Ignition

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Ignition

Postby mteste03 » Mon Oct 29, 2012 9:25 pm

Hi all,

Trying to get to grips with the pico scope and would like to ask for comments on the attached waveform.

Would I be correct in thinking that the primary earth is incorrect, from all the information and example waveforms I have looked at I would expect approx 500mv rather than 2 volts??

Also the current switch off seems a bit odd while also taking a long time? Lastly I dont understand why the current can go negitive. Is it linked to back EMF???

Thank you in advance for the help

Matt
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Re: Ignition

Postby Robski » Tue Oct 30, 2012 3:53 pm

Firstly what vehicle is this from ?

At first glance it appears to be current limiting & yes switch off looks very slow.
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Re: Ignition

Postby mteste03 » Tue Oct 30, 2012 4:26 pm

Hi,

volvo 240 2.0 non turbo 1994
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Re: Ignition

Postby Robski » Tue Oct 30, 2012 6:38 pm

How's about a brief insight to the issue with the car etc.............. you get out what you put in :!:
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Re: Ignition

Postby mteste03 » Tue Oct 30, 2012 7:12 pm

Sorry didn't give you any background info.

There isn't an issue with the car as such. Did some other small jobs on it and had some spare time at lunch so thought I would try getting a bit of pratice with the new pico. Trying to get to grips with setups etc.

Been looking through Frank Massey books, CDs and tech topics sutff to learn a bit more and trying to get examples of good cars etc for future ref. Trying to understand what I am seeing on good cars with the hope of learning how to spot things with problem cars.

From what I feel that I have learnt and seen so far I was just wondering if there was a problem arising with this ignition system. Was expecting to see the voltage get much closer to 0v than it did. Was thinking that by not reaching near 0 the coil isn't being fully fluxed thus reducing spark energy. So maybe the car could be running better of maybe just prevent a problem occuring soon. Though I could be completly wrong here, so was just hoping to get someones elses input who has much more experience. Guess no matter how many books you read of courses you attend theres always another question.

Really hope you dont think I am wasting your time or asking silly questions. Just lacking experience with day to day use of this new gear.

PS Robski I have found your replys on here and other sites very intresting and great learning so thank you for taking time to share your knowledge!
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Re: Ignition

Postby Robski » Wed Oct 31, 2012 7:43 am

Buy yourself an adjustable spark tester & test the coil output, this should put you in a direction if anything is amiss.

If I had the right diagram up last night then there is an amplifier & ign control module in the loop.

PS you either have unwanted resistance or it is current limiting,but why on the current ramp is it not a straight limit ??

Also iirc you didn't zero the amps clamp.
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Re: Ignition

Postby mteste03 » Wed Oct 31, 2012 1:25 pm

Hi,

Now I come to think of it you're correct; I disconnected the current clamp and forgot to zero it again when I reconnected to scope to take this capture. That explanis that. WONT forget that again lol.

Yes the vovlo information agrees that it has both componets. The amp is bolted to the inner wing and module inside the car. My expectation would be that current limiting would remain stable but I am fairly new to this so have little experience. Can't find any conclusive info about the operation of the device (if current limited or not).

If the amp was breaking down under load could that explain the drop in current. As the temp increases the resistance of the solid state componets increases thus reducing current flow.

Will get a spark tester and try and get the car for a few hours to see what the result is. Will also load test the wiring while at it.

Will update you as and when

Thanks for the suggestions and advise
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Re: Ignition

Postby Autonerdz » Wed Oct 31, 2012 3:03 pm

Also the current switch off seems a bit odd while also taking a long time?


Matt,

Your current cut off time is fine at about 15µs. Current level is also good so you have a valid primary drive....everything the coil needs to work.

Lastly I dont understand why the current can go negitive.


It doesn't. That's EMI. Even though the probe is well shielded, you will get this in proximity to the coil. If you move your test point away from it....maybe to a common power supply to the coils, you won't get that.
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Re: Ignition

Postby Robski » Wed Oct 31, 2012 3:58 pm

Matt,

Your current cut off time is fine at about 15µs. Current level is also good so you have a valid primary drive....everything the coil needs to work.


Hello Tom,

Any explanation to the top 'curve' of the coil current ramp ? It must also be correct that it is current limiting ?
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Re: Ignition

Postby Autonerdz » Wed Oct 31, 2012 4:14 pm

It must also be correct that it is current limiting ?


Yes. That's an excess dwell coil driver so it has a current limiting feature. This also accounts for the primary voltage drop you were concerned about.
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