Ignition System - Hei (federal) Chevrolet Forward Control P30

DESCRIPTION

Note. Chevrolet and GMC light truck models with 5.0L 4-Bbl. (VIN H) 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 (HEI) system consists of the 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 The timer core & 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 PRECAUTIONS

The following precautions MUST be observed during testing procedures

1. DO NOT ground tachometer terminal of distributor connector. Damage to the electronic module or ignition coil can result.
2. Disconnect ignition switch connector at distributor before making compression checks.
3. When using a timing light, connect at plug end of number 1 spark plug wire. DO NOT pierce plug boot.
4. Remove spark plug wires, twist boot 1/2 turn and pull on boot (not on wire). Prior to diagnosis of HEI system, visually inspect spark plug wires, rotor contact button, plug wires boots, rotor and distributor cap for damage. If a tachometer is connected to the tachometer terminal, disconnect it before proceeding with the test. 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. 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. Intermittent no start condition may be caused by installation of a wrong pick-up coil or ignition coil.

ENGINE WILL NOT START

Note. If a tachometer is connected to the tachometer terminal, disconnect it before proceeding with the test.

Scheme 3

Scheme 4

1. Check spark at plug using Test Plug (J-26792), or equivalent, while cranking engine. (Scheme 3) If no spark is exhibited from first wire, check a second wire. If a few sparks occur, and then nothing, it is considered no spark. If spark occurs, check fuel system and spark plugs. (Scheme 3): Modifying Spark Plug for Testing A commercial spark tester may also be used.
2. If no spark occurs, check voltage at ignition coil "B+" (battery) terminal while cranking engine. If reading is under 7 volts, repair primary wire circuit.
3. If reading is 7 volts or more, check "TACH" terminal voltage with ignition on. If reading is less than 1 volt, replace ignition coil. If reading is from 1 to 10 volts, replace module and check for spark. If spark occurs, system is OKAY. If no spark occurs, replace ignition coil.
4. If reading is more than 10 volts, check for spark at coil output terminal using Test Plug (J-26792) while cranking engine. (Scheme 4) If spark occurs, check cap and rotor for damage. (Scheme 4): Checking for Spark at Ignition Coil Output Terminal Integral coil model is shown.
5. If no spark occurs, remove pick-up coil connector from module. Turn ignition on. With high input impedance voltmeter, observe voltage at "TACH" terminal while test lamp is momentarily connected to module "P" terminal (NOT MORE THAN 5 SECONDS). (Scheme 5)
6. If no drop in voltage occurs, check module ground circuit and for open wires from coil to distributor. If OKAY, replace module. If voltage drop does occur, check for spark from coil with Test Plug (J-26792) as test lamp is REMOVED from module "P" terminal.
7. If spark occurs, replace pick-up coil. If no spark, use a module tester and follow instructions. If no module tester is available, check ignition coil ground circuit. If okay, replace ignition coil. Repeat check for spark from coil as in step 6).
8. If spark occurs, system is okay. If no spark occurs, install original coil and replace module.

Checking Distributor Components with Voltmeter & Test Light Integral coil model is illustrated. Scheme 5

INTERMITTENT SYSTEM PROBLEMS

1. Check spark at 2 plug wires using Spark Tester (J-26792). If no spark occurs, go to «ENGINE WILL NOT START»(/chevrolet/forward-control-p30/1985-1986/remont/ignition-system/#ignition-system-hei-federal__engine-will-not-start) procedure. If spark occurs from 1 or both spark plug wires, check pick-up coil with ohmmeter, Refer to testing pick-up coil in «TESTING - COMPONENT TESTS»(/chevrolet/forward-control-p30/1985-1986/remont/ignition-system/#ignition-system-hei-federal) .
2. If pick-up coil is defective, replace it. If it is good, check for dwell increase from high to low RPM. If dwell did not increase, replace electronic module.
3. If dwell did increase, and trouble is not found, check fuel, coil and plug wires, also cap and plugs.

The following precautions MUST be observed during testing procedures

1. DO NOT ground tachometer terminal of distributor connector. Damage to the electronic module or ignition coil can result.
2. Disconnect ignition switch connector at distributor before making compression checks.
3. When using a timing light, connect at plug end of number 1 spark plug wire. DO NOT pierce plug boot.
4. Remove spark plug wires, twist boot 1/2 turn and pull on boot (not on wire).

ELECTRONIC MODULE

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

An approved electronic module tester must be used to test the module. Use Module Tester (J-24642-E). Follow manufacturer's instructions.

Chevrolet & GMC Only

1. The ignition coil can be tested for shorted and open windings using an ohmmeter. Connect the ohmmeter between the positive terminal and coil frame (ground). Use the high resistance scale. The ohmmeter should indicate infinite resistance. If not, replace the coil.
2. Connect the ohmmeter between the positive and negative terminals. Use the low resistance scale. The ohmmeter should indicate zero, or nearly zero. If not, replace the coil.
3. Connect the ohmmeter between the negative terminal and the high voltage terminal. Use the high resistance scale. The ohmmeter should indicate less than infinite resistance. If not, replace the coil. (Scheme 6)

Coil Testing Connections with Integral Coil Be sure leads contact proper connections. Scheme 6

PICK-UP COIL

Note. Operation of the vacuum mechanism may cause a trigger wheel tooth and the pick-up coil pole piece to align and the ohmmeter pointer to deflect. This deflection should not be interpreted as the result of a faulty pick-up coil.

1. Identify the 2 pick-up coil lead wires. On most applications, these wires are 1 Green and 1 White. The pick-up coil connector must be disconnected from the module, then an ohmmeter is connected to 1 connector terminal and to the distributor housing. Next, the ohmmeter is connected to both terminals.
2. Connect external vacuum source to vacuum advance unit. If vacuum advance unit is inoperative, replace unit. Connect an ohmmeter, using mid scale, to either pick-up coil terminal and the distributor housing.
3. Operate the vacuum pump and observe the ohmmeter throughout vacuum range. Reading should be infinite at all times. If not, replace pick-up coil. See meter "A" in (Scheme 8).
4. Connect ohmmeter to both pick-up coil connector terminals. Operate vacuum pump and observe ohmmeter throughout the vacuum range. Also, flex wires by hand to locate any intermittent defective connections at pick-up coil and at terminals on ends of wires.
5. The ohmmeter should indicate a constant resistance in the 500-1500 ohm range at all times. If not, replace the pick-up coil. See meter "B" in (Scheme 7)

Distributor Pick-Up Coil Testing Connections. Scheme 7

CAPACITOR

The capacitor is used for radio noise suppression. 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.

TESTING - ESC

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

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, backprobe 10-pin connector at ESC controller located in passenger compartment. Connect voltmeter leads between pins "B" and "K" of connector. With engine operating at 2000 RPM, voltage should read 80 millivolts (.08). If voltage is correct, go 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

1. Disconnect 4-pin connector at distributor. 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 from sensor. Measure voltage from sensor terminal to ground. Minimum reading is 80 millivolts at 2000 RPM. If okay, check for engine noises other than detonation that might cause input to sensor. Or, substitute with a known good sensor.
4. If voltage reading was either high or low in the previous step, disconnect wire from sensor. Measure voltage from terminal to ground, checking again. If high or low, replace sensor. If okay, check sensor wire and shield for open circuit. If okay, check sensor wire for an open and repair sensor connector. If not okay, 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 okay, replace ESC controller; if not, replace or repair harness.

ENGINE STARTING PROBLEMS

1. Check all ESC harness connections, including 10-pin connector at ESC controller, 4-pin connector at distributor, 2-blade male connector to distributor, and 2-blade female connector to ignition switch lead (Pink wire). Repair connections as necessary.
2. If all connections are okay, 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 okay, replace ESC controller.

TYPICAL PRIMARY OSCILLOSCOPE PATTERNS

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 tower terminal is inside distributor. See «TYPICAL SECONDARY OSCILLOSCOPE PATTERNS»(/chevrolet/forward-control-p30/1985-1986/remont/ignition-system/#ignition-system-hei-federal__typical-secondary-oscilloscope-patterns).
2. Connect pick-up to No. 1 spark plug wire.
3. Connect primary pick-up to "TACH" terminal at distributor connector plug. see scheme 10

READING SCOPE PRIMARY OSCILLOSCOPE PATTERN

A) Spark Zone-spark plug arcing.

B) Coil and Condenser Zone.

C) Dwell Zone - displays current through coil primary with module turned on.

TYPICAL SECONDARY OSCILLOSCOPE 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 manufacturer's instructions.

SECONDARY VOLTAGE OSCILLOSCOPE 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 8)

Typical Primary and Secondary Oscilloscope Patterns Refer to instructions by scope manufacturer. Scheme 8

DISASSEMBLY

1. Disconnect wiring harness from cap. Disconnect coil wire. Remove distributor cap and disconnect vacuum hose from vacuum advance unit. (Scheme 9)
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, 2 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 9

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. The notch on the side of the rotor must engage the tab on the cam weight base.

Electronic Spark Control (ESC) HEI System Schematic. Scheme 10

See also:
• TROUBLE SHOOTING - BASIC PROCEDURES
• ENGINE WILL NOT START
• TESTING - COMPONENT TESTS
• TYPICAL SECONDARY OSCILLOSCOPE PATTERNS