Ignition System - 4-cyl Chevrolet Camaro II

DESCRIPTION

The Delco-Remy HEI-EST system, a part of all General Motors Computer Command Control systems, is designed to provide optimum performance through electronic control of air/fuel ratios, spark timing, air management and idle speed.

The distributor has neither vacuum nor centrifugal advance mechanisms. (Scheme 1)and (Scheme 2). The distributor contains a 7-terminal HEI-EST control module, a timer core, pick-up coil, radio noise suppression capacitor, and on most models, an integrally mounted ignition coil, located under the distributor cap's coil cover. Distributors on vehicles equipped with 2.5L VIN 2 and 2.5L VIN R engines also contain a Hall Effect switch and shutter blades.

Disassembled View of HEI-EST Distributor Integral coil model shown. Scheme 1

HEI-EST Distributor with Hall Effect Switch External coil model shown. Scheme 2

The Hall Effect switch and shutter blades act as a second pick-up coil and timer core. When the engine is in the cranking mode, the pick-up coil and timer core are used to send RPM impulses to the ECM. When the engine is in the run mode, the Hall Effect switch and shutter blades perform this function.

On 2.5L VIN 2 and 2.5L VIN R engines, the shutter blades point upward since the ignition coil is mounted externally (not in the distributor cap). The number of shutter blades must equal the number of cylinders in the engine being used.

The distributor is connected to the EST system by means of a 4-wire connector, leading to the external electronic control module (ECM). The ECM (not the distributor HEI-EST module) receives voltage signals from a number of sensors. A typical system could be provided signals from oxygen, engine coolant temperature, throttle position, barometric pressure and manifold absolute pressure sensors, as well as the distributor pick-up coil and Hall Effect switch (if equipped).

Schematic of HEI-EST Ignition System Including Relationship to Computer Command Control Electronic Control Module. Scheme 3

There are 4 basic components to the ESC system. They include detonation sensor, an HEI-EST distributor, an ESC controller, and the ECM. When detonation (engine knock) occurs, the detonation sensor sends an electrical signal to the ESC controller. The ESC controller amplifies this signal and transmits it to the ECM. ECM then retards the spark timing until it no longer receives a signal from the detonation sensor, through the ESC controller.

Schematic of Electronic Spark Control System. Scheme 4

OPERATION

During cranking or in event of EST ECM failure, a by-pass signal from ECM terminal 11 to the HEI-EST module terminal "B" is either absent or low. (Scheme 3) This notifies the HEI-EST module to take over control of spark advance and to ignore any EST information coming from the ECM. During this period, poor engine performance may result under some conditions, but the diagnostic "CHECK ENGINE" light will not come on.

The HEI-EST module will then convert pick-up coil RPM signals and transmit them through the by-pass switch and terminal "C" directly to the negative "TACH" terminal of the ignition coil. These signals turn the coil primary circuit on and off, causing a surge in the secondary that fires the spark plugs.

When engine speed reaches 600 RPM or more (about 5-15 seconds after starting), the ECM transmits a constant 5-volt signal to the distributor HEI-EST module, changing the position of the by-pass switch. This has the following effect

Scheme 5

1. On models equipped with a regular distributor (without a Hall Effect switch), the pick-up coil's RPM signals can no longer flow directly to the ignition coil as this circuit is now open. Instead the signals are converted in the distributor module and routed through terminal "R" to ECM terminal 10. (Scheme 5): HEI-EST Ignition System with Hall Effect Distributor
2. On models equipped with a distributor having a Hall Effect switch, the change in position of the by-pass switch opens the circuit between the pick-up coil and ignition coil. The pick-up coil has no RPM reference connection to the ECM, as HEI-EST module terminal "R" is not used. The function of supplying RPM signals to the ECM is then accomplished by the Hall Effect switch. The wires from the Hall Effect switch connect directly to the ECM and do not connect to the distributor module.

The PROM (Programmed Read Only Memory) portion of the ECM carries the basic spark advance curve based on engine RPM. Spark Timing is calculated by the ECM whenever an ignition pulse is present. However, spark advance information is only sent to the distributor when the engine is running (not during cranking). Engine sensor values are used by the ECM to modify the PROM information, increasing or decreasing spark advance to achieve maximum performance with minimum emissions.

The coolant temperature sensor advances spark on a cold engine and reduces advance as the engine reaches normal operating temperature. If the engine is too hot, spark is retarded to prevent detonation.

During light throttle operation, the throttle switch allows for additional advance. Additional adjustment results from input from coolant temperature, engine RPM and manifold absolute pressure (MAP) sensors. When MAP is low, spark is at maximum advance.

As load increases and pressure increases, spark timing is retarded to allow the engine to maintain its proper performance and emission level.

After computation of all information from the various sensors, a compensated ignition spark timing signal is sent through the HEI-EST module's terminal "E", the by-pass switch, and terminal "C", to the ignition coil negative terminal. Each time the signal is flashed on and off, the coil's primary circuit is turned on and off. As this occurs, a voltage surge occurs in the secondary that fires the spark plugs.

The ECM is continually computing sensor information to maintain efficient engine performance with low emission levels, doing so under varying engine conditions.

Note. The shape of the HEI-EST module used on 4-cylinder engines differs from those of other HEI-EST modules. However, it also has 7 terminals and operates in the same manner.

ADJUSTMENTS

The only adjustments that can be made to HEI-EST ignition system are basic ignition timing and spark plug gap. No other adjustments are necessary.

TROUBLE SHOOTING

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

PRE-TESTING DIAGNOSIS

If the reference or EST signals are interrupted due to open wires or a faulty ECM, the vehicle will still run. The HEI-EST module will provide a timing signal based on engine RPM.

If the by-pass signal is lost, the ECM cannot control spark timing, as the by-pass switch will permit direct flow of information to the ignition coil rather than to the ECM.

Normally, a few seconds (5-15 seconds) after starting a warm engine, the by-pass signal electronically operates 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, but is diverted first to the ECM for modification by information received from the engine sensors.

Loss of the EST signal with the by-pass signal "ON", however, will stop the engine, because the HEI-EST module is no longer sending signals directly to the ignition coil, but to the ECM, and any loss of the EST signal cuts all flow to the coil. If an attempt is made to restart the vehicle, the engine will run for a few seconds and then stop when the by-pass signal comes back on.

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 6

1. Remove coil connector. Using the low scale, connect ohmmeter leads to coil's battery and "TACH" terminals. (Scheme 6) Resistance should be 0-1 ohm. If not, replace ignition coil. (Scheme 6): Ignition Coil Resistance Test Points Externally mounted ignition coil.
2. Set ohmmeter to high scale and connect leads to battery terminal and a good ground on coil. (Scheme 6) Resistance reading should be infinity. If not, replace ignition coil.
3. With ohmmeter still set in high range, connect leads to "TACH" terminal and to secondary terminal. (Scheme 6) Resistance should be 6,000-30,000 ohms. If not, replace ignition coil.

Scheme 7

1. Disconnect pick-up coil leads from HEI-EST module terminals "N" and "P" (usually a Green and a White wire). To check for shorted pick-up coil, set ohmmeter in middle range.
2. Connect one lead to either pick-up coil lead and other lead to distributor housing. Flex pick-up coil leads by hand to check for intermittent shorts. (Scheme 8)and (Scheme 9). Reading should be infinite at all times. If not, replace pick-up coil. (Scheme 7): Distributor Pick-Up Coil Short & Resistance Checks Integral mounted ignition coil.
3. Connect ohmmeter leads to both pick-up coil leads. (Scheme 8)and (Scheme 9). Flex wires and connectors to locate intermittent opens. Resistance should read a constant unchanging value between 500 and 1500 ohms. If not, replace pick-up coil.

Distributor Pick-Up Coil Short & Resistance Checks Externally mounted ignition coil. Scheme 8

HALL EFFECT SWITCH TEST

Note. Hall Effect switches cannot be checked with an ohmmeter like a pick-up coil.

Scheme 9

1. Disconnect 3-wire connector at Hall Effect switch. Connect a 12-volt battery and voltmeter to switch terminals. (Scheme 9) Carefully note polarity markings. (Scheme 9): Testing Hall Effect Switch
2. Insert knife blade straight down between magnet and Hall Effect switch. (Scheme 9) 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 described, replace Hall Effect switch.

IGNITION SYSTEM CHECK

Note. Before making the following tests, obtain a spark tester. If tachometer is connected to ignition coil "TACH" terminal, disconnect it before performing tests. Use a digital voltmeter with 10 megohms impedance or larger.

Integrally Mounted Ignition Coil

1. Remove a spark plug wire and attach spark tester to wire. Crank engine and check for spark at tester gap. If there is no spark, check a second wire in same manner. If sparks result, ignition system is not at fault. Suspect fuel system or spark plugs.
2. If no spark resulted in step 1, disconnect 4-wire EST connector between distributor and ECM. Crank engine and recheck for spark at tester gap. If spark occurs with EST connector disconnected, proceed to EST System Check.
3. If no spark occurred in step 2, with 4-wire connector disconnected, check voltage at battery terminal of ignition coil. Attach positive voltmeter lead to battery terminal of ignition coil and negative lead to ground. Check for voltage while cranking engine.
4. If reading is less than 7-volts, repair primary circuit back to ignition switch. If 7-volts or more, move positive voltmeter lead from battery terminal to "TACH" terminal. Leave negative lead grounded.
5. If reading is under 1 volt, ignition coil connection or ignition coil is defective. Repair or replace as necessary. If 10 volts or more is registered on voltmeter, proceed to step 7. If voltmeter reading is 1-10 volts, proceed to step 6.
6. If voltage reading on "TACH" terminal was 1-10 volts, replace distributor HEI-EST module and check for spark, following procedure outlined in steps 7, 9, and 11. However, if a spark results in step 11, ignition system is okay following module replacement. If there is still no spark, replace ignition coil also, as it too is defective.
7. If in step 5, 10 volts or more were read on "TACH" terminal, attach spark tester to coil output terminal (inside distributor cap) with cap still connected to distributor by wiring harness. Crank engine and check for spark.
8. If no spark occurs, proceed to step 9. If spark occurs, check color match of pick-up coil connector and ignition coil lead (see note). Inspect cap for water, cracks or other damage. If okay, replace rotor. 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.
9. If no spark occurred in step 7, remove pick-up coil leads from module. Connect positive lead of voltmeter to coil "TACH" terminal and negative lead to ground. Turn ignition on. For no more than 5 seconds, connect test lamp from battery positive supply 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 in wires from distributor cap (coil) to distributor. If okay, replace HEI-EST module.
11. If voltage dropped in step 10, check for spark at tester gap (still attached to coil output terminal) when test light is removed from module terminal. If spark occurred, either pick-up coil or its connections are defective. Perform Distributor Pick-Up Coil Short and Resistance Check if not done previously. Resistance should be 500-1500 ohms.
12. If distributor module tester is available, check HEI-EST module. If okay, check ignition coil ground. If ground is okay, replace ignition coil. If module is defective, replace.
13. If no module tester is available, check ignition coil ground circuit. If okay, replace ignition coil and repeat steps 7, 9, and 11. If spark results, system is okay. If no spark results, original ignition coil is okay. Reinstall original ignition coil and replace HEI-EST module.

Externally Mounted Ignition Coil

1. Remove a spark plug wire and connect a spark tester to it. Check for spark while cranking engine. If no spark results, check for spark at another wire. If spark results, problem is in fuel system or spark plugs. If no spark occurs, proceed to step 2.
2. If no spark occurred in step 1, remove the secondary ignition coil wire from the distributor cap. Connect spark tester to end of wire. Check for spark while cranking engine. If no spark occurs, proceed to step 3. If spark occurs, check distributor cap for water or cracks. If okay, replace rotor.
3. Remove distributor cap but leave it connected to distributor with wiring harness. Connect negative voltmeter lead to ground and positive lead to HEI-EST module terminal "+". Turn ignition on. If voltage is 10 volts or more, proceed to step 4. If voltage is less than 10 volts, repair wire from terminal "+" to ignition coil and primary circuit to ignition switch.
4. If voltage was 10 volts or more in step 3, leave ignition on and negative voltmeter lead grounded. Connect positive lead to HEI-EST module terminal "C". If voltage is under 1 volt, check for open or grounded lead from ignition coil to terminal "C", ignition coil connections or for an open primary circuit in ignition coil.
5. If voltage was 10 volts or more, proceed to step 6. If voltage was 1-10 volts, replace HEI-EST module and check for spark from ignition coil as described in step 7. If sparks occur, system is operating properly. If no sparks occur, replace ignition coil as it too is defective.
6. If voltage was 10 volts or more in step 4, remove pick-up coil connector from HEI-EST module. Connect negative voltmeter lead to ground and positive lead to HEI-EST module terminal "C". Turn ignition on. Momentarily connect a test light between battery voltage 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 does drop, use a spark tester and check for spark at end of coil wire as test light is removed from HEI-EST module terminal "P". If spark does not occur, proceed to step 8). If spark does occur, check pick-up coil and its connections. Also make sure pick-up coil is not grounded.
8. If distributor module tester is available, check HEI-EST module. If okay, check secondary wire from distributor cap to ignition coil. If okay, replace ignition coil. If module is defective, replace. If no distributor module tester is available, replace the HEI-EST module and repeat step 7.
9. If spark occurs, system is operating properly. If no spark occurs, HEI-EST module removed is okay. Reinstall original module and check secondary wire from distributor cap to ignition coil. If okay, replace ignition coil.

INTERMITTENT OPERATION CHECK

1. Connect spark tester to 2 different spark plug wires. If no spark, perform Ignition System Check. If spark 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). If faulty, replace. If pick-up coil and Hall Effect switch are good and dwell did not increase, replace HEI-EST module. If good, but dwell did increase, check fuel system, spark plug wires, distributor cap and spark plugs.

EST EMISSION SYSTEM CHECK

1. With shift lever in "P" (auto. trans.) or Neutral (man. trans.), run engine at fast idle and note timing change as test terminal is grounded. If timing changes, system is operating properly.
2. If timing does not change on vehicles equipped with manual transmissions, proceed to step 3. If timing does not change on vehicles equipped with automatic transmissions, let engine return to idle and place transmission in "D". Note timing change as test terminal is grounded. If timing changes, system is operating properly.
3. On all models, if there are no change in timing, check voltage at output of MAP (Manifold Absolute Pressure) 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.

Scheme 10

1. With engine at fast idle, check timing. Ground test terminal and note if timing changes. If timing does change, system is operating properly. If timing does not change, stop engine and disconnect 4-wire EST connector from distributor.
2. Connect a jumper wire from terminal "A" to "B" on distributor side of EST connector. (Scheme 10) Start engine, ground test terminal and connect test light from battery positive terminal to terminal "C" of EST connector. (Scheme 10): Test Light Hook-Up for Checking EST Emission System
3. If engine stops, check for open wire from EST terminal "E" to ECM. If wire is okay, replace either HEI-EST connector or module. If engine runs, remove jumper wire from terminals "A" and "B" while leaving test light connected. If engine runs, proceed to step 4. If engine stops, proceed to step 5.
4. If engine continued to run in step 3), check distributor wires for open or ground to HEI-EST module terminal "B" or short between module terminals "R" and "E". If wires are okay, repair faulty HEI-EST module connection or replace HEI-EST module.
5. If engine stopped in step 3), check for open wire from EST connector terminal "A" to ECM connector terminal "12". Also check for open or grounded wire from EST connector terminal "C" to ECM connector terminal "11". If wires are okay, replace faulty ECM connector or ECM.

Note. ECM connector terminal numbers may vary between models.

ESC PERFORMANCE CHECK

Note. Perform these checks only after checking other causes of engine detonation, such as ignition timing, MAP, lack of EGR, or engine temperature.

1. Connect tachometer to engine and run at fast idle speed (about 1500 RPM). Place shift lever in "P" (auto. trans.) or Neutral (man. trans.). With engine at normal operating temperature, tap engine block in area of detonation sensor. If engine RPM drops, system is operating properly.
2. If RPM did not drop, disconnect ESC controller and check for RPM change. If no change in RPM, proceed to step 5. If RPM drops, run engine at 2000 RPM. Connect a digital voltmeter between ESC harness connector terminals "E" and "D". On the A.C. scale, reading should not be higher than .08-volts.
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. If there was no change in RPM in step 2, note "CHECK ENGINE" light. If light is on, problem is most likely a faulty ESC controller, but also check detonation sensor. If light is off, turn ignition on (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".

OVERHAUL

Note. When distributor is removed from l.6L engine, the fuel pump rod MUST be removed first.

DISASSEMBLY

1. On distributors with integral ignition coils, detach 4-wire EST connector and wiring connector from cap and turn 4 latches. 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 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. Turn 2 latches and lift off distributor cap.
4. On all models, remove rotor and disconnect pick-up coil leads from HEI-EST module. (Scheme 1) Remove Hall Effect switch (if equipped) by removing 2 attaching screws. Mark distributor shaft and gear shaft.
5. On models with integral coil, remove magnetic shield. Then remove retaining "C" washer, pick-up coil, magnet and pole piece. Remove 2 module attaching screws and capacitor screw. Lift module, capacitor and harness assembly from distributor housing. Disconnect wiring harness from module.

REASSEMBLY

Assemble in reverse order. Make sure to wipe distributor housing and module clean and apply silicone grease between module and housing. Spin shaft to be sure timer core external teeth do not strike pole piece internal teeth.

See also:
• TROUBLE SHOOTING - BASIC PROCEDURES