Ignition System - HEI-Est (CALIF): Description

The Delco-Remy HEI-EST system, a part of all General Motors Computer Command Control (CCC) systems, is designed to provide optimum performance through electronic control of air/fuel ratios, spark timing, air management and idle speed.

The system consists of an electronic control module (ECM), an HEI-EST distributor, an external ignition coil, and necessary wiring. The distributor has neither vacuum nor centrifugal advance mechanisms. See Fig 1 and Fig 2.

The distributor contains a 7-terminal HEI-EST electronic module, a timer core, pole piece, pick-up coil, and a radio noise suppression capacitor.

Fig 1: Disassembled View of EST Distributor. Distributor works with an external ignition coil.

Fig 2: Components of an HEI-EST Distributor. Timer core and pole piece have one tooth per cylinder.

The distributor is connected to the EST system by means of a 4-wire connector, leading to the CCC system's electronic control module (ECM).

The ECM (not the distributor HEI-EST module) receives voltage signals from a number of sensors. A typical system could be provided signals from oxygen, engine coolant temperature, throttle position, barometric pressure and manifold absolute pressure sensors, as well as, the distributor pick-up coil.

CAUTION: Few components are interchangeable between HEI-EST and HEI distributors used on various engines. Be sure correct part is used, as similar appearance does not mean identical design or operation.

The HEI-EST distributor module has 7 terminals. The ignition coil battery terminal (positive) is connected to the module "+" terminal; the coil's "TACH" or negative terminal to the "C" terminal. See Fig 3.

Terminals "N" and "P" are attached to the pick-up coil. HEI-EST module terminal "R" connects through the EST connector "B" to ECM terminal 10 (Distributor Reference Pulse Hi). Terminal "B" connects through terminal "C" to ECM terminal 11 (Ignition Module By-Pass).

Terminal "E" connects through connector "A" to ECM terminal 12 (EST). ECM terminal 13 (Distributor Reference Pulse Lo) connects to connector "D" and then to HEI-EST module ground.

Fig 3: Schematic of HEI-EST Ignition System. Upper left illustration corner shows actual shape of HEI-EST module.