DESCRIPTION
The Delco-Remy High Energy Ignition (HEI) system consists of 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 "START" or "RUN" position. Ballast resistance is not used in the primary system.
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 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 2) This causes low voltage in ignition coil primary circuit to collapse and induce high voltage while traveling across coil secondary windings. Voltage travels through 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 is unnecessary. The HEI system features a longer spark duration, which is desirable for firing lean and EGR-diluted mixtures.
Scheme 2
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
- DO NOT ground distributor tachometer connector. Damage to ignition coil or module can result.
- Disconnect ignition switch connector at distributor before making compression checks.
- When using a timing light, attach at plug end of No. 1 spark plug wire. DO NOT pierce plug boot.
- To 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, plug wire boots, rotor contact button (both sides), rotor and distributor cap. If damaged or worn, replace unit(s). Verify wiring connector is securely attached to distributor cap. Ensure plug wires are connected at both ends before continuing 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 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 3
Scheme 4
- Check spark at plug using Test Plug (ST-125), 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.
- 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. 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.
- If reading is more than 10 volts, check for spark at coil output terminal using Test Plug (ST-125) while cranking engine. (Scheme 4) If spark occurs, check cap and rotor for damage.
- 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 light is momentarily connected to module "P" terminal (NOT OVER 5 SECONDS). (Scheme 5)
- 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 (ST-125) as test light is removed from module "P" terminal.
- 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.
- 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.
Scheme 5
INTERMITTENT SYSTEM PROBLEMS
- Check spark at 2 plug wires using test plug. If no spark occurs, refer to «ENGINE WILL NOT START»(/gmc/pickup-r1500/1987-1987/remont/ignition-system/#ignition-system-hei-carbureted-models__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/pickup-r1500/1987-1987/remont/ignition-system/#ignition-system-hei-carbureted-models__pick-up-coil) in COMPONENT TESTING section in this article.
- Replace pick-up coil if defective. If unit tests 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, and cap and plugs.
ELECTRONIC MODULE
- An approved electronic module tester must be used to test the module. Use Module Tester (J-24642-E). Follow manufacturer's instructions.
- When installing a new HEI control module, use silicone lubricant on module-to-distributor housing contact surface to assist heat dispersement.
IGNITION COIL
- Connect an ohmmeter between the negative terminal and the high voltage terminal. (Scheme 6) Use high resistance scale. If ohmmeter does not indicate below infinite resistance, coil must be replaced.
- Connect ohmmeter between the positive terminal and coil frame (ground). Use the high resistance scale. If ohmmeter does not indicate infinite resistance, replace coil.
- Connect ohmmeter between positive and negative terminals. Use low resistance scale. Ohmmeter should indicate zero to one. If not, replace coil.
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.
- 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 vacuum advance unit. Replace vacuum advance unit if inoperative.
- Attach ohmmeter to either pick-up coil terminal and 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).
- 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).
- 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.
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.
Disassembly
- 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.
- 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.
- 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.
- 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.
- 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
- 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.
- 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
- A) Spark Zone - spark plug arcing.
- B) Coil & Condenser Zone .
- C) Dwell Zone - displays current through coil primary with module activated.
SECONDARY VOLTAGE PATTERNS
It is 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. A variation in dwell time or a voltage ripple, as shown, does not necessarily indicate a bad module. (Scheme 8)
