Electronic Ignition (EI) System. Pontiac Grand Prix 1996

For 1990-2009 cars only

Makes 🢒 Pontiac 🢒 1996 🢒 Grand Prix 🢒 Engine 🢒 Engine Controls - 3.4L (VIN X) 🢒 Electronic Ignition (EI) System

Purpose

The electronic ignition system controls fuel combustion by providing a spark to ignite the compressed air/fuel mixture at the correct time. To provide optimum engine performance, fuel economy, and control of exhaust emissions, the PCM controls the spark advance of the ignition system. Electronic ignition has the following advantages over a mechanical distributor system:

•	No moving parts.

•	Less maintenance.

•	Remote mounting capability.

•	No mechanical load on the engine.

•	More coil cool down time between firing events.

•	Elimination of mechanical timing adjustments.

•	Increased available ignition coil saturation time. Increased available ignition coil saturation time.

Operation

The electronic ignition system does not use the conventional distributor and coil. The ignition system consists of three ignition coils, an ignition control module, a dual Hall-effect crankshaft position sensor, an engine crankshaft balancer with interrupter rings attached to the rear, related connecting wires, and the Ignition Control (IC) and fuel metering portion of the PCM.

Conventional ignition coils have one end of the secondary winding connected to the engine ground. In this ignition system, neither end of the secondary winding is grounded. Instead, each end of a coil's secondary winding is attached to a spark plug. Each cylinder is paired with the cylinder that is opposite it (1/4, 2/5, 3/6). These two plugs are on companion cylinders, i.e., on top dead center at the same time. When the coil discharges, both plugs fire at the same time to complete the series circuit. The cylinder on compression is said to be the event cylinder and the one on exhaust is the waste cylinder. The cylinder on the exhaust stroke requires very little of the available energy to fire the spark plug. The remaining energy will be used as required by the cylinder on the compression stroke. The same process is repeated when the cylinders reverse roles. This method of ignition is called a waste spark ignition system.

Since the polarity of the ignition coil primary and secondary windings is fixed, one spark plug always fires with normal polarity and its companion plug fires with reverse polarity. This differs from a conventional ignition system that fires all the plugs with the same polarity. Because the ignition coil requires approximately 30% more voltage to fire a spark plug with reverse polarity, the ignition coil design is improved, with saturation time and primary current flow increased. This redesign of the system allows higher secondary voltage to be available from the ignition coils - greater than 40 kilovolts (40,000 volts) at any engine RPM. The voltage required by each spark plug is determined by the polarity and the cylinder pressure. The cylinder on the compression stroke requires more voltage to fire the spark plug than the cylinder on the exhaust stroke.

It is possible for one spark plug to fire even though a plug wire from the same coil may be disconnected from its companion plug. The disconnected plug wire acts as one plate of a capacitor, with the engine being the other plate. These two capacitor plates are charged as a spark jumps across the gap of the connected spark plug. The plates are then discharged as the secondary energy is dissipated in an oscillating current across the gap of the spark plug that is still connected. Secondary voltage requirements are very high with an open spark plug or spark plug wire. The ignition coil has enough reserve energy to fire the plug that is still connected at idle, but the coil may not fire the spark plug under high engine load. A more noticeable misfire may be evident under load; both spark plugs may then be misfiring.

System Components

Crankshaft Position Sensor and Crankshaft Balancer Interrupter Rings

The 24X crankshaft position sensor, secured in an aluminum mounting bracket and bolted to the front left side of the engine timing chain cover, is partially behind the crankshaft. A 3-wire harness connector plugs into the sensor, connecting it to the Powertrain Control Module (PCM). The 24X crankshaft position sensor contains one Hall-effect switch and magnet. The magnet and Hall-effect switch are separated by an air gap. A Hall-effect switch reacts like a solid state switch, grounding a low current signal voltage when a magnetic field is present. When the magnetic field is shielded from the switch by a piece of steel placed in the air gap between the magnet and the switch, the signal voltage is not grounded. If the piece of steel (called an interrupter) is repeatedly moved in and out of the air gap, the signal voltage will appear to go ON-OFF-ON-OFF-ON-OFF. Compared to a conventional mechanical distributor, this ON-OFF signal is similar to the signal that a set of breaker points in the distributor would generate as the distributor shaft turned and the points opened and closed. In the case of the electronic ignition system, the piece of steel is the concentric interrupter ring mounted to the rear of the crankshaft balancer . The interrupter ring has blades and windows that, with crankshaft rotation, either block the magnetic field or allow it to close the Hall-effect switch. The Hall-effect switch produces a signal called the CKP 24X because the interrupter ring has 24 evenly spaced blades and windows. When a CKP 24X interrupter ring window is between the magnet and Hall-effect switch, the magnetic field will cause the CKP 24X Hall-effect switch to ground the CKP 24X signal voltage supplied from the PCM. The CKP 24X portion of the crankshaft position sensor produces 24 ON-OFF pulses per crankshaft revolution. The 24X signal allows the PCM to determine a more precise crankshaft position at lower RPM.

7X Crankshaft Position Sensor/Crankshaft reluctor Wheel

The 7X crankshaft position sensor, a magnetic sensor, is bolted to the lower right side of the engine block. A 2-wire harness connector plugs into the sensor, connecting it to the Ignition Control Module (ICM). The 7X crankshaft position sensor is separated by an air gap from a crankshaft reluctor wheel. The crankshaft reluctor wheel, cast on the crankshaft, has seven machined windows. Six of the machined windows are spaced at regular 60° intervals around the reluctor's circumference. The seventh window is spaced 10° from one of the other windows. As the reluctor wheel rotates with the crankshaft, the machined windows change the magnetic field generated by the 7X crankshaft position sensor. The changed magnetic field induces a voltage signal. The ICM interprets the signal as an indication of crankshaft position. The ICM uses the seventh window as the sync signal. To fire the correct ignition coil, the ICM must see the sync signal.

Camshaft Position (CMP) Sensor

The camshaft position sensor is located on the top of the cylinder head towards #6 cylinder. A 3-wire harness connector plugs into the sensor, connecting it to the Powertrain Control Module (PCM). The PCM applies a signal voltage to the camshaft position sensor. The left bank exhaust camshaft has a toothmachined on the casting. The camshaft position sensor is separated from the exhaust camshaft by an air gap. As the exhaust camshaft rotates, the machined tooth aligns with the camshaft position sensor. The signal voltage to the sensor is pulled low. The PCM interprets the change in signal voltage as an indication of camshaft position. The CAM signal is created as piston #1 is on the intake stroke. If the correct CAM signal is not received by the PCM, DTC P0341 will be set.

Ignition Control Module and Ignition Coil


(1)	Screws
(2)	Ignition Coil
(3)	Ignition Control Module

Ignition Coils

Three twin-tower ignition coils are individually mounted to the ignition control module. Each coil provides spark for two plugs simultaneously (waste spark distribution). Each coil is serviced separately. Two terminals connect each coil pack to the module. Each coil is provided a fused ignition feed. The other terminal at each coil is individually connected to the module, which will energize one coil at a time by completing and interrupting the primary circuit ground path to each coil at the proper time.

Ignition Control Module (ICM)

The ignition control module performs the following functions:

•	It determines the correct ignition coil firing sequence, based on the sequence of 7X crankshaft position sensor pulses. This coil sequencing occurs at start-up. After the engine is running, the module remembers the sequence, and continues triggering the ignition coils in proper sequence.

•	It determines whether or not the crankshaft is rotating in the proper direction, and cuts off fuel delivery and spark to prevent backfiring if reverse rotation is detected.

•

It sends the 3X reference signals to the PCM. The PCM determines engine RPM from this signal. This signal used by the PCM to determine crankshaft speed for Ignition Control (IC) spark advance calculations. The falling edge of each 3X reference signal pulse occurs at a specific time in relation to top dead center of any cylinder. The 3X reference signal sent to the PCM by the ignition control module is an ON-OFF pulse occurring 3 times per crankshaft revolution. The ICM calculates the 3X reference signal from the 7X crankshaft position sensor.


(1)	Knock Sensor (KS) Module Cover
(2)	Connector C1 (Blue)
(3)	Connector C2 (Clear)

Powertrain Control Module (PCM)

The PCM is responsible for maintaining proper spark and fuel injection timing for all driving conditions. Ignition Control (IC) spark timing is the PCM method of controlling spark advance and ignition dwell. To provide optimum driveability and emissions, the PCM monitors input signals from the following components in calculating Ignition Control (IC) spark timing:

•	Ignition Control module (ICM).

•	Engine Coolant Temperature (ECT) sensor.

•	Intake Air Temperature (IAT) sensor.

•	Mass Air Flow (MAF) sensor.

•	Trans Range or PNP inputs from Trans Range switch or Park/Neutral Position switch.

•	Throttle Position (TP) sensor.

•	Vehicle Speed Sensor (VSS) / Trans Output Speed Sensor (TOSS).

The ignition system uses many of the the same ignition module-to-PCM circuits as did previous Delco engine management systems using distributor type ignition. The following describes the PCM to ignition control module circuits:

•

3X reference PCM input - From the ignition control module, the PCM uses this signal to calculate engine RPM and crankshaft position.The PCM compares pulses on this circuit to any that are on the Reference Low circuit, ignoring any pulses that appear on both. The PCM also uses the pulses on this circuit to initiate injector pulses.

•

24X reference PCM input - The 24X reference signal is used to accurately control spark timing at low RPM and allow IC operation during crank. Below 1200 RPM, the PCM is monitoring the 24X reference signal and using it as the reference for ignition timing advance. When engine speed exceeds 1200 RPM, the PCM begins using the, 3X reference signal to control spark timing.

•

Camshaft Position PCM input - The PCM uses this signal to determine the position of the cylinder #1 piston during its intake stroke. This signal is used by the PCM to calculate true Sequential Fuel Injection (SFI) mode of operation. The PCM compares the number of CAM pulses to the number of 24X and 3X reference pulses. If the number of 24X and 3X reference pulses occurring between CAM pulses is incorrect, or if no CAM pulses are received while the engine is running, the PCM will set DTC P0341. If the cam signal is lost while the engine is running the fuel injection system will shift to a calculated sequential fuel injection mode based on the last cam pulse, and the engine will continue to run. The engine can be re-started and will run in the calculated sequential mode as long as the fault is present with a 1 in 6 chance of being correct.

•

Reference low PCM input - This is a ground circuit for the digital RPM counter inside the PCM, but the wire is connected to engine ground only through the ignition control module. Although this circuit is electrically connected to the PCM, it is not connected to ground at the PCM. The PCM compares voltage pulses on the 3X or 24X reference input to those on this circuit, ignoring pulses that appear on both.

•

Bypass signal PCM output - The PCM either allows the ignition control module to keep the spark advance at Bypass Mode 10° BTDC, or the PCM commands the ignition module to allow the PCM to control the spark advance (IC Mode). The ignition control module determines correct operating mode based on the voltage level that the PCM sends to the ignition control module on the bypass circuit. The PCM provides 5 volts on the bypass circuit if the PCM is going to control spark timing (IC Mode). If the PCM does not apply 5 volts to the bypass circuit, or if the ignition control module does not sense the 5 volts, the ignition control module will control spark timing (Bypass Mode).

•

Ignition Control (IC) PCM output - The IC output circuitry of the PCM sends out timing pulses to the ignition control module on this circuit. When in the Bypass Mode, the ignition control module grounds these pulses. When in the IC Mode, these pulses are the ignition timing pulses used by the ignition control module to energize one of the ignition coils. Proper sequencing of the 3 ignition coils, i.e.; which coil to fire, is always the job of the ignition control module.

Ignition System Modes of Operation

Anytime the PCM does not apply 5 volts to the ignition control module bypass circuit, the ignition control module controls ignition by triggering each of the three coils in the proper sequence at a pre-determined dwell, with spark advance fixed at 10° BTDC. This is called Bypass Mode ignition.

When the PCM begins receiving 24X reference and 3X reference pulses, the PCM applies 5 volts to the ignition control module bypass circuit. This signals the ignition control module to allow the PCM to control the dwell and spark timing. This is IC Mode ignition. During IC Mode, the PCM compensates for all driving conditions.

In the IC Mode, the ignition spark timing and ignition dwell time is fully controlled by the PCM. The ignition control module is responsible for proper ignition coil sequencing during both Bypass Mode and IC Mode. IC spark advance and ignition dwell is calculated by the PCM using the following inputs:

•	Engine speed (24X reference or 3X reference).

•	Crankshaft position (24X reference or 3X reference and camshaft position PCM input signal).

•	Engine coolant temperature (ECT sensor).

•	Throttle position (TP sensor).

•	Knock signal (Knock sensor).

•	Park/Neutral Position (trans range switch or park/neutral position switch).

•	Vehicle speed (Vehicle Speed Sensor / Trans Output Speed Sensor).

•	PCM and ignition system supply voltage (PCM ignition feed voltage).

Once the change is made to IC Mode, it will stay in effect until one of the following conditions occurs:

•	The engine is turned OFF.

•	The engine quits running.

•	A PCM/IC fault (DTC P1350 or DTC P1361) is detected.

If a PCM/IC fault is detected while the engine is running, the ignition system will switch to Bypass Mode operation. The engine may quit running, but will restart and stay in Bypass Mode with a noticeable loss of performance.

Diagnosis

If the 24X reference signal is not received by the PCM while the engine is running, a DTC P0336 will be set and 3X reference will be used to control spark advance under 1200 RPM, and Bypass Mode will be in effect at under 400 RPM. The engine will continue to run and start normally.

If the 3X reference signal is not received by the PCM while the engine is running, the PCM will use the 24X reference pulses to calculate RPM and crankshaft position. The engine will continue to run and start normally, but DTC P1374 will be set.

Poor engine performance and possibly a MIL with no DTC can be caused If the Reference Low circuit is open or connected to ground at the PCM.

The IC output circuitry in the PCM generates IC output pulses anytime crankshaft reference signal input pulses are being received. When the ignition system is operating in the Bypass Mode (no voltage on the bypass control circuit), the ignition control module grounds the IC pulses coming from the PCM. The ignition control module will remove the ground from the IC circuit only after switching to the IC Mode. The PCM commands switching to IC Mode by applying 5 volts on the bypass circuit to the ignition control module. The PCM monitors its own IC output, and expects to see no pulses on the IC circuit when it has not yet applied 5 volts on the bypass control circuit. When the second 3X reference pulse at the start of crank is seen by the PCM, it applies 5 volts to the bypass control circuit and the IC pulses should no longer be grounded by the ignition control module. The PCM constantly monitors its IC output, and should detect the IC pulses only when commanding the IC Mode. If the IC circuit is open, the PCM will detect IC output pulses while attempting to start the engine (in the Bypass Mode) due to the ignition control module not being able to ground the IC pulses. Three things will occur:

•	DTC P1350 will set.

•	The PCM will not apply 5 volts to the bypass circuit.

•	The engine will start and run in Bypass Mode.

If IC circuit is grounded, the PCM would not detect a problem until the change to IC Mode is commanded by the PCM. When the PCM applies 5 volts to the bypass control circuit, the ignition control module will switch to IC Mode. With the IC circuit grounded, there would be no IC pulses for the ignition control module to trigger the ignition coils, and the engine may falter. The PCM will quickly revert back to Bypass Mode (turn OFF the 5 volts on the bypass circuit), DTC P1361 will set, and the ignition system will operate in Bypass Mode until the fault is corrected and the engine is stopped and restarted.

If bypass circuit is open or grounded, the ignition control module cannot switch to IC Mode. In this case, the IC pulses will stay grounded in the ignition control module, and DTC P1361 will be set. The engine will start and run in Bypass Mode.

The following information will list important considerations to aid the technician in servicing the ignition system.

•	The ignition coils secondary voltage output capabilities are very high - more than 40,000 volts. Avoid body contact with ignition high voltage secondary components when the engine is running, or personal injury may result!

•

The 7X crank sensor is the most critical part of the ignition system. If the sensor is damaged so that the crank sensor pulses are not generated or received by the ignition control module, the engine will not start. There are 2 circuit wires connecting the 7X crankshaft position sensor to the ignition control module. If there is a problem with the wiring or crank sensor connections, the engine will not start (no spark and no injector pulses). If a fault occurs while the engine is running, the vehicle will stall and not restart.

•	The 24X Crankshaft position sensor clearance is very important! The sensor must not contact the rotating interrupter rings at any time, or sensor damage will result. If the balancer interrupter rings are bent, the interrupter ring blades will destroy the sensor.

•	Ignition timing is not adjustable. There are no timing marks on the crankshaft balancer or timing chain cover.

•	If the 24X crankshaft position sensor replacement is necessary, the crankshaft balancer must be removed first. The balancer is a press fit onto the crankshaft; removing the serpentine accessory drive belt and balancer attaching bolt will allow its removal with special tool J 38197.

•	When reinstalling, torque the balancer attachment bolt. This is critical to ensure the balancer stays attached to the crankshaft.

•	If a 24X crankshaft position sensor assembly is replaced, check the crankshaft balancer interrupter rings for any blades being bent. If this is not checked closely and a bent blade exists, the new crankshaft position sensor can be destroyed by the bent blade with only one crankshaft revolution!

•	Neither side of the ignition coil primary or secondary windings is connected to engine ground. Although the ignition coil packs are secured to the ignition control module, it is not an electrical connection to ground.

•

Be careful not to damage the secondary ignition wires or boots when servicing the ignition system. Rotate each boot to dislodge it from the plug or coil tower before pulling it from either a spark plug or the ignition coil. Never pierce a secondary ignition wire or boot for any purpose! Future problems are guaranteed if pinpoints or test lights are pushed through the insulation for testing.

•	The ignition control module is grounded to the engine block through a ground wire to the ignition control module bracket mounting stud. If servicing is required, ensure that good electrical contact is made between the ground and the mounting bracket, including proper hardware and torque.

•	A conventional tachometer used to check RPM on a primary ignition tach lead will not work on this ignition system. To check RPM, use either of the following items:

A tachometer designed with an inductive pickup, used on the secondary side of an ignition system. These tachs are identified by a clamp that goes around a spark plug wire. Set the tach to 2-cycle operation. The 2-cycle setting is required because spark plugs on this engine fire every time the piston is at the top of its stroke. If a 2 cycle selection is not available, divide the indicated 4 cycle reading by 2.

-	A scan tool.