Ignition System - Hei GMC Vandura I

DESCRIPTION

Note. Some Chevrolet and GMC light truck models with 5.0L 4-Bbl. (VIN LE9) engines are equipped with Electronic Spark Control to combat detonation. ESC models have 5-terminal electronic modules in the distributor, while non-ESC models have 4-terminal modules.

The Delco-Remy High Energy Ignition system consists of a battery, ignition switch, ignition coil, spark plugs, primary and secondary wiring, and a special distributor assembly.

The distributor housing and cap contain vacuum and centrifugal advance mechanisms, an electronic control module, pick-up coil, pole piece (with internal teeth), timer core (with external teeth), rotor, distributor shaft and a capacitor for radio noise suppression. Some distributor models also include an integral ignition coil.

Full battery voltage is present at the battery terminal of the distributor in either the "START" or "RUN" position, as no ballast resistance wire is used.

Exploded View of HEI Distributor Timer core and pick-up coil pole piece have one tooth per cylinder. Scheme 1

OPERATION

The pick-up coil assembly consists of a permanent magnet, a pole piece, and a pick-up coil. The pick-up coil assembly is stationary, unless it is shifted by the vacuum control unit. The timer core position can also be shifted by the centrifugal weights.

The timer core, mounted on the distributor shaft, rotates with the shaft inside the pole piece portion of the pick-up coil assembly.

When the external teeth of the timer core line up with the internal teeth of the pole piece, a voltage is induced in the pick-up coil. This signals the electronic module inside the distributor, which opens the ignition coil primary circuit. (Scheme 2)

Delco-Remy HEI System Wiring Diagram Module terminal letters may vary by model. Scheme 2

The magnetic field in the ignition coil primary circuit collapses, inducing high voltage in the coil's secondary circuit. This travels through the distributor cap contact, rotor and secondary wires to fire the spark plugs.

The electronic module automatically controls dwell period, stretching it with increasing engine speed. Dwell is not adjustable, and periodic checks of dwell are unnecessary. The HEI system features a longer spark duration, which is desirable for firing lean and EGR diluted mixtures.

TROUBLE SHOOTING

Note. See the TROUBLE SHOOTING - BASIC PROCEDURES article in the GENERAL TROUBLE SHOOTING section.

TESTING

Note. To remove spark plug wires, twist boot 1/2 turn and pull on boot (not on wire). When using a timing light, connect at plug end of number 1 spark plug wire ( DO NOT pierce plug boot).

Check that wiring connector is properly attached to connector at side of distributor cap, and that spark plug leads are properly connected at both ends before continuing with test procedures.

ENGINE WILL NOT START

Note. If engine is difficult to start or misses, check position of battery terminal connector at distributor cap. Terminal must be inserted on side of connector opposite hold-down clip.

1. Connect voltmeter between battery terminal lead on distributor connector and ground. Turn ignition switch on. If voltage is zero, check system for open circuit.
2. If reading is battery voltage, connect a modified spark plug (plug that has ground electrode cut off) to center brush contact in distributor cap.
3. Crank engine. If spark occurs, trouble is not in ignition system. Check fuel system, spark plugs and wires for trouble. If sparking does not occur, follow procedures under System Testing or Component Testing. (Scheme 3)

Modifying Spark Plug for Testing A commercial spark tester may also be used. Scheme 3

ENGINE STARTS BUT RUNS ROUGH

1. Check for proper fuel delivery to carburetor, vacuum hoses for leakage, ignition timing, centrifugal advance for proper operation, spark plugs for defects, and visually inspect and listen for sparks jumping to ground or to other wires.
2. If no defects are found or condition continues after correction, follow procedures under System Testing or Component Testing.

Scheme 4

Scheme 5

1. Connect voltmeter positive lead to distributor battery terminal and negative lead to ground. Crank engine. If voltage is under 7 volts, repair or replace wiring or components back to battery, including ignition switch and all connections.
2. If voltmeter reading in step 1) was 7 volts or more, connect positive lead of voltmeter to "TACH" terminal of distributor, while leaving negative lead attached to ground. If voltmeter reading is 10 volts or more, proceed to step 4).
3. If reading in step 2) was under 1 volt, replace ignition coil. If reading was 1-10 volts, replace electronic HEI module in distributor, and check for spark as instructed in step 9). If spark results, system is OK. If no spark results, replace ignition coil in addition to the module.
4. If reading in step 2) was 10 volts or more, remove distributor cap, but leave wiring harness attached to cap connector. Connect spark tester (ST-125) or modified spark plug so terminal touches center contact of cap. Ground tester ground wire, and crank engine. (Scheme 4) (Scheme 4): Checking for Spark at Ignition Coil Output Terminal Integral coil model is illustrated.
5. If spark occurs, inspect cap for water, cracks, or other defects. If cap is OK, replace rotor. If no spark occurred in step 4), remove pick-up coil leads (Green and White wires) from module. Again, check voltage at "TACH" terminal of distributor cap.
6. Attach voltmeter positive lead to "TACH" terminal and negative lead to ground. (Scheme 5) Turn ignition switch on. Attach test light to battery positive terminal.
7. Perform next test with test light still connected to battery positive terminal and Green and White wires still disconnected from module. Momentarily touch other test light lead to module terminal "P". This is the small terminal. Touch light to module for no more than 5 seconds. Observe voltmeter reading. (Scheme 5): Checking Distributor Components with Voltmeter and Test Light Integral coil model is illustrated.
8. If voltage did not drop, check module ground. Also check for open in wires for distributor to cap. If OK, replace HEI module.
9. If voltage dropped in step 5) when test light was connected, or if 1-10 volts was recorded in step 2), check for spark at coil center contact (using spark tester as before) as test light is removed from module's "P" terminal.
10. If spark results, replace pick-up coil assembly. If no spark appears, use module tester to test HEI module. If OK, check ignition coil ground. If ground is OK, replace ignition coil. If module is defective, replace it.
11. If no module tester is available, check ignition coil ground circuit. If OK, replace ignition coil and repeat step 9). If spark results, system is OK. If no spark results, original coil is OK. Replace module.

INTERMITTENT SYSTEM PROBLEMS

1. Using a spark tester or modified spark plug, check for spark at 2 spark plug wires. If no spark results, see System Testing. If spark is noted on one or both wires, check for dwell increase from low to high RPM.
2. Check pick-up coil with ohmmeter leads attached to Green and White wires, removed from HEI module. If reading does not indicate between 500-1500 ohms, replace pick-up coil. If pick-up coil reading was satisfactory, and dwell did not increase, replace electronic module.
3. If pick-up coil was satisfactory, but dwell increased, check fuel, spark plug wires, distributor cap, rotor or spark plugs.

Scheme 6

Scheme 7

1. Remove distributor cap and coil assembly by removing wiring harness connector, battery lead, and cap-to-housing latches. Inspect rotor, cap, and coil assembly for arc-over. Replace parts as necessary.
2. To test coil primary resistance on integral ignition coil, connect ohmmeter leads to battery and "TACH" terminals on distributor cap. (Scheme 6) Ohmmeter reading should be zero or nearly zero. Replace coil if not to specifications.
3. Connect ohmmeter leads to "TACH" terminal and ground, and note reading. Next, test coil secondary resistance by connecting ohmmeter leads to coil secondary contact (cap button) and "TACH" terminal. (Scheme 6) Replace coil only if both readings are infinity. (Scheme 6): Testing HEI Distributor Cap & Coil (w/ Integral Coil) Be sure leads contact proper connections.
4. On external coils, connect ohmmeter leads to battery and "TACH" terminals. (Scheme 7) Primary resistance should read zero or nearly zero. (Scheme 7): Coil Testing Connections with External Coil Touch coil mounting screw for ground.
5. Now connect leads to battery terminal and ground. On high scale, an infinity reading should be indicated. For secondary coil resistance, connect ohmmeter leads to "TACH" and secondary terminals. Ohmmeter should read less than infinite.

Distributor Pick-Up Coil

1. Connect external vacuum source to vacuum advance unit. If vacuum advance unit is inoperative, replace unit. To check pick-up coil for shorts, connect the ohmmeter leads as shown by meter "A" in (Scheme 8).
2. Set on middle scale of meter. Operate vacuum advance through range. Reading should be infinite at all times. If not, replace pick-up coil.
3. To check pick-up coil resistance, connect ohmmeter leads as shown by meter "B" in (Scheme 8). Again use the middle scale. Operate vacuum advance through its range. Ohmmeter reading should be 500-1500 ohms in all advance positions. If readings are not as specified, replace pick-up coil.

Distributor Pick-Up Coil Testing Connections. Scheme 8

Capacitor

Set ohmmeter in x1000 scale. Disconnect capacitor. Touch ohmmeter leads to capacitor terminal and to ground. The needle should move slightly, but very quickly, and return to infinity. Any continuous reading other than infinity indicates defective capacitor.

HEI Distributor Electronic Module

If engine operation remains rough after preceding test procedures are completed, replace the distributor electronic module.

Note. When installing a new HEI module, use silicone lubricant on back of module and on housing under module.

ELECTRONIC SPARK CONTROL (ESC) TESTING

Note. Electronic Spark Control (ESC) is used on some Chevrolet and GMC models using the 5.0L 4-Bbl. (VIN LE9) engine.

Wiring Diagram for HEI Sys. w/Electronic Spark Control (ESC). Scheme 9

Detonation Problems

Note. Before diagnosis, check connection at sensor and ensure that all connections are clean and tight. Occasional detonation is acceptable.

1. Adjust engine to about 1000 RPM. With transmission in Neutral or Park, lightly tap exhaust manifold repeatedly. Check for timing retard with a timing light. If retard is noted, detonation sensor is functional.
2. If no retard occurs, disconnect 10-pin connector from ESC controller, located in passenger compartment. Connect ohmmeter leads between pins "B" and "K" of connector. Ohmmeter should read about 99 ohms. If so, proceed to step 5).
3. If meter reading was incorrect, disconnect detonation sensor wire. Measure resistance from sensor terminal to ground. Reading should be about 99 ohms. If ohmmeter reading is incorrect, replace sensor. If okay, repair wiring circuit from pin "B" to sensor.
4. If ohmmeter reading in step 2) was okay, try to start engine with 4-pin connector disconnected. If it starts, stop engine and attach high resistance test lamp from "TACH" terminal to ground. If lamp lights, and flickers during engine cranking, system is okay. If lamp does not light/flicker, replace ignition module or pole piece.
5. If engine will not start, reconnect 4-pin connector. Disconnect sensor wire from sensor, and insert a jumper wire into sensor wire connector. With engine running at fast idle speed, lay wire on top of distributor over ignition coil. If spark timing retard occurs, replace sensor.
6. If no spark retard occurs, connect voltmeter positive lead to pin "H" of 10-pin connector and negative lead to pin "K". With ignition switch on, voltage should read more than 0.2 volt. If voltage is over 0.2 volt, replace ESC controller. If less than 0.2 volt, repair open wire from pin "H" in ESC harness.

Poor Engine Performance Problems

1. Disconnect 4-pin connector at distributor, and install a jumper wire between pins "A" and "C" of distributor connector. If problem remains, check other causes of poor engine performance.
2. If problem disappeared, remove jumper wire and reconnect 4-pin connector. Without disconnecting 10-pin ESC connector, attach jumper wire from pin "A" to pin "K". If problem remains, proceed to step 5).
3. If problem disappeared in step 2), remove jumper wire and disconnect sensor wire form sensor. Measure voltage from sensor terminal to ground. Minimum reading is 80 millivolts. If OK, check for engine noises other than detonation that might cause input to sensor.
4. If resistance reading was either high or low in the previous step, disconnect wire from sensor. Measure resistance from terminal to ground, checking again for 175-375 ohms. If high or low, replace sensor. If OK, check sensor wire and shield for open circuit. If OK, repair sensor connector. If not OK, repair harness.
5. If in step 2), the problem still existed, remove jumper wire from pins "A" and "K". With engine running, connect positive voltmeter lead to pin "F" and negative lead to pin "K" of 10-pin connector. If reading is under 11.6 volts, repair alternator charging circuit.
6. If over 11.6 volts, check wires in ESC harness from pins "H" and "K" for open circuits or poor connections. If OK, replace ESC controller; if not, replace or repair harness.

Engine Starting Problems

1. Check all ESC harness connections, including 10-pin connector, 4-pin connector at distributor, 2-blade male connector to distributor, and 2-blade female connector to ignition switch lead (Pink wire). Repair as necessary.
2. If all connections are OK, disconnect 4-pin connector at distributor. Install jumper wire between pins "A" and "C" of distributor connector. If engine will not start, check other causes of engine failing to start.
3. If engine starts with jumper wire attached, remove jumper wire and reconnect 4-pin connector to distributor. With ignition switch "ON", connect voltmeter positive lead to pin "F" and negative lead to pin "K" on 10-pin connector. If under 7.0 volts, repair circuit between ignition switch and pin "F".
4. If over 7.0 volts are read, check wires in ESC harness from pins "G", "H", "J" and "K" of 10-pin connector for opens or shorts. If harness is OK, replace ESC controller.

DISASSEMBLY

1. Disconnect wiring harness from cap. Disconnect coil wire. Remove distributor cap and disconnect vacuum hose from vacuum advance unit. (Scheme 10)
2. Mark rotor-to-distributor housing position and distributor housing-to-engine position for reassembly reference. Remove hold-down bolt and remove distributor housing from engine.
3. Remove rotor, two advance springs, weight retainer and advance weights. Mark distributor shaft and gear so they may be assembled in same position. Drive out roll pin from drive gear while supporting gear so no damage will occur to distributor shaft.
4. Remove gear, shim and tanged washer from distributor shaft, and clean any burrs from shaft. Remove distributor shaft from housing. NOTE: DO NOT attempt to service shaft bushings in housing.
5. Remove 2 attaching screws holding module to housing, and position module to disconnect pick-up coil and wiring harness connectors. Remove "C" washer from housing, and lift pick-up coil assembly from advance unit and distributor shaft.
6. Remove 2 attaching screws, and remove vacuum advance mechanism. Disconnect capacitor lead, and remove attaching screw and capacitor. Remove wiring harness from position in distributor housing.
7. For integral coils, remove 3 coil cover attaching screws and lift off cover. Remove 4 ignition coil attaching screws, disconnect coil leads, and remove coil from cap. Remove ignition coil arc seal.

Internal Components of HEI Distributor Number of module terminals will vary between regular and ESC systems. Scheme 10

REASSEMBLY

1. Reverse disassembly procedures, while noting the following: Ensure there is special silicone lubricant between module and distributor base to provide heat transfer for module cooling. Lubricate felt washer with a few drops of engine oil.
2. After installation of distributor shaft, rotate to check for even clearance between external timer core teeth and internal pole piece teeth. Notch on side of rotor must engage tab on cam weight base.

Typical Primary and Secondary Oscilloscope Patterns Refer to instructions by scope manufacturer. Scheme 11

Scope Instructions for Primary Parade Only

Note. Also refer to instructions furnished by scope manufacturer.

1. Scope secondary pick-up cannot be connected on integral coils, because coil center terminal is inside distributor.
2. Connect pick-up to No. 1 spark plug wire.
3. Connect primary pick-up to "TACH" terminal at distributor connector plug. (Scheme 11)

Reading Scope Primary Pattern

1. A) Spark Zone - spark plug arcing.
2. B) Coil & Condenser Zone
3. B1) Firing Zone - no plug arc.
4. C) Dwell Zone - displays current through coil primary with module turned on.

TYPICAL SECONDARY PATTERNS

Note. A special adapter placed on top of the coil cap assembly may be used with some scopes to view the secondary pattern. The output voltage will read low with the adapter; this is normal. Refer to the scope manufacturers' instructions.

Secondary Voltage Patterns

It is normal if dwell time varies from cylinder to cylinder. A 40 to 60 percent variation is shown below. It could be more, or it could be less. The voltage ripple shown may or may not appear; either is normal. Variation in dwell time or voltage ripple, as shown, does not necessarily indicate a bad module. (Scheme 11)

See also:
• TROUBLE SHOOTING - BASIC PROCEDURES