Ignition System - Hei (federal) GMC Value Van P2500

DESCRIPTION

The Delco-Remy High Energy Ignition (HEI) system consists of the ignition coil, spark plugs, distributor assembly and primary and secondary wiring.

The distributor housing contains an electronic control module, pick-up coil, pole piece, timer core, rotor, capacitor for radio noise suppression and timing advance mechanisms. Most applications house the ignition coil assembly within the distributor cap. (Scheme 1) Full battery voltage is present at the battery terminal of distributor cap in either the "START" or "RUN" position. Ballast resistance is not used in the primary system.

Chevrolet and GMC light trucks with 5.0L 4-Bbl. (VIN H) engines are equipped with Electronic Spark Control to suppress detonation. ESC models have 5-terminal electronic modules in the distributor and non-ESC models use 4-terminal modules.

Exploded View of HEI Distributor. Scheme 1

OPERATION

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

When timer core external teeth line up with internal teeth of pole piece, voltage is induced in the pick-up coil. This signals the electronic module to open ignition coil primary circuit. (Scheme 9) This causes low voltage in the ignition coil primary circuit to collapse and induce high voltage while traveling across coil secondary windings. Voltage travels through the rotor, distributor cap and secondary wires to fire each spark plug.

The electronic module controls dwell period and is not adjustable. Periodic checks of dwell are unnecessary. The HEI system features a longer spark duration, which is desirable for firing lean and EGR-diluted mixtures.

SYSTEM TESTING

The following precautions MUST be observed during testing procedures

1. DO NOT ground distributor tachometer connector. Damage to the ignition coil or module can result.
2. Disconnect ignition switch connector at distributor before making compression checks.
3. When using a timing light, attach at plug end of No. 1 spark plug wire. DO NOT pierce plug boot.
4. To remove spark plug wires, twist boot 1/2 turn and pull on boot (not on wire).

1. Prior to diagnosis of HEI system, visually inspect spark plug wires, plug wire boots, rotor contact button (both sides), rotor and distributor cap. If damaged or worn, replace unit(s).
2. Verify wiring connector is securely attached to distributor cap. Ensure plug wires are connected at both ends before continuing test procedures.
3. 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 ignition or pick-up coil.

ENGINE WILL NOT START

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

Scheme 2

1. Check spark at plug using Test Plug (J-26792), while cranking engine. (Scheme 3) If no spark occurs, check another wire. If a few erratic sparks occur, it is considered no spark. If spark occurs, check fuel system and spark plugs.
2. If no spark occurs, separate 4-terminal EST connector (if computer equipped). If engine starts, check computer memory for trouble codes. If not, 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 one volt, replace ignition coil. If reading is from one 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 2) If spark occurs, check cap and rotor for damage. (Scheme 2): Testing for Spark at Coil Output Terminal
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 (BAT.+) (NOT OVER 5 SECONDS). (Scheme 4)
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 occurs, use a module tester and follow instructions. If module tester is not used, check ignition coil ground circuit.
8. If okay, replace ignition coil and repeat check for spark from coil as outlined in step 6). If spark occurs, system is okay. If no spark occurs, install original coil and replace module.

Modifying Spark Plug for Testing. Scheme 3

Distributor Component Testing. Scheme 4

INTERMITTENT SYSTEM PROBLEMS

1. Check spark at 2 plug wires using test plug. If no spark occurs, refer to «ENGINE WILL NOT START»(/gmc/value-van-p2500/1985-1987/remont/ignition-system/#ignition-system-hei-federal__engine-will-not-start) section. If spark occurs from one or both spark plug wires, check pick-up coil with ohmmeter. Refer to «PICK-UP COIL»(/gmc/value-van-p2500/1985-1987/remont/ignition-system/#ignition-system-hei-federal__pick-up-coil) in COMPONENT TESTING section in this article.
2. Replace pick-up coil if defective. If unit test good, check for dwell increase from high to low RPM. If dwell did not increase, replace electronic module. If dwell did increase, and trouble is not found, check fuel, coil and plug wires, also cap and plugs.

ELECTRONIC MODULE

1. An approved electronic module tester must be used to test the module. Use Module Tester (J-24642-E). Follow manufacturer's instructions.
2. When installing a new HEI control module, use silicone lubricant on module-to-distributor housing contact surface to assist heat dispersement.

Chevrolet & GMC Only

1. Connect an ohmmeter between the negative terminal and the high voltage terminal. (Scheme 5) Use high resistance scale. If ohmmeter does not indicate below infinite resistance, coil must be replaced.
2. Connect ohmmeter between the positive terminal and coil frame (ground). Use the high resistance scale. If ohmmeter does not indicate infinite resistance, replace coil.
3. Connect 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.

Integral Coil Test Connections. Scheme 5

EXTERNAL IGNITION COIL

1. Connect ohmmeter leads to battery and "TACH" terminals. (Scheme 6) Primary resistance should read approximately zero. Attach leads to battery terminal and ground. An infinite reading indicates coil is okay.
2. Connect ohmmeter leads to "TACH" and high voltage terminal. Use high resistance scale. If ohmmeter does not indicate below infinite resistance, coil must be replaced. (Scheme 6)

External Coil Test Connection. Scheme 6

PICK-UP COIL

Note. Activation of the vacuum advance may align trigger wheel tooth and pick-up coil pole piece causing ohmmeter pointer to deflect. This deflection should not be diagnosed as a faulty pick-up coil.

1. Isolate 2 pick-up coil lead wires. Remove pick-up coil connector from module. Connect ohmmeter to either terminal and ground. (Scheme 7) Connect pump and apply vacuum to test to vacuum advance unit. Replace vacuum advance unit if inoperative.
2. Attach ohmmeter to either pick-up coil terminal and the distributor housing. Select mid scale. Operate vacuum pump and observe ohmmeter throughout vacuum range. Reading should be infinite at all times. If not, replace pick-up coil. See meter "A" in Fig. (Scheme 7).
3. Attach ohmmeter to both pick-up coil connector terminals. Operate vacuum pump and observe ohmmeter throughout the vacuum range. Replace coil if reading is not infinite at all times. See meter "A" in Fig. (Scheme 7).
4. Connect ohmmeter to pick-up-coil terminals. Operate vacuum pump and observe ohmmeter throughout the vacuum range. Flex terminal wires by hand to check for possible intermittent defects in wiring or connectors. Replace pick-up coil if resistance is not 500-1500 ohms at all times.

Pick-Up Coil Test Connections. Scheme 7

CAPACITOR

The capacitor is used for radio noise suppression. Set ohmmeter at x1000 scale. Disconnect capacitor. Touch ohmmeter leads to capacitor terminal and ground. Slight needle movement will occur rapidly and return to infinity. A continuous reading other than infinity indicates defective capacitor.

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

1. Disconnect the 4-pin controller at the distributor and jumper pins A and C together at distributor connector. Test drive vehicle. If trouble remains, check for other possible causes. Refer to the «TROUBLE SHOOTING - BASIC PROCEDURES»(/gmc/value-van-p2500/1985-1987/remont/basic-trouble-shooting/#basic-trouble-shooting-general-information) article. If trouble is gone, proceed to step 2).
2. Turn engine off, remove jumper and reconnect 4-pin connector. Disconnect 10-pin connector from controller. Make sure terminals are seated in connector and connection to controller is good. Check connector pins B and K for open or short circuits. Repair circuits as necessary.
3. With multimeter J-29125-A set on DC in 2000 range, check resistance from pin B to pin K. Should read approximately 98-99 ohms. If initial reading is correct, go to step 4). If reading is not correct, disconnect sensor wire from sensor. Check resistance from terminal on sensor to ground. Should read approximately 98-99 ohms. If reading is correct, repair circuit from sensor to pin B. If reading is not correct replace sensor.
4. Reconnect connector to controller. Measure voltage from connector pin F wire to connector pin K wire with engine control switch on.
5. If reading is over 11.6 volts, measure voltage from pin H wire to pin K wire with engine control switch on and voltmeter on the AC, 20 range. Should be more than 0.2 volts. If reading is under 11.6 volts, repair circuit between engine control switch and pin F.
6. If step 5) voltage is over 0.2 volts, test drive vehicle. If trouble remains, replace ESC controller. If voltage was less than 0.2 volts, 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 connected, remove jumper wire and attach 4-pin connector to distributor. With ignition on, attach voltmeter positive lead to pin "F" and negative lead to pin "K" on 10-pin connector.
4. If under 11.6 volts, repair circuit between ignition switch and pin "F". If over 11.6 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.

Disassembly

1. Remove wiring harness from cap. Remove distributor cap and disconnect vacuum hose from vacuum advance unit. Mark position of rotor and distributor housing for reassembly reference. Remove distributor housing from engine.
2. Remove rotor, 2 advance springs, weight retainer and advance weights. Mark distributor shaft and gear so they may be assembled in same position. Drive roll pin out of drive gear while supporting gear to avoid damaging distributor shaft.
3. Remove gear, shim and tanged washer from distributor shaft. Clean all components and remove burrs from shaft. Carefully remove distributor shaft from housing. DO NOT attempt to service shaft bushings in housing.
4. Remove 2 vacuum advance attaching screws and remove unit. Disconnect capacitor lead and remove capacitor. Remove 2 attaching screws holding module to housing and remove module. Remove "C" washer from housing. Remove pick-up coil assembly from distributor shaft.
5. Remove wiring harness from position in distributor housing. 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.

Reassembly

1. Reverse disassembly procedures to reassemble. Apply silicone lubricant between module and distributor base to provide heat transfer for module cooling. Lubricate felt washer with a drop 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 OSCILLOSCOPE PATTERNS

Note. A special adapter placed on top of the coil cap assembly is commonly used to view the HEI secondary pattern. Refer to the scope manufacturer's instructions.

Attach scope secondary pick-up and adapter (if equipped). Connect pick-up to No. 1 spark plug wire. Connect primary pick-up to "TACH" terminal at distributor connector plug. (Scheme 8)

READING SCOPE PRIMARY PATTERN

1. Spark Zone - spark plug arcing.
2. Coil and Condenser Zone.
3. Dwell Zone - displays current through coil primary with module activated.

SECONDARY VOLTAGE PATTERNS

It's normal for dwell time to vary from cylinder-to-cylinder. A 40 to 60 percent variation is shown below. It could be more or less depending on application. 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. Scheme 8

SPECIFICATIONS

DISTRIBUTOR - AUTOMATIC ADVANCE SPECIFICATIONS (1) (5)

DISTRIBUTOR - VACUUM ADVANCE SPECIFICATIONS (1) (5)

System Circuit Diagram (Delco-Remy HEI). Scheme 9

Wiring Diagram (HEI System W/ESC). Scheme 10

See also:
• TROUBLE SHOOTING - BASIC PROCEDURES
• ENGINE WILL NOT START
• PICK-UP COIL