Ignition Control Module -Running

Ignition Control Mode (running mode)

When the RPM exceeds 400, the ECM considers the engine running and applies 5 volts on the by-pass at terminal “B”. This energizes the “relay”and causes the contact to open, this un-grounds the IC line and connects it to the base of the transistor. This switches ignition control to the ECM. Now the ECM is sending the trigger signal tothe base of the transistor over the IC circuit and controlling the firing of the ignition coil primary circuit.

The Ref Lo signal at terminal “G”is a ground. This is the low current ground or return back to the ECM for the electronics in the IC module. The high current that comes from the ignition coil gets grounded through the module mounting bolts. It is important that there is a good ground through these bolts. A poor ground will result in a poor running engine.

See page 4-6 in the “EF”manual or pages 38 and 39 of 742218 manual for results of incorrect operation such as an open IC line or grounded IC line,etc.

MEFI 3 Ignition System

The ignition coil has 2 connectors, one black and one gray. The black connector has the power feed back to the ignition module and the ignition coil primary ground circuit. The power feed to the ignition module is pink and the primary groundis brown. The gray connector contains the power feed for the ignition coil and the tach lead. The power feed for the ignition coil is purple and the tach lead is gray. The purple wire is the output from the ignition relay.

Current flows into the ignition coil through the purple wire, through the primary winding and on to the ignition module via the brown wire. Current is also supplied out of the coil on the pink wire to power up the IC module. The IC module high current ground is through the mounting bolts. Loose mounting bolts can cause a poor running engine due to weak spark. When the IC module grounds the brown wire the coil is saturated and builds up a large magnetic field. When the IC module or the ECM want to fire the ignition coil, the IC module shuts down the current flow in the primary and that induces a high voltage into the secondary winding that is supplied to the distributor.