Waste spark wave form question

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Waste spark wave form question

Postby roadserpent » Mon Jan 19, 2015 5:03 am

After finding the reason for long cranking times on a 2002 dodge neon with a 2.0L inline 4cyl, I had time to play. The ignition system was my first choice. It is a waste spark system using one molded plastic housing containing two separate coils. After capturing some wave forms I shut the engine off and took some time to look at the wave forms and relax. I notice that the coil that fires #1 and #4 cylinders has no oscillations after the spark line. It is shown in both secondary captures and in the primary voltage wave form. Is this coil possible borderline? Or is this normal? The engine runs fine.I will attempt to attach 3 files for you.
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Dodge_Neon_2002_Petrol_Secondary_20150118-0002.psdata
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Re: Waste spark wave form question

Postby Henri Malcorps » Sat Jan 31, 2015 9:02 pm

Hello Roadserpent,

I couldn't open your attachment but the oscillations at the end of the spark line, to check if there is sufficient energy in the coil, is no longer a valid test. I have a MGTF of 2005 which has also a wasted spark ignition system and there is only one oscillation after the spark line. In fact this has nothing to do with the wasted spark, more information may be found at http://www.diagnosticnews.com/diagnosti ... agnostics/
I have a question for you. I guess you use a M1074 secondary ignition pickup, what is the firing kV that you find?
I don't use a Picoscoop but a DSO that I also use for other applications. To find the firing kV the voltage measured with the secondary pickup should be multiplied by 10000 (documentation sheet of the M1074). If I do this I find 20 kV what seems very high, about half of this voltage is expected. I don't know how the pickup works, I guess it is a capacitive devider where one capacity is the HT cable and the second should be in the black box that is connected to the earth. But this means that the result depends on the properties of the HT cable. Do you have some idea's about this?

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Re: Waste spark wave form question

Postby roadserpent » Sun Feb 01, 2015 7:32 pm

136 views of my post and no replies, Incredible ! Henri I used a 4423 4 channel picoscope with 2 pico PP178 secondary pickup leads. each of the leads look to have some kind of attenuator device built into it as the scope is only capable of a maximum of 100 volts input. Two coils molded into one plastic housing, one fires cylinders #1 and #4 and the other fires cylinders #2 and #3. The coil for 2 and 3 has oscillations after the spark line (shown in primary and secondary wave forms) and no oscillations after the spark line on the coil for cylinders #1 and #4 (shown on primary and secondary wave forms). I thought this to be odd, so I posted it. The KV of the firing line runs between 3.6 and 7.5 KV for non event cylinders and between 10.6 and 21 KV for event cylinders on the coil that lacks oscillations. The coil with oscillations has firing line voltages between 4.6 and 5.2 KV for non events and between 11 and 21 KV on events. The engine runs fine now but wondered if this was the start of a problem. I will test more cars using this coil pack as they come in the shop. What a huge amount of info that is in these waves, I haven't time to tell you about spark line voltage or duration.
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Re: Waste spark wave form question

Postby Robski » Sun Feb 01, 2015 8:46 pm

136 views of my post and no replies, Incredible !

maybe a few are like me & CBA downloading files, try posting pics & annotate them see if anything changes (leave properties tab open).
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Re: Waste spark wave form question

Postby Henri Malcorps » Mon Feb 02, 2015 10:19 am

Thank You Roadsepent,

Variations between 10 and 20 kV seems very high to me. I don't know the PICO scoop, but are you sure you are not undersampling your signal. If the firing line is about 1µs wide and your sample period is also 1 µs, you can sample anywhere on the firing line and you can have a very wide range of kV. I also experienced this and now I always use at least 25 samples per µs or 25MS/s. The maximum kV is than much more stable.
I downloaded the Picoscoop software and could now open your file, but time resolution didn't allow me te have a clear view on the oscillations. Anyhow, I think that if your sparkline is long enough, I wouldn't care.

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Re: Waste spark wave form question

Postby AuthorMike » Mon Feb 02, 2015 10:36 am

Robski wrote:
136 views of my post and no replies, Incredible !

maybe a few are like me & CBA downloading files, try posting pics & annotate them see if anything changes (leave properties tab open).


We actually encourage the uploading of PSDATA files to allow both Admin and other users to interrogate them directly.

Perhaps uploading a file and annotating an image is a good idea, but the PSDATA as a minimum is the best bet for the reasons outlined above.

If there are those on the forum who do not wish to spend the time downloading PSDATA files to assist others that is their choice...


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Re: Waste spark wave form question

Postby Henri Malcorps » Mon Feb 02, 2015 11:11 am

Roadserpent,

Are you sure you have a good earth connection for the pickup? Your sparkline seems to be too low to me, normaly it should be about 2 kV. Also for the cylinder without oscillation: the voltage after the sparkline returns to the same level as during the spark and is decreasing very slowly.

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Re: Waste spark wave form question

Postby Robski » Mon Feb 02, 2015 6:24 pm

We actually encourage the uploading of PSDATA files to allow both Admin and other users to interrogate them directly.

Yes I know, I never encouraged him not to. I thought I was giving the guy a possibility..... obviously not.
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Re: Waste spark wave form question

Postby sigoaprendiendo » Mon Feb 09, 2015 12:15 pm

Hi everybody

When I compare both nose for cylinder three and four this is what I think: :wink:

Oscillations in the number three shows a larger amount of energy that hasn't been consumed thoroughly by the firing event, so this suggests me that there is a slight lack of fuel in this cylinder.

I would compare injectors activation time for number 3 and 4 to see what is going on.

If there is any difference between this times then try to make a snap test for the same capture above to avoid computer from adjusting injection time. This way the secondary ignition pattern will show how much energy is really available for both spark plugs

I hope this help :idea:

Kind regards
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