1966 – 1971 Diagnosis ENGINE HARD START OR WILL NOT RUN CONDITION

Reconnect spark plug lead. The problem is not in the primary circuits. Check fuel system, starting circuit, carburetion, also check secondary circuit as described under “Engine Surge or Erratic Miss Condition.”

1. Reconnect spark plug lead.
2. Connect a tachometer between coil positive (+) terminal and the pink wire at the 3-wire connector on left side of firewall (Corvette Dist. Con.).
3. Place selector on 1000 R.P.M. scale, then crank the engine and look for tachometer deflection.

Choose one of the following:

NO DEFLECTION

Make the following tests to determine location of open, short, or abnormally high resistance in circuit.

CIRCUIT RESISTANCE TEST
(Using Voltmeter)

1. Connect voltmeter between ignition coil positive (+) terminal and a good ground location.
2. Turn ignition switch to “ON” position and observe voltmeter reading.

Choose one of the following:

• 0 VOLTS

Indicates an open in ignition circuit between the battery positive terminal and the coil positive terminal. If connections are good, insert a jumper lead between the pink and the white lead at amplifier connector.

READS 0 VOLTS
Indicates an open in the harness to amplifier unit. Repair or replace the harness.

READS 2.5-4.5 VOLTS
Indicates open in amplifier unit. Repair or replace amplifier. (See note)

Note: Components of the ignition pulse amplifier are serviced separately, see Service Manual for component test procedure.

• 0-2.5 VOLTS

Indicates high starting by-pass resistance, high amplifier resistance or shorted coil primary. Move voltmeter lead from coil positive to pink wire at 3-terminal connector at firewall (Corvette Dist. Con.) (use test prod).

METER READS OVER 7 VOLTS
Resistance in amplifier or coil resistance wire too high – repair or replace amplifier (See note)

Note: Components of the ignition pulse amplifier are serviced separately, see Service Manual for component test procedure.

READS LESS THAN 6 VOLTS
Resistance too high in starting by-pass wire. (Spec.: approx. 0.7 ohm)

• 2.5-4.5 VOLTS

This is the correct reading, however, when obtained at this stage of the check on a system that has not been functioning properly it would indicate improper triggering action of the distributor pickup coil or amplifier unit. Perform DISTRIBUTOR CHECK.

Check performance of the distributor pickup coil and the amplifier unit by employing either of the test methods described below.

OHMMETER METHOD

1. Detach distributor connector body from harness connector, and connect an ohmmeter to the distributor leads.
2. Slowly rotate magnetic pickup assembly through full advance travel and read ohmmeter. If reading is not within 500-700 ohms replace pickup assembly.
3. If the reading is within the 500-700 ohm range, disconnect one ohmmeter lead and connect to ground.
4. If reading is less than infinity, replace magnetic pickup assembly.
5. If reading is infinite, repair or replace the installed amplifier unit.

Note: Components of the ignition pulse amplifier unit are not serviced separately – only the complete amplifier unit is available for service replacement.

DISTRIBUTOR SUBSTITUTION METHOD

1. 1. Detach distributor connector body from harness connector and connect a spare distributor to the harness connector.
   2. Connect a tachometer between coil positive terminal and the black/pink wire at the 3-wire connector on the left side of firewall.
   3. With the ignition switch “ON,” turn distributor shaft by hand and observe tachometer.
   4. If tachometer needle deflects, replace magnetic pickup assembly in distributor installed in engine.
   5. If there is no needle deflection, replace the installed amplifier unit.

Note: Components of the ignition pulse amplifier unit are not serviced separately – only the complete amplifier unit is available for service replacement.

• 7-11 VOLTS

Indicates high resistance through coil or poor ground. Add jumper wire from coil negative terminal to ground.

READS 2.5-4.5 VOLTS
Ground wire was open. Repair or replace.

STAYS AT 7-11 VOLTS
Replace coil.

• BATTERY VOLTAGE (11-12 VOLTS)

Indicates open in primary circuit, coil, or ground wire from coil negative terminal. Add jumper wire from coil negative terminal to ground.

READS 2.5-4.5 VOLTS
Ground wire was open. Repair or replace.

STAYS AT 11-12 VOLTS
Coil is open. Replace coil.

DEFLECTION

Pin point the system trouble by performing “Ignition Distributor Check”.
OHMMETER METHOD

1. 1. 1. Detach distributor connector body from harness connector, and connect an ohmmeter to the distributor leads.
      2. Slowly rotate magnetic pickup assembly through full advance travel and read ohmmeter. If reading is not within 500-700 ohms replace pickup assembly.
      3. If the reading is within the 500-700 ohm range, disconnect one ohmmeter lead and connect to ground.
      4. If reading is less than infinity, replace magnetic pickup assembly.
      5. If reading is infinite, repair or replace the installed amplifier unit.

Note: Components of the ignition pulse amplifier unit are not serviced separately – only the complete amplifier unit is available for service replacement.

DISTRIBUTOR SUBSTITUTION METHOD

1. 1. 1. Detach distributor connector body from harness connector and connect a spare distributor to the harness connector.
      2. Connect a tachometer between coil positive terminal and the black/pink wire at the 3-wire connector on the left side of firewall.
      3. With the ignition switch “ON,” turn distributor shaft by hand and observe tachometer.
      4. If tachometer needle deflects, replace magnetic pickup assembly in distributor installed in engine.
      5. If there is no needle deflection, replace the installed amplifier unit.

Note: Components of the ignition pulse amplifier unit are not serviced separately – only the complete amplifier unit is available for service replacement.