ECM Code EO23, Est Circuit Problem: Action:
ECM turns on SERVICE ENGINE SOON light and will not enable spark timing control. The engine will start and run on base timing.
Test Number 1) When circuit No. 423 is shorted to ground, engine will have a long crank and hard start. When ECM detects grounded circuit, by-pass line will be shifted low.
Test Number 2) With only distributor reference and distributor reference ground jumpered, engine will run on back-up spark control. This checks for proper ground connections between ECM and engine, and ECM and HEI.
Test Number 3) This step ensures ECM provides EST output signal over circuit No. 423.
Test Number 4) This checks if HEI module can ground EST signal with an open by-pass circuit.
Test Number 5) This checks if HEI module can recognize a voltage on by-pass circuit and stop grounding EST (ECM-controlled timing).
6) This checks for by-pass signal to module. If by-pass signal is being sent by ECM to HEI, and if module is interpreting by-pass voltage correctly, then module will switch off ground to EST.
7) If chart leads to EST CIRCUIT IS OK, then a fault may exist in the 6-way connector. Check connector and terminals for damage. If connector is okay, plug in connector and retest for Code EO23.