SERVICE MANUAL UPDATE DRIVEABILITY & EMISSIONS CHART

MODELS AFFECTED: 1988 SKYLARKS EQUIPPED WITH 2.3L ENGINE (VIN CODE D)

This bulletin serves to revise the facing page art and the charts for Chart A-3 "Engine Cranks But Won't Run" (Page 1 of 3) (Page 2 of 3) and (Page 3 of 3) in Section 6E3 "Driveability And Emissions" of the 1988 Skylark Chassis Service Manual equipped with 2.3L engines (VIN Code D).

This clarifies Injector Driver Circuits and IDI Connector Pin labeling.

ENGINE CRANKS BUT WON'T RUN 2.3L (VIN D) "N" SERIES (PORT) Condition:

Engine cranks but won't run, or engine may start, but immediately stops running. Battery condition and engine cranking speed are OK and there is adequate fuel in the tank. Circuit Description:

This engine is equipped with a distributorless ignition system called the "Integrated Direct Ignition" system (IDI). The primary circuit of the IDI consists of two separate ignition coils, an IDI (ignition) module and crankshaft sensor as well as the related connecting wires and the EST (electronic spark timing) portion of the ECM. The secondary circuit consists of the secondary winding of the coil, two connecting metal strips molded into the coil housing, the spark plug boot/connector assemblies and spark plugs.

Test Description: Numbers below refer to circled numbers on the diagnostic chart.

1. This step verifies that "SES" light operation, on-board diagnostics, cranking rpm, TPS and coolant sensor signals are normal. A blinking test light verifies that the ECM is receiving the IDI reference signal and attempting to activate the injectors.

2. This step checks injector harness and injectors for opens or shorts. Resistance should measure half that of one injector due to parallel circuit.

3. By installing spark plug jumper leads and testing for spark on two adjacent plug leads (do not use 2 & 3 as they are on same coil), each ignition coil's ability to produce at least 25,000 volts is verified.

4. Checks to see if fuel pump and relay are operating correctly (fuel pump only "ON" 2-3 seconds) and fuel pressure is within proper range.

5. If module can make the test light blink, the fault is coil harness or connections. If not, module or it's connections are faulty.

6. This step determines whether harness or injector is cause of incorrect resistance. Nominal injector resistance is 1.9 to 2.1 ohms at 60 DEG C (140 DEG F). Resistance will increase slightly at higher temperatures.

Diagnostic Aids:

Check For:

- TPS binding or sticking in wide open throttle position or intermittently shorted or open. - Water or foreign material in fuel. - Low Compression. (Timing chain failure) - Verify that only resistor spark plugs are used.

ENGINE CRANKS BUT WON'T RUN 2.3L (VIN D) "N" SERIES (PORT) Condition:

Engine cranks but won't run, or engine may start, but immediately stops running. Battery condition and engine cranking speed are OK and there is adequate fuel in the tank. Circuit Description:

This engine is equipped with a distributorless ignition system called the "Integrated Direct Ignition" system (IDI). The primary circuit of the IDI consists of two separate ignition coils, an IDI ignition module and crankshaft sensor as well as the related connecting wires and the EST (electronic spark timing) portion of the ECM. Each secondary circuit consists of the secondary winding of the coil, two connecting metal strips molded into the coil housing, the spark plug boot/connector assemblies and spark plugs.

Test Description: Numbers below refer to circled numbers on the diagnostic chart.

7. Battery voltage should be available at cavity "A" whenever the fuel pump power feed circuit is switched "ON". The ECM should switch the fuel pump "ON" for 2-3 seconds after ignition is turned "ON" (and when ECM is receiving ignition reference pulses, as while cranking or running). The ignition must be turned "OFF" for at least 10 seconds to assure that the ECM powers down and will then switch the fuel pump back "ON" for 2-3 seconds when ignition is turned back "ON".

8. Light "ON" one circuit only indicates power is available at cavity "A", but grounded circuit is not being completed on the other circuit. This could be due to open circuit or ECM not switching the injector driver circuit to ground.

9. Steady light indicates ground circuit is always completed and is not being switched. This could be due to short to ground in circuit, or faulty ECM injector driver.

10. The fuel pump should be switched "ON" by the ECM for 2-3 seconds after ignition is first turned "ON". It is necessary to turn the ignition "OFF" for at least 10 seconds to assure that the ECM powers down and will then switch the fuel pump back "ON". If the fuel pump operates, but power is not available at injector harness, circuit must be open. If the fuel pump does not operate, CHART A-5 should be used to diagnose the cause.

ENGINE CRANKS BUT WON'T RUN 2.3L (VIN D) "N" SERIES (PORT)

Circuit Description:

The "Integrated Direct Ignition" system (IDI) uses a waste spark method of distribution. In this type of system the ignition module triggers the #1-4 coil pair resulting in both #1 and #4 spark plugs firing at the same time. #1 cylinder is on the compression stroke at the same time #4 is on the exhaust stroke, resulting in a lower energy requirement to fire #4 spark plug. This leaves the remainder of the high voltage to be used to fire #1 spark plug. On this application, the crank sensor is mounted to, and protrudes through the block to within approximately 0.050" of the crankshaft reluctor. Since the reluctor is a machined portion of the crankshaft and the sensor is mounted in a fixed position on the block, timing adjustments are not possible or necessary.

Test Description: Numbers refer to circled numbers on the diagnostic chart.

11. Battery voltage should be available at terminal "L" of the IDI 11 pin connector, and terminal "K" should be a good ground.

12. The test light to 12V simulates a reference signal to the ECM which will result in an injector test light blink for every other touch of the test light, if CKT 430, the ECM and the injector driver circuit are all functioning properly.

13. The crankshaft sensor should output a voltage as the crankshaft turns. If no voltage is produced, the indication is a poor sensor connection or faulty sensor.

14. The crank sensors core is a magnet, therefore, it should be magnetized and the resistance should be within a range of 500 to 900 ohms.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.