Secondary ignition on vehicles with individual coils

Discuss how to competently carry out diagnostics and repair of engine management systems
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zap
Posts: 19
Joined: Mon Jun 18, 2018 11:59 pm

Secondary ignition on vehicles with individual coils

Post by zap » Thu Mar 07, 2019 11:03 pm

Most of the vehicles I work on have individual ignition coils. I'll usually start by hooking the red Cx leads up to cylinders 1-3, then switching the last clamp between cylinders 3 and 4. This isn't the end of the world, but it would be nice to be able to watch all 4 cylinders at the same time.

Is there a way that I can use the green and the red Cx leads at the same time to do secondary ignition on a non-DIS vehicle, like maybe some way to invert the waveform coming from the green leads within the software?

If there isn't a software function to accomplish this, has anyone done this by modifying the hardware? I assume I could do it by making an adapter that would switch pins 1 and 2 between the green Cx leads and the Autoscope.

Kelvin
Posts: 14
Joined: Sun Mar 01, 2015 10:35 pm

Re: Secondary ignition on vehicles with individual coils

Post by Kelvin » Mon Mar 11, 2019 10:05 am

Yes, signals from the red and green sensors can be combined. Yes, you can make an adapter. This adapter should connect:
- pin 1 of the red sensor connect with pin 1 of the green sensor;
- pin 2 of the red sensor connect with pin 2 of the green sensor.

But, this way of checking individual ignition coils is wrong!
The fact is that the high-voltage output of an individual ignition coil is connected to the secondary winding not directly, but through a HV diode built into the coil. Therefore, the high-voltage pulse waveform taken from the output of the individual ignition coil, is distorted due to the influence of this diode.
For this reason, we do not recommend checking individual ignition coils with DIS sensors; we recommend checking them with Cx-M or Lx-M sensors.

https://youtu.be/N_4GPJaxFOI
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zap
Posts: 19
Joined: Mon Jun 18, 2018 11:59 pm

Re: Secondary ignition on vehicles with individual coils

Post by zap » Tue Mar 12, 2019 3:16 am

Oh, okay. Thank you for the education!

When checking secondary ignition, I try to (when possible) load the engine by power braking. (putting the vehicle in gear and applying the throttle while holding the brakes) Is there a tool or fixture that could be used to hold the Lx-M against the ignition coil during this type of testing?

Kelvin
Posts: 14
Joined: Sun Mar 01, 2015 10:35 pm

Re: Secondary ignition on vehicles with individual coils

Post by Kelvin » Tue Mar 12, 2019 9:01 pm

zap wrote:
Tue Mar 12, 2019 3:16 am
Is there a tool or fixture that could be used to hold the Lx-M against the ignition coil during this type of testing?
No, the Lx-M should be held by the hand.

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