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Home >> Chevrolet >> 1981 >> Corvette Automatic Trans >> Repair and Diagnosis >> Engine Performance >> Ignition System >> DELCO-REMY Electronic Spark Timing (Est) Ignition System >> Testing >> Est Emission System Check
July 1: So it begins. Don't worry, this is not in the correct legal jurisdiction!

Est Emission System Check

  1. If car will not run with distributor connected to EST electronic control module (ECM), leave 4-wire EST connector disconnected at distributor and proceed to step  5).
  2. If car will run with distributor connected to ECM, place shift lever in "PARK" or "NEUTRAL" position. Run engine at fast idle and note timing change as distributor EST connector is disconnected. If timing changes, system is OK.
  3. If no timing change takes place on vehicles with automatic transmissions, allow engine to idle in "DRIVE" position. Note timing change as 4-wire EST connector is reconnected and then disconnected. If change occurs, system is OK. If no change occurs proceed to step 4)  .
  4. If vehicle is equipped with manual transmission and no change occurred in step  2), or if equipped with automatic transmission and no change took place in step  3), allow engine to idle. Check voltage output of MAP or vacuum sensor as vacuum hoses are disconnected and reconnected. If no change occurs, problem is in the vacuum or MAP sensor circuit. If voltage output changes, proceed to next step.
  5. Stop engine and connect a jumper wire from terminal "A" to terminal "B" of distributor side of EST connector. See Fig 1. Start engine, ground "diagnostic test terminal", and connect test light from battery positive terminal to terminal "C" of 4-wire EST connector at distributor.
    Fig 1: Test Light Hookup for Checking EST Emission System
    G09317994Courtesy of GENERAL MOTORS COMPANY
  6. If engine stops, check for open or grounded distributor wire to terminal "A" of EST connector. If wire is OK, replace faulty HEI-EST module or its connectors. If engine runs in step  5), remove jumper wire between terminals "A" and "B" of EST connector.
  7. If engine still runs, check distributor wires for open to HEI-EST module terminal "B". Also check for short between module terminals "R" and "E". If wires are OK, replace faulty HEI-EST module or connectors.
  8. If engine stopped when jumper wire was removed from terminals "A" and "B" of EST connector, remove test light and reconnect distributor to EST system. If EST system is also equipped with electronic spark control (ESC), proceed to ESC SYSTEM CHECK .
  9. If the vehicle is equipped with a straight HEI-EST system (without ESC), and if the complaint is that the car will not start and run with distributor connected to ECM, check for open condition from ECM terminal "U" to ground. Also check for grounded wire to ECM terminal "12" (from HEI-EST module terminal "E" to EST connector terminal "A" to ECM terminal "12"). If wire is OK, replace faulty ECM or ECM connector.
  10. If the vehicle is equipped with a straight HEI-EST system and the complaint is "No Timing Change", check for a Park-Neutral switch that signals ECM when vehicle is in "PARK" (auto, trans.) or "NEUTRAL" (man. trans.) shift position. If none, check for open from ECM terminal "11" to EST connector terminal "C". If wire is OK, replace faulty ECM or ECM connector.
  11. If vehicle has Park-Neutral switch, disconnect it and recheck for timing change as in step  2). If timing now changes, adjust or replace faulty Park-Neutral switch. If no timing change takes place, check for grounded wire from ECM terminal "H" to Park-Neutral Switch.
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