Engine with a working volume of 3.1 liters
General description
1. Electronic control unit ECM (or transmission control unit PCM) controls the ignition timing set by the distributor (setting the ignition timing), through the electronic ignition timing control system EST, which ensures improved engine performance, fuel economy and exhaust gas toxicity control.
2. The EST system consists of the ignition distributor, HEI unit, ECM unit and connecting wires. The contacts of the four wires going to the EST block are marked with letters on its body. The four-pin electrical connector of the distributor is marked with the letters A-B-C-D running from left to right (see illustration 9.1 in chapter 5). These chains perform the following functions:
- a) Contact "A" - EST system. HEI unit enable circuit. The ECM unit learns about the actual ignition advance upon receiving the control signal. From this point on, it begins to set the ignition advance or retard. If the base advance value is set incorrectly, the entire ignition curve will be incorrect.
- b) Contact "B" - distributor control signal. It transmits data about the speed and position of the crankshaft to the ECM.
- c) Contact "C" - bypass. At a rotation speed of approximately 400 rpm, the ECM unit supplies 5 V to this circuit; this signal activates the HEI unit, which begins transmitting ignition timing commands to the ECM. If there is an open or short to ground in the circuit, the system will set code 42, after which the engine will switch to operation at the original ignition timing setting plus a small advance value built into the HEI unit.
- d) Contact "D" - low control signal "mass". This wire in the distributor is closed to "ground"; as a result, there is no voltage drop in the circuit, the presence of which could impair the performance of the motor. If this circuit is broken, engine performance may be impaired.
3. The ECM receives a positive control signal from the distributor containing crankshaft speed and position data. After this, the ECM unit determines the required advance value for the given engine operating conditions and sends a corresponding pulse to the distributor via the EST unit.
Examination
4. When the diagnostic contact "Test" in the electrical contact of the ALDL unit is shorted to ground, the ECM unit will set the ignition advance to the specified value. To check the operation of the EST system, the ignition advance must be checked at 1500 rpm with the diagnostic contact not connected to ground. After that, close the contact to ground (see section 2). If the ignition timing changes at 1500 rpm, the EST system is working properly. Typically, if a fault occurs in the EST system itself, fault code 42 will be generated.
Setting the basic ignition timing
Note: To perform this job correctly, first check the data on the VECI plate.
5. To set the base ignition advance value, locate and disconnect the electrical contact of the ignition timing system (the location of this contact and the color of the insulation of the wire leading to it are shown on the VECI plate).
6. Set the ignition timing according to the VECI plate data. This will store code 42 in the ECM memory. Do not forget to clear the memory after setting the ignition timing (see section 2).
7. More complete information regarding the operations of checking and replacing elements in HEI/EST electronic systems (high power ignition system) и DIS (distributorless direct ignition system) are given in chapter 5.
Engine with a working volume of 3.8 liters
General description
8. The EST system consists of the EST unit, the PCM control unit and connecting wires. The contacts of the wires going to the EST unit are marked on its body with letters from "A" to "P". The contacts of the four-pin connector of the crankshaft position sensor are marked from left to right with the letters ABCD. Since diagnostic work requires special equipment, it should be carried out in a specialized repair shop.