Nissan 240SX/Altima 1993-1998 Repair Guide

General Information


The distributor ignition system differs from the conventional breaker points system in form only; its function is exactly the same: to supply a spark to the spark plugs at precisely the right moment to ignite the compressed air/fuel mixture in the cylinders and create mechanical movement.

Located in the distributor, in addition to the rotor, is a spoked reluctor which is pressed onto the distributor shaft. The reluctor revolves with the rotor; as it passes a pickup coil inside the distributor body, it breaks a high flux field, which occurs in the space between the reluctor and the pickup coil. The breaking of the field allows current to flow to the pickup coil. Primary ignition current is then cut off by the Electronic Control Module (ECM), allowing the magnetic field in the ignition coil to collapse, creating the spark which the distributor passes on to the spark plugs.

The ECM detects information such as the injection pulse width and camshaft position sensor signal. Responding to this information, ignition signals are transmitted to the power transistor.

Ignition timing is revised by the ECM according to internally stored data under the following conditions:

At start-up
During warm-up
At idle
During hot engine operation
During acceleration

The knock sensor retard system is designed only for emergencies. Basic ignition timing is programmed within the anti-knocking zone, if recommended fuel is used under dry conditions. The retard system does not operate under normal driving conditions. If engine knocking occurs, the knock sensor monitors the condition. The signal is transmitted to the ECM, which retards the timing to eliminate the knocking condition.