Engine speed and crankshaft (piston) position are determined by the non-adjustable magnetic position sensor rather than the distributor. This sensor indicates position of top dead center and bottom dead center, as well as engine speed.

The vacuum sensor, mounted permanently on the computer housing, appears identical to vacuum diaphragms found on conventional ignition systems. However, the internal components differ greatly. Attempts to remove the vacuum sensor will break a small diameter wire leading into the computer, rendering it useless.

As the engine operates and the crankshaft flywheel turns, information is received by the computer indicating engine speed and crankshaft position. The vacuum sensor informs the computer of engine load conditions. See Fig 1.

The computer then interprets the information received, and sets the ignition advance ratio. The computer then opens and closes the primary circuit of the ignition coil, causing a build-up and collapse of the coil's magnetic field.

This in turn, causes a voltage surge in the secondary circuit of the coil. The distributor then furnishes spark to the appropriate spark plug in the correct firing order.

Fig 1: Relationship of Computer and Ignition Coil Vacuum sensor cannot be removed from computer.

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

Ignition System - 1.4L: Operation

Use the Manual With the Right Hardware

When to See a Mechanic