Testing Coil On Plug (COP) Ignition - best methods?

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Testing Coil On Plug (COP) Ignition - best methods?

Postby Alan » Sat Feb 11, 2012 8:13 am

I was asked yesterday if there is a recommended method / strategy for testing coil on plug (COP) ignition. I have not really thought about it before as the approach varies a bit depending on the symptom (eg no code misfire) and also the vehicle (ease of access to components). Having said that I do tend to follow the same approach and I was wondering if others do the same or have better ways of doing it.

This is my approach for testing COP ignition.

1. Test the secondary signal.
Unless access is difficult I will use the COP probe to fist look at the secondary waveform. If the secondary looks OK then pretty much everything else such as the coil itself, supply, switching etc will be OK. The secondary waveform also contains more information than other methods - with practice you can spot fouled plugs, lean cylinders etc. Most times you can look at all cylinders in a couple of mins if its an easy problem such as a misfire at idle.

Tip: I usually right click and keep the waveform from the first cylinder on screen as a reference to compare against the others, if one cylinder looks different to the other then that is the one to investigate.


COP sec.jpg



2. Test the primary current. (If access to the coils is difficult I sometimes do this first).
I prefer to test all ignition coils at the same time by putting the current clamp around the 12V feed, often the fusebox is a good option, but you have to be careful if the fuse is shared with other components.

cop primary current.jpg


I often use a second clamp at this point and also look at all the injectors at the same time. (I have a bit of a reputation for trying to diagnose everything using a current clamp from the fusebox :lol:)

Tip: If you look at both injectors and ignition and find that both are missing for one cylinder it may be that due to an ignition problem the ECU has disabled the injector for that cylinder to prevent unburnt fuel damaging the catalytic converter. Key off / on and look at the pattern in the first few seconds of running.

One advantage of the above two tests is that they apply regardless of whether you are working with a 2, 3 or 4 wire COP. If however the above tests show a problem on a specific cylinder then the next step becomes component specific but in all cases involves back probing all the wires.

3. Test for 2 wire COP

With these coils the switching is done at the ignition amplifier which can be a separate module or built into the ECU. Some ECUs use the inductive primary kick as a test that ignition occurred so a failed coil can set a code.

Channel A - switching (ie primary voltage)
Channel B - 12V feed (just to check its there / not dropping out)

Tip: If access is difficult at the coil then the switching signal can be measured from the ignition amplifier or ECU. That way the signals for all cylinders are at the same place.

Bonus tip: Many Ford (and some others) 2 wire COP systems multi strike at low RPM for emissions reasons.

4. Testing for 3 wire COP

Three and four wire COPs have the ignition amplifier built in so there is no access to primary voltage. The ECU triggers the ignition to fire with a (usually) 5V pulse. By integrating the ignition amplifier into the coil reliability is increased and often repair costs reduced (especially in the case of ECUs with built in ignition amplifiers).

Channel A - 5V trigger signal
Channel B - 12V feed (just to check its there / not dropping out)
Channel C - GND (just to check we have a good ground)

Tip: With 3 wire systems the ECU can usually not detect if ignition has occurred, in fact you can usually unplug the coil without the ECU noticing. This is in some ways a backward step from a diagnostic point of view over 2 wire coils. If the ECU can detect ignition problems it is using the amplitude of the trigger pulse to detect if the circuit has gone open circuit or shorted.

The example below is from a 3 wire COP, it has primary current included as well. I tend to split the screen into two scopes (right click, Add View) and then put the signals at the top and power / ground at the bottom.

cop 3 wire.jpg


5. Testing for 4 wire COP (with feedback signal)

With a 4 wire COP, the first thing is to work out if its a true 4 wire system with a feedback pulse to the ECU. Other 4 wire systems (most GM ones) have an extra ground from the ECU. Think of these as "3 wire COPs with an extra wire" most of them however can set codes my measuring the amplitude of the trigger signal.

Some 4 wire COPs have 2 grounds, other have a feedback signal to the ECU that gives a pulse when the ignition fires.

Channel A - 5V trigger signal
Channel B - Feedback signal or 2nd ground
Channel C - 12V feed (just to check its there / not dropping out)
Channel D - GND (just to check we have a good ground)

Tip: The feedback signals are wired in parallel from each cylinder to reduce the amount of wiring whilst the trigger signals are individual. Expect to see more feedback signals per engine cycle than trigger. If you see the same number of trigger and feedback signals that may suggest an open circuit in the wiring for that coil.

Bonus tip: To be honest the channel order above does not matter too much. You can usually guess which is which but if you wire it up differently it makes no difference. If you start with a timebase of 20ms/div then you dont need to worry about triggering to start, but you can add a trigger later when you have sorted out which channel is which.

As I said at the start, this is how I do it but I would love to hear from others if they have different & hopefully better ways.
Alan
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Re: Testing Coil On Plug (COP) Ignition - best methods?

Postby Damian Mc Bride » Sun Feb 12, 2012 4:06 pm

Hi Alan keep up the good work your posts are a real help to users like myself.
Would it be possible to include ps data files so we could open them and look in more detail.
Regards Damian
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Re: Testing Coil On Plug (COP) Ignition - best methods?

Postby Alan » Mon Feb 13, 2012 7:03 am

Damian Mc Bride wrote:Hi Alan keep up the good work your posts are a real help to users like myself.
Would it be possible to include ps data files so we could open them and look in more detail.
Regards Damian


Thanks! The secondary waveform and the 3 wire COP ones are taken from the preset waveforms supplied with PicoScope software. I am away from the office this week so the primary current will have to wait unless some kind person wants to upload one.
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Re: Testing Coil On Plug (COP) Ignition - best methods?

Postby Damian Mc Bride » Mon Feb 13, 2012 10:39 am

That grand no panic on.
Regards Damian
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Re: Testing Coil On Plug (COP) Ignition - best methods?

Postby Alan » Wed Feb 15, 2012 7:26 am

Just found a nice youtube video on testing 3 or 4 wire COP. Shows secondary, primary current and trigger signal. Enjoy :D

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Re: Testing Coil On Plug (COP) Ignition - best methods?

Postby IanCrane » Sun Feb 19, 2012 9:36 am

Fabricate an alloy plate that fits over the coil and induce a field into the scope connection
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Re: Testing Coil On Plug (COP) Ignition - best methods?

Postby benmixmaster » Mon Feb 20, 2012 7:20 pm

Hi alen,
I like that tip "Tip: I usually right click and keep the waveform from the first cylinder on screen as a reference to compare against the others,"
I Did not know that feture was so easy to use, Got any more tips on the reference capture, shoot away.

I have the ferret parading cop fuel injection adater , parades up to 10 cylinders or ingectors, pretty cool, but It seems to have wierd effect ypon a snap accel, like it pulls the whole signal off ground but at idle looks pretty good, Kinda weird , But if I find a work around for it, I will try and remember to post it here.

You can use 2 of them the same time and see all injectors on one channel and all cylinders cop ingnition on another channel the other, also you can use its internal sync or an external sync, only one unit or external sync is needed.
thanks for the tip using picoscope right click reference waveform. benmixmaster
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