Beginning of energy accumulation in the ignition coil's magnetic field (coincides with the moment the breaker contacts close)
Breakdown of the spark gap between the spark plug electrodes and the beginning of the spark (coincides with the moment the breaker contacts open)
Spark combustion section.
End of spark combustion and the beginning of damped oscillations

Waveform_contactless_transistor_ignition

Figure 5. High-voltage pulse waveform from a contactless transistor ignition system

The start of energy accumulation in the ignition coil's magnetic field, coinciding with the opening of the commutator's power transistor
The breakdown of the spark gap between the spark plug electrodes and the start of spark combustion, coinciding with the closing of the commutator's power transistor
Spark ignition section
End of spark ignition and the beginning of damped oscillations
The commutator's transition to current limiting mode in the ignition coil's primary winding at 6...8 A.

The USB Autoscope software allows you to simultaneously monitor all ignition pulses. PlugIn Ignition diagnostics:

The ignition system's operation is described here

2. Typical ignition system faults

This document describes in detail cases of ignition system malfunction.

Let's look at several practical examples of malfunctions provided by owners of the USB Autoscope motortester.

Waveform library from the forum with detailed descriptions of malfunctions

Malfunction examples from the forum:

Spark plug insulator breakdown fault

Malfunction: Burning time before and after replacing the coil

Malfunction of the ignition system distributor

Malfunction breakdown outside the combustion chamber of cylinder №3

3. Adjusting the ignition timing

The main faults in the ignition system are incorrect ignition timing.

Ignition timing correction under heavy engine loads is mechanically controlled by a centrifugal regulator, which adjusts the ignition advance angle based on the stiffness of the springs and the mass of the flyweights, depending on the engine crankshaft speed.

When the engine load changes while its speed remains constant, the centrifugal regulator does not alter the ignition advance, even though under these conditions (constant speed and variable load) the ignition timing should change. To compensate for this, the centrifugal regulator is supplemented with a vacuum regulator.

In the past, ignition timing adjustment was checked using a stroboscope.

Autoscope technology allows this measurement process to be fully automated.

Proper ignition timing adjustment contributes to:

Increased power: Improved acceleration dynamics and higher top speed
Increased torque: Facilitates acceleration and overtaking
Reduced fuel consumption: With optimal components, it can provide fuel savings
Correction of factory errors: Correction of manufacturer-inherent faults

Figure 6. Distributor

Ignition timing testing using USB Autoscope IV and Px script

4. Engine diagnostics using a cylinder pressure sensor. Script Px

Until recently, checking the mechanical condition of an engine required a lot of time and attention.

Here’s an incomplete list of what had to be inspected:

Valve timing phases
Alignment marks of the crankshaft and camshaft
Intake and exhaust valve clearances
Camshaft lobe wear
Shaft runout in support bearings
Cylinder compression
Condition of intake and exhaust valves

Now, Autoscope technology has made this entire process completely automated.

Px v3.24 Script — analyzes key parameters of the cylinder, intake and exhaust systems, valve timing mechanism, and ignition timing control system.

The primary purpose of the Px script is to test the engine's mechanical components and verify the proper operation of its subsystems. The script operates by automatically analyzing the cylinder pressure graph obtained using a sensor installed in place of the spark plug.

5. Reference Px Graphs – Cylinder Pressure Waveform Catalog

This forum thread about Cylinder Pressure Graphs on InjectorService.com.ua is dedicated to creating a structured catalog of reference cylinder pressure waveforms (Px).

The thread includes good reference waveforms, forum users contribute by uploading .mwf files of pressure waveforms and discussing results for engines from various car brands and models, forming a collaborative technical database for automotive diagnostics.

Classic cars diagnostics

In this Article:

Autoscope Technology makes it possible to test and diagnose faults in almost all vehicles produced in the 20th century.

These are vehicles that used a carburetor-based fuel delivery system.

The ignition system in such cars is a contact-type system with a mechanical distributor. Its main components include the ignition switch, battery, ignition coil, capacitor, contact breaker, distributor, and spark plugs.

Although this classic system is simple, it is less reliable than modern electronic systems due to rapid contact wear, which can cause starting issues, power loss, and increased fuel consumption.

1. Ignition system diagnostics

Figure 1. Conventional ignition system diagram with a mechanical contact breaker

Figure 2. Contactless transistor ignition circuit diagram

Figure 3. Connecting capacitive probes for ignition system diagnostics

Figure 4. High voltage pulse waveform of a classic ignition system with a mechanical contact breaker