Original Submission by T:
- 1 Bosch EST Circuit:
- 1.1 EST VK:
- 1.2 Operation:
- 1.3 ECU:
- 1.4 ECU Types:
- 1.5 Coil:
- 1.6 Distributor:
- 1.7 Throttle Position Switch:
- 1.8 Manifold Pressure Sensor:
- 1.9 RPM Based Advance:
- 1.10 Overrun Retard:
- 1.11 Limp Mode:
- 1.12 Starter Signal:
- 1.13 Test Wire:
- 1.14 Air Injection Grub Screws:
- 1.15 IC's List:
- 1.16 Part Numbers:
- 1.17 Wiring Diagrams:
- 1.18 Links:
- 1.19 Terms:
Bosch EST Circuit:
A Crank Angle Sensor is mounted at the Rear of the Engine and receives info from three rotating Magnets implanted in the Flywheel (Manual) or welded into the Flexplate (Automatic). The CAS is also called a Speed Sensor.
Electronic Spark Timing was only fitted to Carburettor 6 Cylinder VK Commodores. EFI VK Commodores do not use EST. They use an HEI Distributor with Balance Weights and a Vacuum Advance Module similar to those used in VC, VH, WB 6 Cylinder Engines.
A Digital ECU reads the CAS Pulses as well as information from the Engine such as Manifold Pressure, Coolant Temperature and Throttle Position to calculate Spark Timing for the Engine.
The ECU collects all the information needed to determine the Spark Timing and it's the ECU that triggers the Coil.
EST VK ECU's come in AUTO or MANUAL types. Neithe unit has any control over the Gearbox and they don't even monitor any Gearbox Top Gear Switch. It is most likely that the spark advance plots are different for each Engine.
The EST VK uses the same Coil as WB, VC, VH and VK 6 Cylinder and V8 Holdens the Bosch HEC-716 Coil.
The EST VK uses a special Distributor that has no Balance Weights or Vacuum Advance Module. The Distributor only houses the Rotor Button and the Distributor Cap. It uses a Special Rotor Button.
Throttle Position Switch:
This allows the ECU to determine when the Throttle is closed or open.
Manifold Pressure Sensor:
This Device plugs into the Inlet Manifold and produces a Resistance that changes with the Manifold Pressure.
RPM Based Advance:
RPM based Advance uses information stored in ROM in the ECU. The required Advance for each specific RPM is held as a value which tells the ECU how long to wait once a CAS Pulse has been recieved before the Coil is Triggered. The delay reduces with the increase in RPM. Dynamic Advance is determined by a pressure sensitive device connected to the Inlet Manifold.
When the Throttle is closed the Throttle Position Switch sends an unique signal advising the case. If the Engine is spinning above 900 RPM and the Throttle is closed, 6 degrees of Advance is produced.
Overrun Retard in EST terms results in reduced emissions.
Any time the circuit loses an input or cannot make rational sense of the Sensor Voltages, the B Voltage is forced to a maximum. When this happens the Ignition Timing runs at a static 6 degrees of advance irrespective of the Engine's Speed or Sensor Voltages.
There is also a Starter Signal which the EST Computer responds to. When the Engine is cranking, the advance is forced to 6 degrees.
There is a test wire taped to the wiring harness at the back of the Rocker Cover. Test Mode is activated by connecting this wire to earth. Once this wire is activated the Computer will signal coded information to a dash mounted warning lamp indicating if there is a fault in any Engine Sensor Circuit.
Air Injection Grub Screws:
Submitted by lovemyholden on Sun, 10/06/2007 - 08:41.
By the way those grub screws are 5/8 UNF x 3/4 inch. I just got some the other day. Thought you might like to record that somewhere. Cheers LMH
End of submission by LMH
Integrated Circuits Used in the EST Design
|4011||Quad Dual Input NAND||3|
|4069UB||Hex Inverter, unbuffered version||1|
|4520||Dual BCD Down Counter||1|
|2732||Eprom 4096 bytes||1|
|74LS537||1 of 10 Decoder with Tristate Outputs||1|
|CPU SC85056||Possibly a custom version of a 6809.||1|
|74LS00||Quad Dual Input NAND||1|
|Part Description||Bosch P/N0
|Coolant Temperature Sensor||0 280 130 026||92017805|
| EST ECU Manual
||9 220 066 008||92020763|