Ignition System - Hei-Est Pontiac Firebird III

DESCRIPTION

The Delco-Remy High Energy Ignition (HEI) system with Electronic Spark Timing (EST) is a self contained unit. The distributor consists of the housing, rotor, cap, magnetic pick-up, pole piece and pick-up coil. The ignition coil is contained within the cap except for 4-cylinder engines which have an externally mounted coil. The capacitor is used for noise suppression.

All spark timing changes are controlled by the Electronic Control Module (ECM) and there are no vacuum or centrifugal advance mechanisms. Some models use an electronically controlled ignition retard circuit in the event of engine knocking or detonation. Some distributors with externally mounted ignition coils may be equipped with sealed module connectors. (Scheme 3)

Typical HEI (EST) Distributor Integral coil model is shown. Scheme 1

The ECM induces primary voltage in the coil when the teeth on the timing core align with the teeth on the pole piece. As the timing core teeth pass out of the pole piece field, the primary voltage collapses, inducing the secondary voltage in the coil. The secondary voltage is discharged to the rotor which distributes it to the appropriate terminal. The distributor module may have 3 different terminal arrangements depending on application.

EST SYSTEM

The ECM monitors information concerning crankshaft position, engine RPM, engine load, atmospheric conditions, engine temperature, and transmission gear position. The information is used to compute the desired spark timing which is relayed to the distributor enabling appropriate changes to ignition timing.

A back-up spark advance system is also incorporated to signal the ignition module in the event of ECM failure.

HEI (EST) Distributor with Hall Effect Switch External coil model is shown. Scheme 2

Distributors on some 4-cylinder equipped engines contain a Hall Effect switch with shutter blades. The Hall Effect switch and shutter blades act as a second pick-up coil and timer core. When the engine is cranking, the pick-up coil and timer core are used to send RPM impulses to the ECM. When the engine is running, the Hall Effect switch and shutter blades perform this function.

HEI (EST) Distributor with Sealed Module Connector. Scheme 3

HEI (EST) Distributor with Integral Coil. Scheme 4

The distributor module is connected to the ECM by a 4-wire connector and performs the following functions

1. Module terminal "E" triggers the HEI module. The ECM advances or retards spark based on the reference signal from terminal "E". If base timing is incorrectly set, entire advance curve will be incorrect.
2. Module terminal "R" supplies RPM data and crankshaft position reference to the distributor. If wire is open or grounded on fuel injected vehicles, engine will not run.
3. Module terminal "B" is the by-pass circuit. At approximately 400 RPM, ECM applies 5 volts to this circuit which switches spark timing control from HEI module to ECM. On some models, the wire goes through a connector between the 4-wire connector and the ECM. This is disconnected when adjusting base timing. On all models, an open or grounded by-pass circuit will set a Fault Code 42. The engine will run at base timing plus a small amount of advance built into the HEI module.
4. Module terminal "G" is the reference ground. It is grounded to the distributor and ensures there is no voltage drop which could affect performance.
5. On Hall Effect distributors, changes in position of the by- pass switch modifies the circuit between the pick-up coil and ignition coil. RPM signals are supplied to the ECM by the Hall Effect switch. The Hall Effect switch is connected directly to the ECM and not to the distributor module.

Schematic of External Coil HEI (EST) Ignition System. Scheme 5

SENSORS

The coolant temperature sensor advances timing on a cold engine and retards timing as the engine reaches normal operating temperature. If the engine overheats, spark is retarded to prevent detonation. During light throttle operation, the throttle switch allows for additional advance.

Spark advance is also governed by input from engine RPM, and Manifold Absolute Pressure (MAP) sensors. When MAP output voltage is low, the ECM gives more advance. Less spark advance is given when MAP output voltage is high.

On engines with port fuel injection, the ECM will calculate spark advance using information from the Mass Air Flow (MAF) sensor, coolant temperature, and engine RPM. When the engine is under minimum load, based on RPM and low air-flow, increased spark advance is given. When engine is under heavy load based on RPM and high air-flow, less spark advance is given.

Schematic of HEI (EST) Ign Sys with Hall Effect Distributor. Scheme 6

ELECTRONIC SPARK CONTROL SYSTEM (ESC)

The 4 basic components of the Electronic Spark Control (ESC) system are the detonation sensor, HEI (EST) distributor, controller, and the ECM. When detonation (engine knock) occurs, the detonation sensor sends an electrical signal to the ESC. The controller amplifies this signal and transmits it to the ECM. The ECM will retard spark timing until signals from the detonation sensor stop.

Schematic of Electronic Spark Control System. Scheme 7

DIAGNOSTIC SYSTEM

If the reference or EST signals are interrupted due to open circuits or a faulty ECM, the HEI (EST) module will provide a timing signal based on engine RPM, enabling the engine to run, although less efficient.

If the by-pass signal is lost, the by-pass switch will direct flow of information directly to coil rather than through ECM.

Normally, 5-15 seconds after starting a warm engine, the by-pass signal will operate a by-pass switch in the HEI (EST) module. The HEI (EST) module's RPM-controlled timing signal can no longer flow directly to the ignition coil. Instead, it is diverted to the ECM for processing.

Loss of the EST signal when the by-pass signal is on will cause the engine to stop because the HEI (EST) module is no longer sending signals directly to the ignition coil. Any loss of the EST signal will stop all flow to the coil. If vehicle is restarted, the engine will run for a few seconds and then stop when the by-pass signal comes back on.

ADJUSTMENTS

The only adjustments that can be made to the HEI (EST) ignition system are basic ignition timing and spark plug gap.

TROUBLE SHOOTING

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

TESTING

Note. Ignition coils with Red and White leads should be matched with pick-up coils having either a Clear, a Black, or a Blue connector. Ignition coils with Red and Yellow leads must be matched with pick-up coils with a Yellow connector.

Scheme 8

1. Remove coil connector. Using the low scale, connect ohmmeter between coil "BAT" and "TACH" terminals. (Scheme 8) If resistance exceeds 1 ohm, replace ignition coil. (Scheme 8): Testing Ign Coil Resistance (Externally Mounted Coil Shown)
2. Set ohmmeter to high scale. Connect leads between coil "BAT" terminal and a good ground on coil. (Scheme 8) If resistance is less than infinity, replace ignition coil.
3. With ohmmeter still set in high range, connect leads between "TACH" and coil secondary terminal. If resistance is not between 6000-30,000 ohms, replace ignition coil.

Externally Mounted Ignition Coil (Sealed Module Connector Distributor)

Remove coil connectors and secondary coil wire. In test "A", use high scale. (Scheme 9) If continuity is present, replace coil. On test "B", use low scale. Reading should be very low or zero. If not, replace coil. On test "C", use high scale. If there is no continuity, replace coil.

Testing Ignition Coil Resistance Illustration applies to sealed module connector distributors only. Scheme 9

Scheme 10

1. Turn ignition off. Remove the distributor cap and coil assembly. (Scheme 10) Set ohmmeter to low scale. Connect leads to coil "BAT" and "TACH" terminals. If resistance exceeds 1 ohm, replace ignition coil. (Scheme 10): Testing Ign Coil Resistance(Integral Mounted Ign Coil Shown)
2. Set ohmmeter on high scale. Connect one lead to coil secondary terminal and the other lead first to "TACH" terminal and then to ground terminal.
3. If one reading is infinity and other is 6000-30,000 ohms, ignition coil is good. If resistance reading in BOTH instances is infinity, replace ignition coil.

Scheme 11

1. Disconnect pick-up coil leads from HEI (EST) module terminals "N" and "P" (usually Green and White). Set ohmmeter to middle range and connect one lead to either pick-up coil lead and the other lead to distributor housing. Flex pick-up coil leads by hand to check for intermittent shorts. Reading should be infinite at all times. If not, replace pick-up coil. (Scheme 11): Checking Dist Pick-Up Coil (Integral Mounted Ign Coil Shown)
2. Connect ohmmeter between both pick-up coil leads. Check for intermittent opens by flexing wires and connectors. Resistance should read a constant value between 500 and 1500 ohms. If not, replace pick-up coil.

Checking Dist Pick-Up Coil (Extern. Mounted Ign Coil Shown). Scheme 12

Checking Distributor Pick-Up Coil Illustration applies to sealed module connector distributors only. Scheme 13

HALL EFFECT SWITCH TEST

Note. Hall Effect switches cannot be checked with an ohmmeter.

Scheme 14

1. Disconnect 3-wire connector at Hall Effect switch. Connect a 12 volt battery and voltmeter to switch terminals. (Scheme 14) Carefully note polarity markings. (Scheme 14): Testing Hall Effect Switch
2. Insert knife blade straight down between magnet and Hall Effect switch. (Scheme 14) Voltmeter should read within 0.5 volts of battery voltage. With knife blade removed, voltmeter should read between 0 and 0.5 volts. If voltage readings are not as specified, replace Hall Effect switch.

IGNITION SYSTEM CHECK

Note. Before testing, obtain Spark Tester (ST-125). If tachometer is connected to ignition coil "TACH" terminal, disconnect it before performing tests. Use digital voltmeter with 10 megaohms or greater impedance.

1. Remove any spark plug wire and attach Spark Tester (ST-125). Check for spark while cranking engine. If there is no spark, check a second wire in same manner. If there is still no spark, proceed to step 2). If spark occurs, ignition system is not at fault. Check fuel system, and spark plugs.
2. Disconnect 4-wire EST connector between distributor and ECM. Check for spark at tester. If spark is present, replace pick-up coil.
3. If no spark occurred with 4-wire plug disconnected, check voltage at distributor "BATT" terminal while cranking engine.
4. If step 3) reading was less than 7 volts, repair primary circuit back to ignition switch. If 7 volts or more, leave negative lead grounded and check voltage at "TACH" terminal.
5. If step 4) reading was less than 1 volt, ignition coil or ignition coil connector is defective. Repair or replace as necessary. If reading is 10 volts or more, proceed to step 7).
6. If "TACH" terminal voltage was between 1 and 10 volts, replace distributor HEI (EST) module and check for spark. If a spark results, ignition system is functioning. If there is still no spark, replace ignition coil.
7. If "TACH" terminal voltage in step 5) was 10 volts or more, attach Spark Tester (ST-125) to coil output terminal. Crank engine and check for spark. If no spark occurs, proceed to step 9).
8. If spark occurs, check color match of pick-up coil connector and ignition coil lead. Inspect cap for water, cracks or other damage. If no damage is noted, replace rotor. NOTE: Ignition coils with Red and White leads should be matched with pick-up coils having either a Clear, a Black, or Blue connector. Ignition coils with Red and Yellow leads must be matched with pick-up coils with Yellow connector.
9. Remove pick-up coil leads from module. Connect positive lead of voltmeter to coil "TACH" terminal and negative lead to ground. Turn ignition switch to "ON" position. Connect one lead of test lamp to battery positive terminal. Quickly, and for less than 5 seconds, connect other lead to HEI (EST) module terminal "P". Watch voltmeter as test lamp touches terminal.
10. If voltage drops, proceed to step 11). If voltage does not drop, check module ground screw. Also check for open circuits in wires from distributor cap (coil) to distributor. If okay, replace HEI (EST) module.
11. Check for spark with spark tester when test light is removed from module terminal. If spark occurs, the pick-up coil or its connections are defective. Perform Distributor Pick-Up Coil Short and Resistance Check.
12. Ensure ignition coil is properly grounded. Use Distributor Module Tester (J-26792) to check HEI (EST) module. Replace module if defective. Otherwise, replace ignition coil.
13. If no module tester is available, replace ignition coil and repeat steps 7), 9), and 11). If spark results, problem was faulty ignition coil. If no spark results, original ignition coil is probably good. Reinstall original ignition coil and replace HEI (EST) module.

Externally Mounted Ignition Coil

1. Disconnect a spark plug wire and connect spark tester. Check for spark while cranking engine. If no spark is present, check for spark at any other wire. If spark still not present, go to step 2). Intermittent sparking is considered no spark. If spark results, problem is in fuel system or spark plugs.
2. Disconnect 4 terminal EST connector. Check for spark. If spark occurs, replace pick-up coil. If no spark, check for spark at coil wire with Spark Tester (ST-125) while cranking engine. NOTE: Leave Spark Tester (ST-125) connected during remainder of tests.
3. If spark is present while cranking, and distributor cap is free from cracks or other defects replace rotor. If no spark occurred while cranking, remove distributor cap with ignition on and check voltage at HEI (EST) module terminal "+". If measurement is less than 10-volts, repair wire from terminal "+" to ignition coil as well as from primary circuit to ignition switch. If measurement is between 1 and 10-volts, proceed to step 4). If voltage was more than 10 volts, proceed to step 5).
4. Replace HEI (EST) module and check for spark at ignition coil. If spark occurs, system is operating properly. If no spark occurs, replace ignition coil.
5. With ignition switch in "ON" position, check voltage at HEI (EST) module terminal "C". If voltage is less than 1 volt at terminal "C", check for open or grounded lead from ignition coil to terminal "C". If voltage is 10 volts or more, proceed to step 6). Also check ignition coil connections for an open primary circuit.
6. Remove pick-up coil connector from HEI (EST) module. Check voltage at HEI (EST) module terminal "C" with ignition switch in "ON" position. Momentarily connect a test light between battery positive terminal and HEI (EST) module terminal "P" while observing voltmeter.
7. If voltage does not drop, check HEI (EST) module ground. If okay, replace HEI (EST) module. If voltage drops, use a spark tester and check for spark at end of coil wire as test light is removed from module terminal "P". If spark occurs, check pick-up coil and its connections. If spark does not occur, ensure pick-up coil is not grounded then proceed to step 8.
8. Check HEI-EST module with Module Tester (J-26792). Replace module if defective. If module okay, check coil wire from distributor cap to ignition coil. If coil wire okay, replace ignition coil. If no Distributor Module Tester (J-26792) is available, check coil wire from distributor cap. If good, replace ignition coil and repeat step 6).
9. If spark occurs, system is operating properly. If no spark occurs, original coil is good. Reinstall original coil and replace module.

Note. If tachometer is connected to ignition coil "TACH" terminal, disconnect it before performing tests. Use digital voltmeter with 10 megaohms or greater impedance.

Sealed Module Connector Distributor W/ Externally Mounted

Ignition Coil

1. Disconnect a spark plug wire and connect Spark Tester (ST-125). Check for spark while cranking engine. If no spark occurs, check for spark at any other wire. Intermittent sparks are considered no spark. If no spark occurs, proceed to step 2). If spark occurs, the problem is in fuel system or spark plugs.
2. Unplug 4-terminal EST connector. Check for spark at tester. If spark occurs, replace pick-up coil. If no spark occurs, check for spark at coil wire with Spark Tester (ST-125) while cranking engine. NOTE: Leave Spark Tester (ST-125) connected during remainder of tests.
3. If spark is present while cranking, inspect cap for cracks or other defects. If okay, replace rotor. If no spark while cranking, disconnect distributor 2-wire "C/+" (coil) connector. Turn ignition on and check voltage at "+" and "C" terminals of harness connector.
4. If less than 10 volts at terminal "C" only, check for open or ground in circuit from "C" to ignition coil. If both terminals read less than 10 volts, proceed to step 5). If both terminals read 10 volts or more, proceed to step 6). If circuit is good, fault is ignition coil or connections.
5. Repair wire from module "+" terminal to "B" terminal of Black ignition coil connector or primary circuit to ignition switch.
6. Check voltage from "TACH" lead to ground with ignition on. Reconnect distributor 2-wire connector.
7. If voltage less than 1 volt in step 6), repair open tachometer lead or connector and repeat step 6). If voltage reading is 1-10 volts in step 6), replace module and check for spark as described in step 1). If spark present, system is good. If no spark, replace ignition coil.
8. If voltage is more than 10 volts in step 6), connect test light from "TACH" lead to ground. Crank engine and observe light. If light blinks, replace ignition coil and recheck for spark with Spark Tester (ST-125). If still no spark, install original coil and replace module.
9. If light remains steady in step 8), unplug distributor 4-wire connector. With ignition on, remove distributor cap and retaining screw in 4-wire end of module.
10. Loosen remaining module screw and pivot module out to gain access to pick-up coil terminals. Connect jumper from module retaining screw eyelet to ground. Disconnect pick-up coil from module. Connect voltmeter between "TACH" terminal and ground. Insulate test light probe to 1/4" from tip. Note voltage as test light is momentarily connected between module terminal "P" and 12 volt source. DO NOT allow test lamp to be connected for more than 5 seconds.
11. If no voltage drop, ensure module is properly grounded. If good ground is noted, replace module. If voltage drops, check for spark at coil wire with Spark Tester (ST-125) when test light is removed from module terminal.
12. If spark is present in step 11), check pick-up coil resistance or connections. If no spark in step 11), check module with Module Tester (J-26792). Replace module if defective. Otherwise, check coil wire between cap and coil. If wire good, replace coil.
13. If Module Tester (J-26792) was not available in step 12), replace ignition coil and repeat step 9). If spark is now present, system is good. If no spark present, original ignition coil was good. Reinstall original coil and check coil wire. If coil wire good, replace module.

INTERMITTENT OPERATION CHECK

1. Connect Spark Tester (ST-125) to 2 different spark plug wires. If no spark, go to Ignition System Check. If spark is present on either or both wires, check for dwell increase from low to high RPM.
2. Check pick-up coil and Hall Effect switch (if equipped). Replace if faulty. If pick-up coil and Hall Effect switch are good, and dwell did not increase, replace HEI (EST) module. If pick-up coil and Hall Effect switch are good, and dwell increased, check fuel system, spark plug wires, distributor cap, and spark plugs.

Scheme 15

1. With selector lever in "P" (auto. trans.) or Neutral (man. trans.), run engine at fast idle. Note timing change as "TEST" terminal is grounded. (Scheme 15) If timing changes, system is operating properly. (Scheme 15): Test Terminal Location Timing should change when test terminal is grounded. CAUTION: Prior to placing automatic transmission in "D" position in following step, ensure emergency brake is FIRMLY applied and wheels are securely blocked.
2. If timing does not change on vehicles with manual transmissions, go to step 3). If timing does not change on vehicles with automatic transmissions, let engine return to idle. Place selector lever in "D" and note timing change as test terminal is grounded. If timing changes, system is operating properly.
3. If no change in timing occurs, check voltage at output of MAP sensor or vacuum sensor as vacuum hose is removed and reinstalled. If no change occurs, problem is in the vacuum or MAP sensor circuit. If voltage output changes, proceed to step 4).
4. Disconnect park/neutral switch and recheck for timing change. If timing changes, problem is either an improperly adjusted or faulty park/neutral switch. If timing does not change, check for grounded wire from terminal "H" of ECM to park/neutral switch. If wire is not grounded, replace ECM.

Fuel Injected Engines

1. The ECM will set timing at a specified value when the "TEST" terminal is grounded.
2. Note timing when terminal is not grounded. Ground "TEST" terminal and check for timing change at 2000 RPM. If timing changes, the EST is operating properly.

ESC PERFORMANCE CHECK

Note. Perform these checks only after checking ignition timing, MAP, EGR operation or if engine overheats.

1. Connect tachometer to engine. Place shift lever in "P" (auto. trans.) or NEUTRAL (man. trans.). Run engine at fast idle (about 1500 RPM). With engine at normal operating temperature, tap engine block in area of detonation sensor. If RPM drops, system is operating properly.
2. If RPM did not drop, disconnect ESC controller (located in engine compartment) and check for RPM change. If no change in RPM, proceed to step 5). If RPM drops, run engine at 2000 RPM. Unplug controller harness. Connect a digital voltmeter between ESC harness connector terminals "E" and "D". Voltage should not exceed 0.08 volts on the AC scale.
3. If voltage reading is correct, problem is a faulty ESC connection or ESC controller. If voltage is not correct, check for an open in wire from ESC controller connector terminal "D" to ground.
4. Repair if an open is found. If no open is found, check for an open or a poor connection between detonation sensor and ESC controller connector terminal "E". If circuit is okay, replace the detonation sensor.
5. Inspect "CHECK ENGINE" light. If light is on, problem is most likely a faulty ESC controller or detonation sensor. If light is off, turn ignition switch to "ON" position (engine not running) and check voltage from ground to ESC terminal "C".
6. If voltage is under 2 volts, replace ECM. If voltage is over 2 volts, repair short in wire from ESC terminal "C" to ECM terminal "L".

Note. A Knock Sensor to controller wire that is routed too close to spark plug wires may cause retarded timing due to a false signal.

DISASSEMBLY

1. On distributors with integral ignition coils, detach 4-wire EST connector and wiring connector from cap. Turn 4 latches and remove cap and coil assembly from lower housing. To remove coil, remove coil cover attaching screws, cover, and coil attaching screws. Lift coil with leads from cap.
2. Remove rotor. Remove coil arc seal and clean cap with soft cloth, checking for cracks or other damage.
3. On vehicles with external coils, remove coil connector and disconnect 4-wire EST connector and 2-wire coil connector. Turn 2 latches and lift off distributor cap. Remove rotor.
4. On all models, disconnect pick-up coil leads from HEI (EST) module. Remove Hall Effect switch (if equipped) by removing 2 attaching screws. Mark distributor shaft and gear for reassembly. Drive out roll pin and remove distributor shaft.
5. On models with integral coil, remove magnetic shield. On all models, remove "C" washer, pick-up coil, magnet, and pole piece. Remove 2 module attaching screws and capacitor screw (if equipped). Lift module, capacitor, and harness assembly from distributor housing. Disconnect wiring harness from module.

REASSEMBLY

Reassemble in reverse order of disassembly procedure. Wipe distributor housing and module clean and apply silicone grease between module and housing. Spin shaft to ensure timer core external teeth do not strike pole piece internal teeth.

See also:
• TROUBLE SHOOTING - BASIC PROCEDURES