Ignition System - Hei-Est Cadillac Brougham I

DESCRIPTION

The Delco-Remy High Energy Ignition Electronic Spark Timing (HEI-EST) system consists of distributor housing, rotor, cap, 7 or 8-terminal ignition module, magnetic pick-up, pole piece, pick-up coil, connecting harness and the EST portion of the ECM. On some models, the ignition coil is contained within the distributor cap, while others have an externally mounted coil. (Scheme 1)and (Scheme 2). A capacitor is installed in the distributor for radio noise suppression.

No vacuum or centrifugal advance mechanisms are used. All spark timing changes are controlled by the Electronic Control Module (ECM) based upon monitored input signals. Some models use an additional Electronic Spark Control (ESC) ignition retard system in the event of engine detonation (knock). Most models are equipped with sealed ignition coil and ignition module connectors. (Scheme 2)

Scheme 1

When the external teeth on the timing core approach, align with, and pass the internal teeth on pole piece, an alternating current is induced in the pick-up coil windings. In the cranking mode, this alternating current signals switching transistors in the HEI module to make or break the ignition coil primary ground circuit. Once engine has started ECM takes control of primary ground circuit (EST mode).

When the primary ground circuit is removed, the magnetic field created by the flow of current in the primary windings collapses across the primary and secondary windings of the coil. This induces a high-voltage surge in the secondary windings of the coil. Secondary voltage is then discharged to the rotor which distributes it to the appropriate spark plug terminal. The distributor module may have either a 7-terminal ignition module, or an 8-terminal ignition module (sealed connector module), depending on application.

Scheme 2

EST SYSTEM

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

The distributor module is connected to ECM by a 4-wire EST connector. Wires perform the following functions

Reference (RPM) Wire

Alternating current signals from the pick-up coil are converted by the ignition module converter to digital signals for used by the ECM. This supplies RPM data and crankshaft position reference to the ECM. Since the signal on this wire is used as an injector trigger reference on fuel injected vehicles, if wire is open or grounded, engine will not run.

By-Pass Wire

When an engine speed signal of approximately 400 RPM is received by the ECM, ECM considers engine to be running and applies 5 volts to the ignition module on the by-pass wire. This causes ignition module to switch timing control over to the variable timing control circuit in the ECM. On some models, this by-pass wire contains a connector located 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 Code 42 in ECM memory. The engine will run at base timing plus a small amount of advance built into the HEI module.

EST Wire

When 5 volts is present on the by-pass wire and ignition module has turned control of engine timing over to ECM, the ECM advances or retards spark on this wire based on calculations involving the reference signal and other sensor input signals. (Scheme 3) If base timing is incorrectly set, entire advance curve will be incorrect.

Ground Wire

This is the reference ground. It is grounded at distributor and ECM, ensuring there is no voltage drop in the EST circuit which could affect ignition operation.

Scheme 3

SENSORS

The coolant temperature sensor signals ECM to advance timing on a cold engine and return timing to programmed advance curve as engine reaches normal operating temperature. If engine overheats, spark is retarded to prevent detonation. During light throttle operation, throttle position sensor input to ECM allows for additional advance.

Spark advance is also governed by input from engine RPM and Manifold Absolute Pressure (MAP) sensor. When MAP output voltage is low (high vacuum), ECM provides more spark advance. Less spark advance is given when MAP output voltage is high (low vacuum), helping to reduce the possibility of engine detonation.

On engines not equipped with MAP sensors, ECM will calculate spark advance using information from Mass Airflow (MAF) sensor, coolant temperature sensor and engine RPM. When engine is under minimum load, based on low RPM and low mass airflow signals, more spark advance is given. When engine is under heavy load based on high RPM and high mass airflow signals, less spark advance is given to eliminate possible detonation.

ELECTRONIC SPARK CONTROL (ESC) SYSTEM

The basic components of Electronic Spark Control (ESC) system are detonation (knock) sensor, HEI/EST distributor, ESC controller (on some models), and the ECM. On some fuel injected models, the function of the ESC controller is built into the Memory Calibration (MEM-CAL) unit of the ECM.

On controller-equipped systems, when detonation (knock) occurs, sensor sends an electrical signal to controller. Controller will then remove the 12-volt signal from the ECM-monitored knock signal wire. When the ECM senses a voltage drop (to less than one volt) on the knock sensor signal line, spark timing will be retarded. The ECM will gradually retard spark timing until the 12-volt signal from the ESC controller returns. If signal wire were to become open or grounded, ECM would continuously provide full ignition timing retard.

On vehicles using ECMs containing MEM-CAL units, the ECM supplies and monitors a 5-volt DC reference signal on the knock sensor signal line. Internal circuitry of the knock sensor will pull this voltage down to about 2.5 volts. When knock occurs, the knock sensor produces an AC voltage signal which rides on the 2.5-volt DC signal. The voltage and frequency of this signal depend upon knock signals received by the sensor. The ECM will retard spark timing until signals from detonation sensor cease.

Scheme 4

ADJUSTMENTS

The only adjustments that can be made to 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.

DIAGNOSIS

If EST circuitry inside the ECM should fail, internal back-up circuitry will provide a timing signal based solely on engine RPM. Engine will continue to run, although less efficiently. If RPM reference to ECM or by-pass signal to ignition module is lost, by-pass switch will direct pick-up coil RPM information directly to ignition coil rather than to ECM. This will cause fuel injected vehicles to stall. Carbureted vehicles may continue to run, however, performance will be reduced due to the limited advance built into the ignition module.

Loss of EST signal from ECM when 5-volt by-pass signal is present will cause engine to stop because ignition module is no longer sending signals directly to ignition coil. Any loss of EST signal will stop all flow to coil. If vehicle is restarted, engine will run for a few seconds and stop when by-pass signal comes back on.

Loss of HEI reference ground wire may cause ECM to monitor an incorrect engine speed signal. This could result in multiple firings of fuel injectors, incorrect RPM readings on a "Scan" tester, ignition cut-out or setting of a false Code 42.

Externally Mounted Ignition Coil

Remove coil connectors and secondary coil wire. In test "A", use high ohmmeter scale. (Scheme 5) Resistance value should be very high (infinite). If not, replace coil. In test "B", use low ohmmeter scale. Reading should be very low or near zero volts. If not, replace coil. In test "C", use high ohmmeter scale. If there is no continuity, replace coil.

Scheme 5

Integrally Mounted Ignition Coil

1. Turn ignition off. Remove the distributor cap and coil assembly. Turn cap upside down. (Scheme 6) Set ohmmeter to low scale. Connect leads to coil "BAT" and "TACH" terminals. If resistance exceeds zero, or nearly zero, replace ignition coil.
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. If resistance reading in BOTH instances is infinite, replace ignition coil.

Scheme 6

DISTRIBUTOR PICK-UP COIL SHORT & RESISTANCE CHECKS

1. Disconnect pick-up coil leads from HEI/EST module terminals "N" and "P". Set ohmmeter to middle scale 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 to ground. Reading should be infinity at all times. If not, replace pick-up coil.
2. Connect ohmmeter between both pick-up coil leads. Check for intermittent opens by flexing wires and connectors. Resistance should be 500-1500 ohms. If not, replace pick-up coil.

Scheme 7

IGNITION SYSTEM CHECK

Note. For ignition system testing procedures, see appropriate CHART C-4 in THE appropriate TESTS W/CODES article in the ENGINE PERFORMANCE section. See following list. If "engine cranks, but will not run", proceed to appropriate CHART A-3 for fuel injected vehicles. Proceed to appropriate "symptom" in appropriate THEORY & OPERATION article in the ENGINE PERFORMANCE section for carbureted vehicles.

1. For 2.0L VIN [K], see: «2.0L(K)/2.5L TESTS W/CODES»(ref-94904)
2. For 2.0L VIN [1], see: «2.0L VIN [1] TESTS W/CODES»(ref-94905)
3. For 2.0L Turbo, see: «2.0L TURBO TESTS W/CODES»(ref-94910)
4. For 2.5L, see: «2.0L(K)/2.5L TESTS W/CODES»(ref-94904)
5. For Camaro & Firebird 2.8L: «2.8L VIN [S] PFI TESTS W/CODES»(ref-94911)
6. For 3.1L, see: «3.1L VIN [T] PFI TESTS W/CODES»(ref-58099)
7. For 3.3L, see: «3.3L/3.8L PFI TESTS W/CODES»(ref-58100)
8. For 3.8L, see: «3.3L/3.8L PFI TESTS W/CODES»(ref-58100)
9. For 4.3L, see: «4.3L TBI TESTS W/CODES»(ref-94912)
10. For 5.0L PFI, see: «5.0L/5.7L PFI TESTS W/CODES»(ref-94913)
11. For 5.7L PFI, see: «5.0L/5.7L PFI TESTS W/CODES»(ref-94913)
12. For Cadillac Brougham, see: «CCC V8 CARBURETOR TESTS W/CODES»(/cadillac/brougham/i-1987-1992/remont/testing-diagnostics/#ccc-v8-carburetor-tests-wcodes)
13. For All other Cadillac with DFI, see: «DFI TESTS W/CODES»(ref-58101)

Preliminary Testing Procedures

Before testing, obtain Spark Tester (ST-125). (Scheme 8)and (Scheme 9). If factory tachometer is connected to ignition coil tachometer terminal, disconnect it before performing tests. When performing tests, use digital voltmeter with at least 10-megohm input impedance. When removing spark plug wire from spark plug, twist and pull on boot, NOT on wire.

Scheme 8

Scheme 9

INTERMITTENT OPERATION CHECK

1. Check fuel system, spark plug wires, distributor cap, and spark plugs. Most intermittent problems are caused by faulty electrical connections. Visually inspect wiring for a fault. Drive vehicle with a voltmeter connected to a suspected circuit.
2. Using a "Scan" tester, monitor input signals. See SCAN TESTER USAGE and SCAN DATA tables in appropriate THEORY & OPERATION article in the ENGINE PERFORMANCE section. Check for electrical system interference caused by a defective relay, ECM driven solenoid or switch causing a sharp electrical surge. Problem should occur when faulty component is operated. If problem ceases when component is disconnected, component is at fault.
3. Check for proper HEI distributor ground circuit. Check for improper installation of electrical options such as lights, radios, etc. Check for open diode(s) across A/C compressor clutch and other possible defective diodes.

Carbureted Engines

1. With transmission in Park of Neutral, run engine at fast idle. Note timing change as the ALDL "test" terminal is grounded. (Scheme 10) If timing changes, system is operating properly. CAUTION: Prior to placing automatic transmission in Drive in following step, ensure emergency brake is FIRMLY applied and DRIVE 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 transmission in Drive 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. On vehicles with automatic transmission, 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 Park/Neutral signal wire between ECM and Park/Neutral switch. If wire is not grounded, replace ECM. Prior to replacement of ECM, see ECM REPLACEMENT in the appropriate THEORY & OPERATION article in the ENGINE PERFORMANCE section.

Fuel Injected Engines

The ECM will set timing at a specified value when the ALDL "test" terminal is grounded. (Scheme 10) Note timing when terminal is not grounded. Increase engine speed to 2000 RPM. Ground "test" terminal and check for timing change. If timing changes, the EST is operating properly.

Scheme 10

Note. For information on specific ALDL connector locations, see appropriate component location chart in GM CCC article in the appropriate TESTS W/CODES article in the ENGINE PERFORMANCE section. See list at end of article.

ESC PERFORMANCE CHECK

For testing of ESC system, see appropriate General Motors component CHART C-5 in the appropriate TESTS W/CODES article in the ENGINE PERFORMANCE section. See following list. Perform this test for complaints of poor performance/fuel economy or detonation (knock). Perform checks only after checking ignition timing, MAP and EGR operation or if engine overheats. Also, perform appropriate DIAGNOSTIC CIRCUIT CHECK in the appropriate TESTS W/CODES article in the ENGINE PERFORMANCE section. See the following list. If Code 43 is present, proceed to appropriate chart for that code prior to performing the CHART C-5 checks.

1. For 2.0L VIN [K], see: «2.0L(K)/2.5L TESTS W/CODES»(ref-94904)
2. For 2.0L VIN [1], see: «2.0L VIN [1] TESTS W/CODES»(ref-94905)
3. For 2.0L Turbo, see: «2.0L TURBO TESTS W/CODES»(ref-94910)
4. For 2.5L, see: «2.0L(K)/2.5L TESTS W/CODES»(ref-94904)
5. For Camaro & Firebird 2.8L: «2.8L VIN [S] PFI TESTS W/CODES»(ref-94911)
6. For 3.1L, see: «3.1L VIN [T] PFI TESTS W/CODES»(ref-58099)
7. For 3.3L, see: «3.3L/3.8L PFI TESTS W/CODES»(ref-58100)
8. For 3.8L, see: «3.3L/3.8L PFI TESTS W/CODES»(ref-58100)
9. For 4.3L, see: «4.3L TBI TESTS W/CODES»(ref-94912)
10. For 5.0L PFI, see: «5.0L/5.7L PFI TESTS W/CODES»(ref-94913)
11. For 5.7L PFI, see: «5.0L/5.7L PFI TESTS W/CODES»(ref-94913)
12. For Cadillac Brougham, see: «CCC V8 CARBURETOR TESTS W/CODES»(/cadillac/brougham/i-1987-1992/remont/testing-diagnostics/#ccc-v8-carburetor-tests-wcodes)
13. For All other Cadillac with DFI, see: «DFI TESTS W/CODES»(ref-58101)

See also:
• TROUBLE SHOOTING - BASIC PROCEDURES
• CCC V8 CARBURETOR TESTS W/CODES