive spike or ripple, IMO. More HERE.

Is the trace you are working w/from your class, of a points-type ignition system? If so, the points' resistance as well as gas ionization could be a factor, as well.

Like shelby it's been almost 50 years since I took the ignition class... You get the ocilliations after the spark fires when the magnetic field collapses to fire the plug. this collapse of the high voltage side of the coil induces a magnetic field in the low voltage side of the coil. which then induces another field in high voltage then the low voltage side until it finally cancells out. with a points ignition the condensor is matched to this induced voltage to minimize point spark and burning .. I don't remember the pre spark wiggle in the curve but it could be caused by the current " loading" up the primary coil which would induce the secondary coil and that magnetic field adding a field back to the primary coil windings.. Just a guess on that.
Thanks for the replys, keep In mind that this is amperage we are talking about, the oscillations after the coil fires are related to the flyback voltage that is produced but the trouble I am having is with the oscillations before the coil primary circuit begins to build amperage. Thanks for the leads on the points type ignition, any ideas on how something like this could occur in a DIS ignition?
Intuitively, I would tend to think it involved the switching circuit(s), be it transistor, or whatever. It also seems as though the sheilding is insufficient to prevent induced eddy currents- which could be what's showing up on the trace.
Cobalt was the closest, the ripple in front is normal apparently, and the oscillations afterwards are where the problem was. This was a Coil on Plug system and the problem was a bad sparkplug, apparently the amperage had to try hard to overcome the resistance and when it finally did not find a path to ground it sent all the amperage oscillating back into the coil.

They told us what it was a day early otherwise I probably would have found it. I ended up getting the top score in the class regardless, thanks to all who helped

Double_v23 said:
This was a Coil on Plug system and the problem was a bad sparkplug
Congrats on your score!

That was almost a trick question, because they didn't provide you w/the readout of what all of the plugs were doing. The bad plug would've stood out from the others, deductions would have been made easier. But the instructor wanted you all to think- which is a good thing, in the end.
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