Primary voltage on a waste spark distributorless ignition

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Primary voltage on a waste spark distributorless ignition

Postby AdvTechTS » Wed Jun 18, 2014 1:24 pm

Hi All,

My name is Chad and I have just taken delivery of a sexy new Pico Advanced 4423.
I did my apprenticeship in the mid 80's and used a number of Vane, Allen and Sun engine analysers through until the late 90's. Since that time I have rarely used a scope but after a few difficult to diagnose vehicles I have re-aquainted myself.

My first real test was an intermittent misfire on a Suzuki Swift M16 engine with a waste spark distributorless ignition system. While testing the system I was able to diagnose the faulty coil, however the primary voltage did not look anything like I thought it should (I have tested a lot of waste spark systems in good old days, but these were all controlled by an ignition module rather than the PCM).

I have searched the forums, tutorials etc and cannot make sense of the primary voltage and I'm hoping someone can explain it to me?

suzuki_swift_rs416_scope_ignition_primary_current_2-3.png
Primary current


suzuki_swift_rs416_scope_ignition_primary_2-3.png
Primary voltage at the good coil (2-3)


suzuki_swift_rs416_scope_ignition_primary_1-4_misfire1.png
Primary voltage at the faulty coil (1-4)


suzuki_swift_rs416_scope_ignition_secondary_kV_2.png
Secondary kV at the good coil (2)


suzuki_swift_rs416_scope_ignition_secondary_kV_4_misfire.png
Secondary kV at the faulty coil (4)


based on the secondary kV I swapped the coil locations and the fault moved with the coil, so a new coil was fitted and all is good.

Thank you for taking the time to read my post and I hope you can shed some light on this for me.
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Re: Primary voltage on a waste spark distributorless ignitio

Postby Steve Smith » Thu Jun 19, 2014 12:18 pm

Hi Chad and thanks for the post regarding CDI (Capacitive Discharge Ignition), hence your concern about the primary ignition voltage waveform.

This type of ignition system relies upon the discharge of a capacitor into the coil primary (400v+) to generate the typical voltages we expect at the secondary.

Unlike the inductive type ignition system where you can plot each event during the dwell, firing and burn periods, with capacitive discharge ignition you will only see the release of the capacitor high voltage into the primary followed by the dissipation of voltage (coil ringing).

It is great to see these images of before and after, as we can see the effects on the secondary coil due to the inefficient capacitor discharge into the primary.

Looking at the primary current, was this taken from the good coil and if so do you have the current waveform from the faulty coil as the capacitor failure should also affect the current flow?

Take care……Steve
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Re: Primary voltage on a waste spark distributorless ignitio

Postby Autonerdz » Thu Jun 19, 2014 2:54 pm

Steve,

Look again at the primary current waveform. This is inductive discharge not CDI.
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Re: Primary voltage on a waste spark distributorless ignitio

Postby AdvTechTS » Thu Jun 19, 2014 3:04 pm

Thank you Steve,
I have the Ignition System section from the factory manual and it only refers to it as distributorless.

99500-63J10-01E 407.pdf
Suzuki Ignition System - Description
(74.96 KiB) Downloaded 222 times


I saw reference to Saab CDI in your (Pico) documentation but as I wasn't testing a Saab I ignored it! Suzuki however use it in a waste spark configuration rather than full COP.
Now that I have read it I can see the difference in the wiring diagram (permanent earth at coils) of the Suzuki.

99500-63J10-01E 408.pdf
Suzuki Ignition System - Wiring
(94.08 KiB) Downloaded 197 times


99500-63J10-01E 242.pdf
Suzuki Ignition System - Sample waveforms 1
(119.75 KiB) Downloaded 240 times


99500-63J10-01E 243.pdf
Suzuki Ignition System - Sample waveforms 2
(112.65 KiB) Downloaded 164 times


I still have the car here and the faulty coil so I will refit the faulty coil and grab the primary current waveform and upload it tomorrow.

Can you shed any more light on the CDI primary voltage waveform?
What is the small event that can be seen prior to the discharge?

If if helps I also captured a primary current vs voltage.

suzuki_swift_rs416_scope_ignition_primary_current-vs-voltage_1-4-2-3.png
Primary current vs. voltage


I would also be interested to know what other modern cars are using CDI Ignition for future reference if anyone else can contribute...

Thank you greatly, Chad.
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Re: Primary voltage on a waste spark distributorless ignitio

Postby AdvTechTS » Thu Jun 19, 2014 3:17 pm

Autonerdz wrote:Steve,

Look again at the primary current waveform. This is inductive discharge not CDI.


Can you elaborate on this?
I have not used primary current waveforms in the past, how do CDI differ from inductive?
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Re: Primary voltage on a waste spark distributorless ignitio

Postby Autonerdz » Thu Jun 19, 2014 3:54 pm

Chad,

I see the problem now. Thanks for putting up the diagrams. We don't have that model on this side of the pond.

You will not be accessing primary on that design. That is power transistor ignition. The power transistor and coil primary are coil internal. It's still a typical inductive discharge design and not CDI.
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Re: Primary voltage on a waste spark distributorless ignitio

Postby Steve Smith » Fri Jun 20, 2014 9:46 am

Wow thanks for the replies and feedback on this one. It is not very often a technician is willing to reinstall a faulty component to grab additional waveforms, and for this we are most grateful, thank you.

Thank you to Autonerdz too as you cannot argue with the wiring diagram, not a capacitor in sight, sorry.

I compared the peak current with a Saab waveform I have here and they are not too far apart. I have included the SAAB waveform below which is the only major automotive manufacturer to have utilised CDI in such volume. Now Saab are no longer, I don't know who is using CDI to great effect?

Regarding

What is the small event that can be seen prior to the discharge?


This is called the "Polarity Peak", and seen as the magnetic flux builds at the start of the saturation/dwell period.

Does this event align with the commencement of the "IGT" signal (Igniter trigger "On" point.) The commencement of current flow into the primary?

SAAB 95 2.0 B-ENG.psdata
(806.64 KiB) Downloaded 153 times
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Re: Primary voltage on a waste spark distributorless ignitio

Postby AdvTechTS » Sun Jul 06, 2014 12:02 pm

Hello all, sorry for the delayed response. After refitting the faulty coil and getting the faulty ignition primary current waveform I left the file unsaved while I reassembled the car. My daughter (on school holidays) came along a played with the computer and deleted my image... I didn't realise this until after the car had been collected :(

So, I have photoshop'd the a good waveform to represent the faulty waveform (to the best of my recollection).
The main features were the noise at the current peak and absence of the small downward spike at the ignition point.

suzuki_swift_rs416_scope_ignition_primary_current_1-4_mockup.png
Mockup of Primary Current at the faulty 1-4 Coil


Steve - I hope this helps!

Question:
Looking at the 'Secondary kV at the good coil (2)' in my first post, what is it that causes the oscillations to straddle 0 Volts and is the 'Burn Time' consumed within the oscillations?

All of your thoughts are much appreciated!
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Re: Primary voltage on a waste spark distributorless ignitio

Postby Steve Smith » Tue Jul 08, 2014 12:41 pm

Hello again and thanks for your perseverance given the school holiday incident which made me smile. (I understand the scenario believe me)

I have attached a very similar waveform from a GT86 which demonstrates the rapid inducement of voltage into the secondary circuit as the primary is switched off.

I have searched high and low for a waveform with these characteristics including both the IGT signal and current as these would help to explain the process far better.

Tomorrow I hope to locate a GT and carry out the above test with all the data on screen, where I will post it here.

Burn time can vary from 1.0 ms to 2.5 ms and in the example attached we have an approx burn time of 2.4 ms including the oscillations. Looking at your "secondary kV at the good coil (2)" we have approximately 1.5 ms.

GT86 IGNITER.psdata
(236.26 KiB) Downloaded 122 times


Once again thanks for the feedback and I will post the full waveform here ASAP.

Take care......Steve
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Re: Primary voltage on a waste spark distributorless ignitio

Postby AdvTechTS » Tue Jul 08, 2014 12:50 pm

That would be wonderful Steve, Thank you:)

:idea: NOTE TO ALL NEW PICO USERS :idea:
Remember to turn off your inductive amp clamps when you are finished each job, otherwise they'll be flat when you go to use them next time :?
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