Capturing secondary ignition

Albin Diagnostician Leavenworth, Washington Posted   Latest   Edited  
Discussion
Driveability
2000 Nissan Xterra SE 3.3L (VG33E) 5-spd (RS5R30A)
Known Good

This vehicle is running correctly. I wanted to take the time and do a demonstration on capturing a secondary ignition waveform, then explain what it is and how it works. I am using my Pico scope, with secondary leads from AES wave. Here's a video I created:

Once the data has been captured, you need to save the file for later viewing. I want to start off by explaining the different parts of the secondary waveform.

The secondary voltage waveform shape is caused by the resistance in the secondary ignition system. In the secondary ignition, there are two different types of resistance, fixed and variable. The fixed resistance is anything between the ignition coil & the spark plug gap. This includes the distributor rotor cap in most cases, the secondary plug wires and the resistance of the spark plug.

The variable resistance happens in the plug gap. This resistance is controlled by the compression & the HC that is in the plug gap. If the AF mixture is rich (abundance of fuel), the resistance to current flow will be low, and the firing line will be sloping down. If the AF mixture is lean ( abundance of oxygen), then the resistance is high and the firing line will be sloping upward.

The sharp rise at the end of the firing line is the nose. This is caused by the HC in the plug gap being depleted, which causes the resistance in the plug gap to rise, thus the rise in voltage. This is saying the ignition coil is capable of storing more energy than is required to keep the fire lit in the plug gap and is capable of burning the HC in the plug gap. A good nose is good.

diag​.​net/file/f4u9iqy1n…

Once the waveform is captured and stored, then it is easy to open the file and play with it. This file has captured everything from idle, snap throttle, deceleration and back to idle. Now it is easy to pick out the part that you want to analyze. In this case I have zoomed in on the portion of the throttle snap where the engine started gulping air.

diag​.​net/file/f7ia4w08e…

To see the raw Pico file, you can find it here.

+13
Bill Technician
Rosetown, Saskatchewan
Bill
 

Impressive explanation. Really got the meat and potatoes into a short write up. Thank you.

+1 Ð Bounty Awarded
Josh Technician
Lynchburg, Virginia
Josh
 

Very nice write up. Thanks for sharing

0 Ð Bounty Awarded
Dmitriy Analyst
Toronto, Ontario
Dmitriy
 

Albin, great practical presentation. However, there are some concepts (or their wording?) that I can't quite capture the meaning of. Could you clarify what is meant by - Paragraph 3: the resistance in the energy (stored in the ignition coil); - Figure 1: Firing line, first half in the secondary, second in the plug. What kind of half of the line -- left, right?

0 Ð Bounty Awarded
Albin Diagnostician
Leavenworth, Washington
Albin
 

Is this the paragraph you are referring to? "The sharp rise at the end of the firing line is the nose. This is caused by the HC in the plug gap being depleted, which causes the resistance in the plug gap to rise, thus the rise in voltage. This is saying the ignition coil is capable of storing more energy than is required to keep the fire lit in the plug gap and is capable of burning the HC in

0 Ð Bounty Awarded
Dmitriy Analyst
Toronto, Ontario
Dmitriy
 

Not that paragraph, the one right under Figure 1: "The secondary voltage waveform is shaped and caused by the resistance in the energy stored in the ignition coil and the resistance in the secondary ignition system" For Figure 1, I have heard "Firing line" referred to the vertical spike, while the flat section got called Spark or Burn line. Aren't these definitions standardized? For the

0 Ð Bounty Awarded
Geoff Diagnostician
Lahaina, Hawaii
Geoff
 

Dmitriy asked; "For Figure 1, I have heard "Firing line" referred to the vertical spike, while the flat section got called Spark or Burn line. Aren't these definitions standardized?" Agreed, sir. I have always seen "firing line" to be the straight-up part also. like this;

0 Ð Bounty Awarded
Albin Diagnostician
Leavenworth, Washington
Albin
 

I fixed it.. Thanks for the pointer

+1 Ð Bounty Awarded
Angel Technician
Boston, Massachusetts
Angel
   

Great write up, thank you for sharing with us your tips and techniques.

0 Ð Bounty Awarded
Chris Diagnostician
Commack, New York
Chris
 

Thanks Albin, this was very helpful.

0 Ð Bounty Awarded