Primary Ignition Coil Renault Megane

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Primary Ignition Coil Renault Megane

Postby Peter704070 » Thu Mar 18, 2010 7:00 pm

Hello

I work at a motor vehicle college and trying to get students to use scopes, some enjoy it and most get confused.

We recently re-built a Renault Megane 1.6 DOHC engine after a camblet failure, the students really enjoyed it.

The car runs fine and pulls fine with out missing a beat, but at idle and sitting in the car it feels like its hunting, but the engine is fine.

The group had a few hours spare today and wanted to scope the vehicle. We did a compression test with the scope and the standard way, the results were fine. We then looked at the injectors with the BEMF the same on all four.

Then we looked at the coils, as each one is individual it gave us a great opportunity to see what voltage each one produced on the primary side.

I have included the pictures but what we cannot understand is why one coil peaks at above 350 volts and the other only reaches 220 volts. We swapped them around to different cylinders expecting the voltage to be the same for that coil but they had swapped over (The coil previously producing over 350 volts now only produced 220 volts, we checked the plugs and checked the gaps but wondering why the difference in voltages, we wanted to check the secondary side and the current but didn't have time.

Would be great to have some information to give the students as they really got into using it on this car.

Thanks Pete
Attachments
Coil Number 1 Renault Megane.jpg
This coil was then fitted to cylinder number one and produced a lower voltage of 220v (I didn't swap the plugs though)
(35.48 KiB) Downloaded 48 times
Coil Number 2 Renault Megane.jpg
This coil was then fitted to cylinder four and produced a Higher voltage of over 400v (I didn't swap the plugs though)
(35.36 KiB) Downloaded 48 times
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Re: Primary Ignition Coil Renault Megane

Postby jez1342 » Fri Mar 19, 2010 6:58 am

on a lot of these the ignition coils are wired in series with each other, 1 and 4, 2 and 3. so if you had a single cylinder missfire and tried disconnecting each coil in turn to try and find the missing cylinder you will cut out 2 cylinders. stupid really.
i find it easier disconnecting each injector in turn to find the missing cylinders on these.
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Re: Primary Ignition Coil Renault Megane

Postby mapengo » Fri Mar 19, 2010 7:37 am

Hi Pete,

So you're saying that the higher voltage stayed with the cylinder?

It could be anything affecting this voltage, a slightly different compression, the earth path of that particular plug, the plug, a resistance in the wire or connector.

etc etc

Hth

Doc...
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Re: Primary Ignition Coil Renault Megane

Postby Peter704070 » Fri Mar 19, 2010 9:45 am

Thank you for the quick reply, what I want to know is, should the voltage be the same on all cylinders?

Does the patterns look okay to everyone else.

Thanks
Pete
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Re: Primary Ignition Coil Renault Megane

Postby Autonerdz » Fri Mar 19, 2010 3:42 pm

Peter,

Two things I wanted to add here...

First, there is very little, if any, diagnostic value in the primary kick.

Second, it's very fast and, if your scope was not set up with enough sample rate, you would not reliably detect the peak. Your images do not show the settings, so I don't know if that was an issue.

You might enjoy this little movie illustrating how an open or shorted secondary had no effect on a primary kick:

http://www.autonerdz.com/flash/prisec.html

Primary current is the only way to validate the primary drive.


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Re: Primary Ignition Coil Renault Megane

Postby Amechs » Sat Mar 20, 2010 11:49 pm

Hello Peter,
these Renault coils are wired in a unique way(as far as I know),where coils 1&4 and 2&3 are wired in series.
Thus it is a sort of wasted spark system.

If you look closely at your images coil1 gets fully grounded while coil2 doesn't,resulting in a lower kick.

It hurt's your head trying to understand this system.

If you measure the current of any coil,you will be measuring the current of it's companion coil also.

Measuring the secondary side should reflect what is actually happening.

Somebody might pitch in with a wiring diagram to make this clearer,I thought I had one but can't find it.

Hope this helps.
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Re: Primary Ignition Coil Renault Megane

Postby Dave Hill » Sun Mar 28, 2010 5:50 pm

Hi Peter.

I too made some interesting discoveries a while back, when I had a closer look at this Renault ignition system. As already suggested, the reason for the difference in the waveform, between the the paired cylinders [1 & 4] - [2 & 3] is due to the way they are wired. Its a cheap way of achieving a "wasted spark" system.

This really is unforgivable, given that, we have all the hardware necessary to achieve sequential ignition. Sadly the ECU & circuitry has not been designed to take full advantage of the hardware! Weird isn't it?

With the circuit layout as it is, the coils are fired at the end of the exhaust stroke as well as the moment just before TDC (just prior to the compression stroke). Mind you, when you think about it, should we worry? So long as we understand the system then I am happy to deal with the fallout! :D

The circuit layout is as follows... The two coils closest to the gearbox are the only ones that receive a direct feed & the two coils closest to the timing belt are the only ones that are grounded directly. I have not refereed to cylinder numbers, because the French method just adds to the confusion.

Here is a crude diagram describing the wiring layout....


Image

Here is a capture I made that tells the same tale as yours.....

Image

Notice also the lower firing voltage in the coil that doesn't receive a full ground during the charging or dwell period. As Tom points out, the "Primary kick" does not have the same significance of the "Peak KV" that can be seen in secondary ignition analysis.

Cheers

Dave
Last edited by Dave Hill on Sun Apr 11, 2010 5:20 pm, edited 1 time in total.
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Re: Primary Ignition Coil Renault Megane

Postby Peter704070 » Sat Apr 03, 2010 6:38 pm

Hello again

Thank you all for your replies, in our college we try to do a lot with scopes and get the students to know how to set them, up but also what they should be looking for.

The Renault was brought to us with a snapped cambelt, the students re-built it and it drove well.

The only issue was at idle, the engine ran fine with no misfire, but inside the car you could feel a slight rocking.

We did an emissions test and the vehicle flew through it, with no small or erratic changes in any of the gas values.

We tested the fuel injectors with all reaching the same BEMF value. We quickly checked the coils to see what they produced.

What I cant understand is how would you diagnose a fault with these coils, this vehicle had one new coil and three old ones fitted. Should we just check the current flowing in each coil and look to see a build up of 6 amps.

Also if we checked the secondary side of the coil would we again see differences in voltages.

Just want the students to be fully able to diagnose a coil on this system and any further help would be fantastic.

Thank You
Pete
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Re: Primary Ignition Coil Renault Megane

Postby IanCrane » Sun Apr 04, 2010 10:07 pm

So did you find why the fuel mixture is rich?
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Re: Primary Ignition Coil Renault Megane

Postby mapengo » Wed Apr 07, 2010 6:00 am

Hi Peter,

Diagnosing this Renault system is a difficult task for most techs, especially those without scopes, good serial data and everyday familiarity with the system.

This is one time where substituting parts is often cheaper and more cost effective for most garages/techs and the customer.

Unfortunately, fitting aftermarket non-genuine coils leads to premature failure all too often. The coils really have to be genuine parts from the dealer to get any sort of longevity from them.

A quick loook at the misfire counters in live data and substitute the coil/s with misfires.

I carry a couple of these pencil coils in the van, it is just quicker and easier to do this than whip the pico out.

The consensus amongst dealer techs is when one coil goes the others will soon follow therefore they normally advocate replacing all four.

Cheers

Doc...
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