Delco-Remy HEI System
4-151 & Federal V6-173 Engines
When performing diagnostic procedures the following precautions should be noted:
1. When disconnecting electrical connector at ignition coil, do not use screwdriver or other tools, as damage to connector may result.
2. Do not connect tachometer terminal to ground, as this may cause damage to ignition coil or ECM.
3. Use care when handling spark plug wires. Also ensure spark plug wires are properly routed.
4. Ensure tachometer and other test equipment is compatible with the HEI system before using.
Fig. 3 Distributor & coil diagnostic test connections:
ENGINE WILL NOT START
1. If equipped, disconnect tachometer electrical lead from tachometer terminal.
2. Using tool No. J-26792, check for spark at spark plug wire.
a. If spark is present, problem is not in HEI system, check spark plugs and fuel system.
b. If no spark is present, check another spark plug wire. If no spark is present, proceed to step 3.
3. Using a suitable voltmeter, check voltage at ignition coil B+ terminal while cranking engine.
a. If reading is under 7 volts, check primary electrical circuit to ignition switch and repair as necessary.
b. If 7 or more volts is present, proceed to step 4.
4. Check for voltage at Tach terminal with ignition switch in the On position.
a. If less than 1 volt is present, replace ignition coil.
b. If between 1 and 10 volts is present, replace ECM and check for spark at spark plug as described in step 2. If spark is present, HEI system is satisfactory. If spark is not present, replace ignition coil, as it is also defective.
c. If voltage reading is more than 10 volts, proceed to step 5.
5. Connect tool No. J-26792 to coil output terminal and check for spark while cranking engine, Fig. 3 (view A).
a. If spark is present, check distributor cap and rotor for damage and replace as necessary.
b. If no spark is present, proceed to step 6.
6. Remove pickup coil electrical connector from module, then place ignition switch in the On position. Connect a voltmeter with a high input impedance to Tach (-) terminal while momentarily connecting test lamp to module P terminal and note voltage reading. Do not leave test lamp connected to P terminal for longer than 5 seconds.
a. If there is no drop in voltage, check module ground and circuit between coil and distributor. If module ground and electrical circuit between coil and distributor are satisfactory, replace module.
b. If a voltage drop is noted, proceed to step 7.
7. Using tool No. J-26792, check for spark at coil output terminal as test lamp is remove from module P terminal, Fig. 3 (view B).
a. If spark is present, replace pickup coil.
b. If a no spark is condition is encountered, proceed to step 8 if module tester is not available. If module tester is available, proceed to step 9.
8. If module tester is not available, check coil ground circuit and repair as necessary. If coil ground circuit is satisfactory, check coil as described under "Component Testing" and replace if defective. If coil is satisfactory, replace module.
9. If module tester is available, check module and replace if defective. If module is satisfactory, check coil ground circuit and repair as necessary. If coil ground circuit is satisfactory, replace coil.
INTERMITTENT ENGINE OPERATION OR MISFIRE
1. Using tool No. J-26792, check for spark at two spark plug wires.
a. If no spark is present, refer to "Engine Will Not Start."
b. If spark is present, proceed to step 2.
2. Perform pickup coil test as described under "Component Testing."
a. If defective, replace pickup coil.
b. If pickup coil is satisfactory, refer to step 3.
3. Check for dwell increase from high RPM to low RPM.
a. If a dwell increase is noted, HEI system is satisfactory, check ignition wire, distributor cap, rotor, spark plugs and fuel system.
b. If a dwell increase was not noted, replace module.
California V6-173 Engines
Refer to "General Motors Corp. Section" for diagnostic procedures on models equipped with Electric Spark Timing (EST).