Ignition System - Direct Ignition System (dis) Buick Skylark VI

DESCRIPTION

The Direct Ignition System (DIS) is a distributorless system used on 2.0L (VIN 1), 2.5L, 2.8L and 3.1L equipped models. The 2.3L system is referred to as the Integrated Direct Ignition (IDI) system. The operation of both systems is quite similar to that of the C(3)I system. System consists of 2 or 3 ignition coils (4-cylinder or V6), spark plug wires, ignition module (located under coil pack), a crankshaft position sensor, necessary wiring and the Electronic Spark Timing (EST) portion of the Electronic Control Module (ECM). On 2.3L models, coils, module and spark plug connectors are all combined in one unit which plugs directly onto spark plugs.

This system utilizes the EST signal from the ECM to control spark timing. Ignition timing is controlled by the ECM using information from the following inputs: crankshaft position, engine RPM, engine temperature, engine load (manifold pressure or vacuum), air temperature and atmospheric pressure.

IGNITION MODULE

Rather than a crankshaft position sensor mounted at crankshaft pulley (C(3)I), spark is timed by a signal sent from a crankshaft sensor mounted in side of block. This signal is received by ECM (through ignition module) and is used to trigger each coil at the proper time. In the DIS, each cylinder is paired with the cylinder opposite it in the firing order. The spark occurs simultaneously in the cylinder coming up on the compression stroke and in the cylinder coming up on the exhaust stroke. The process is repeated when the cylinders reverse roles.

Each cylinder pair is fired by its own ignition coil. On the 2.0L, 2.3L and 2.5L engines, cylinders No. 1-4 and 2-3 are paired together. On 2.8L and 3.1L engines, cylinders No. 1-4, 3-6 and 2-5 are paired together.

During cranking (and less than 400 RPM), the ignition module monitors crankshaft sensor synchronization pulse to begin ignition firing sequence (1/4 coil pair). The ignition module is incorporated into the coil pack. (Scheme 1)- (Scheme 4).

Scheme 1

Scheme 2

Scheme 3

Scheme 4

ELECTRONIC SPARK TIMING (EST)

The EST system uses the same EST-to-ECM wiring circuits as the HEI-EST distributor type ignition system uses. Operation of each circuit is described in the following paragraphs.

IGNITION REFERENCE SIGNAL

The crankshaft position sensor sends a signal to the DIS ignition module which results in a reference signal being sent to the ECM. The ECM uses this signal to calculate the crankshaft position and engine RPM. This signal is used as a "trigger" for firing fuel injectors. If RPM reference is not present, vehicle will not run.

BY-PASS SIGNAL

When engine speed is less than 400 RPM, the ignition module controls spark using a predetermined interval based on engine speed alone. When engine speed is greater than 400 RPM, the ECM applies 5 volts to the by-pass circuit to switch spark timing control from the DIS module to the ECM. On open or grounded by-pass circuit will cause the engine control system to operate in an ignition timing back-up mode. A code 42 will be set.

EST SIGNAL

When in the EST mode, ECM controls EST and compensates for all driving conditions. If ECM has an internal failure of the EST system, this will cause ECM to operate in an ignition timing back-up mode. The "SERVICE ENGINE SOON" light will illuminate. If the EST fault is present the next time the engine is started, Code 42 will be set. An open or grounded EST circuit will cause engine to stall. Engine will restart; however, engine will stall again once by-pass line tries to reactivate EST mode.

REFERENCE GROUND

The EST system is grounded through the DIS ignition module to ensure that the ground circuit does not have excessive amount of voltage drop between the ignition module and the ECM. An excessive voltage drop in the system could affect engine performance.

IGNITION COILS

Separate ignition coils are mounted over the DIS ignition module. Each coil provides the spark for 2 simultaneously paired spark plugs. Each coil can be replaced separately.

CRANKSHAFT POSITION SENSOR

The crankshaft position sensor is mounted on the bottom of the DIS ignition module or near the ignition module. (Scheme 1)- (Scheme 4). The sensor protrudes through the side of engine block and is mounted within.050" (1.3 mm) of an internally-mounted crankshaft reluctor ring. Sensor position is not adjustable.

The reluctor is a special piece of metal cast with the crankshaft. It has 7 slots machined into it, 6 of which are equally spaced (60 degrees apart). A seventh slot is spaced about 10 degrees from one of the other slots and generates a synchronization pulse signal. As crankshaft rotates, notches in the reluctor ring change the magnetic field at the tip of position sensor. This creates an induced AC voltage signal in the sensor windings, resulting in RPM reference signals which are sent to ECM by ignition module. This allows ECM to compute crankshaft position and RPM, and fire appropriate ignition coil at the proper time.

TROUBLE SHOOTING

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

TESTING & DIAGNOSIS

Ignition system is an integral part of the engine's computerized engine control system. See appropriate TESTS W/CODES article in the ENGINE PERFORMANCE section for testing and diagnosis information. Refer to the following list.

1. For 2.0L VIN [K], see: «2.0L(K)/2.5L TESTS W/CODES»(/buick/skylark/vi-1986-1992/remont/testing-diagnostics/#20lk25l-tests-wcodes)
2. For 2.0L VIN [1], see: «2.0L VIN [1] TESTS W/CODES»(ref-94905)
3. For 2.5L, see: «2.0L(K)/2.5L TESTS W/CODES»(/buick/skylark/vi-1986-1992/remont/testing-diagnostics/#20lk25l-tests-wcodes)
4. For Beretta & Corsica 2.8L: «2.8L VIN [W] PFI TESTS W/CODES»(ref-94906)
5. For Celebrity, Cutlass Ciera, Cutlass Cruiser & 6000 2.8L, see: «2.8L VIN [W] PFI TESTS W/CODES»(ref-94907)
6. For Cutlass Supreme, Grand Prix & Regal 2.8L, see: «2.8L VIN [W] PFI TESTS W/CODES»(ref-94908)
7. For 3.1L, see: «3.1L VIN [T] PFI TESTS W/CODES»(ref-58099)

Note. To obtain proper RPM readings, use a "Scan" tester connected to the ALDL connector, or use a scope or an inductive tachometer on the 2-cycle scale. If a 2-cycle scale is unavailable, divide 4-cycle reading by 2.

EST PERFORMANCE CHECK

The ECM will set timing at a specified value when ALDL "test" terminal is grounded. To check the EST operation, perform the following steps

1. Start and run engine at 1500 RPM. Ground ALDL "test" terminal. When "test" terminal is grounded there should be a noticeable change in engine RPM. When a fault in the EST system occurs, a Code 42 should be set.
2. If a Code 42 (or 43) is set, use appropriate CODE chart below for diagnosis. If symptom is engine miss and the DIS is suspected, use CHART C4M - DIS MISFIRE DIAGNOSIS below for diagnosis.

CHART C4M - DIS MISFIRE DIAGNOSIS

The IDI system uses a waste spark method of distribution. This type of ignition system allows the module to trigger both the No. 1 and No. 4 coil pair, resulting in both No. 1 and No. 4 spark plugs firing simultaneously. No. 1 cylinder is on compression stroke the same time No. 4 is on exhaust stroke, resulting in a lower energy requirement to fire No. 4 spark plug. This allows the remainder of high voltage to be used to fire No. 1 spark plug. On this application, crank sensor is mounted to/and protrudes through the engine block to within about .050" (1.3 mm) of crankshaft reluctor.

Since the reluctor is a machined portion of crankshaft, and sensor is mounted in a fixed position on engine block, timing adjustments are not possible or necessary.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test checks for equal relative power output between the cylinders. Any injector, when unplugged, that does not cause a drop in engine RPM, is responsible for misfire condition.
2. If plug boot is burned, the other plug on that coil may still fire at idle. This step tests system's ability to produce at least 25,000 volts at each spark plug.
3. A coil that has no spark to either spark plug, may have an open secondary circuit. If this condition exists, coil's secondary resistance should be checked. Resistance readings greater than 20,000 ohms, but not infinite, will probably not cause a no-start condition. However, this may cause an engine miss under certain conditions.
4. Test light will blink if no-spark condition is caused by faulty coil connections, coil or secondary boot assembly. If light does not blink, fault is in module connections or module.
5. This step checks for an open injector driver circuit and for ignition voltage feed to the injector.
6. An injector driver circuit shorted to ground would result in test light illumination, and possibly a flooded condition which could damage engine. A shorted injector (less than 2 ohms) could cause incorrect ECM operation.

Chart C4M Schematic - IDI Misfire Diagnosis. Scheme 5

Flow Chart C4M - IDI Misfire Diagnosis. Scheme 6

CODE 42 - EST CIRCUIT OPEN OR GROUNDED

The ignition module sends a reference signal to ECM when engine is cranking. While engine is less than 700 RPM, ignition module controls ignition timing. After engine speed exceeds 700 RPM, ECM sends a 5 volt signal on the by-pass circuit No. 424 to switch timing to ECM control through EST circuit No. 423. An open or ground in the EST or by-pass circuit will set a Code 42 and cause engine to run on module or by-pass timing. This will result in poor performance and poor fuel economy.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test checks to see if ECM recognizes a problem. If a Code 42 has not been set at this point, problem is intermittent and could be result of a loose connection.
2. With ECM unplugged, ohmmeter should read less than 500ohms, which is normal resistance of ignition module. Higher resistance would indicate a fault in circuit No. 423, poor ignition module connection or faulty ignition module.
3. If test light illuminates when connected from 12 volts to ECM harness terminal "BC7", either circuit No. 423 is shorted to ground or ignition module is faulty.
4. Check to see if ignition module switches when by-pass circuit is energized by 12 volts through test light. If module actually switches, ohmmeter reading should shift to greater than 8000 ohms.
5. Unplugging ignition module should cause ohmmeter to read as if it were monitoring an open circuit (infinite reading). If ohmmeter has a reading other than infinite, circuit No. 423 is shorted to ground.

Diagnostic Aids

An intermittent condition may be caused by a poor connection rubbed through wire insulation, or wire broken inside insulation. Check ECM harness connectors for backed out terminals "BC7" or "BC8". Also check for improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

Code 42 Schematic - EST Circuit Open or Grounded. Scheme 7

Code 42 Flow Chart - EST Circuit Open or Grounded. Scheme 8

CODE 43 - ESC RETARD SIGNAL TOO LOW

The Knock sensor detects engine detonation (vibration). The ECM will retard electronic spark timing based signal being received. The circuitry within the knock sensor causes ECM 5 volts to be reduced so that under a knock condition, circuit No. 496 would measure about 2.5 volts. The knock sensor produces an AC signal which rides on the 2.5 DC voltage. The amplitude and signal frequency are dependent upon knock level. ECM performs 2 tests on this circuit to determine if operation is correct. If either of 2 test fail, a Code 43 will be set. The following are test procedures performed by ECM

1. An indication of knock for 3.67 seconds greater than a 3.9 second interval with engine running.
2. ECM terminal "YD9" voltage is either greater than about 3.75 volts (indicating an open circuit No. 496), or less than about 1.25 volts (indicating circuit No. 496 is shorted to ground) for 5 seconds or more. NOTE: Test numbers refer to test numbers on diagnostic chart. If conditions for test, as described above, are being met, "Scan" tester will always indicate "YES" when knock signal position is selected. If an audible knock is heard from engine, repair internal engine problem so that knock will not take place at idle. If tapping on engine lift hook does not produce a knock signal, try tapping engine closer to sensor before proceeding. ECM has a 5 volt signal through the pull-up resistor, which should be present at knock sensor terminal. This test will determine if knock sensor or ESC portion of MEM-CAL is at fault.

Check circuit No. 496 for possible open or short to ground. Check for proper installation of Mem-Cal. Mechanical engine knock can cause a knock sensor signal. Abnormal engine noise must be corrected prior to diagnosis.

Code 43 Schematic - ESC Retard Signal Too Low. Scheme 9

Code 43 Flow Chart - ESC Retard Signal Too Low. Scheme 10

Removal & Installation (2.0L, 2.5L, 2.8L & 3.1L)

1. Disconnect negative battery cable. Unplug connectors at ignition module. Disconnect spark plug wires from coil pack. Remove ignition module from engine block. Remove coils and assembly plate.
2. On 2.5L engines, inspect crankshaft sensor "O" ring for wear, cracks or other damage. (Scheme 2) Replace if necessary. Lubricate new "O" ring with engine oil before installing.
3. To install, reverse removal procedures. Tighten ignition coil nuts and module to specification. See «TORQUE SPECIFICATIONS»(/buick/skylark/vi-1986-1992/remont/ignition-system/#ignition-system-direct-ignition-system-dis__torque-specifications) in this article.

Note. If spark plug boots adhere to spark plugs, use Boot Remover (J-36011). Twist first and then pull upward. Boots must be in place on housing prior to ignition system assembly installation or damage may result.

Removal & Installation (2.3L)

1. Disconnect negative battery cable. Disconnect 11-pin harness connector. Remove 4 ignition assembly cover-to-cam carrier bolts. (Scheme 5)
2. Remove ignition system assembly from engine. Remove 4 housing cover screws. Remove housing cover. Remove coil harness connector from module. Remove module-to-cover screws. Remove module from cover. To install, reverse removal procedures. See «TORQUE SPECIFICATIONS»(/buick/skylark/vi-1986-1992/remont/ignition-system/#ignition-system-direct-ignition-system-dis__torque-specifications) in this article.

Note. DO NOT wipe grease from module or coil if module is not being replaced. If a new module is being installed, silicone grease will be included. Spread grease on metal face of module and on the cover where the module seats. This grease is necessary for module cooling purposes.

Scheme 11

Removal & Installation (2.0L, 2.3L, 2.8L & 3.1L)

Disconnect sensor harness at DIS ignition module. Remove bolt and sensor from engine block. (Scheme 3)and (Scheme 4). Inspect crank- shaft sensor "O" ring for wear, cracks or other damage. Replace if necessary. Lubricate new "O" rings with engine oil before installing. To install, reverse removal procedure.

Removal & Installation (2.5L)

Remove DIS ignition module. Remove crankshaft sensor mounting screws and remove sensor from DIS module. Inspect "O" ring for wear, before installing DIS module. Replace if necessary. To install, reverse removal procedure. See TORQUE SPECIFICATIONS in this article.

Disconnect negative battery cable. Remove spark plug wires from coils. Remove nuts or screws from ignition coils. Remove coils. To install, reverse removal procedure.

Disconnect negative battery cable. Disconnect 11-pin harness connector. Remove 4 ignition cover-to-cam carrier bolts. (Scheme 5) Remove ignition system assembly from engine. Remove 4 housing cover screws. Remove housing cover. Remove coil harness connector from module. Remove module-to-cover screws. Remove module from cover. To install, reverse removal procedures. See TORQUE SPECIFICATIONS in this article.

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

See also:
• TROUBLE SHOOTING - BASIC PROCEDURES
• 2.0L(K)/2.5L TESTS W/CODES
• TORQUE SPECIFICATIONS