COLD STARTABILITY IGNITION DIAGNOSIS

VEHICLES AFFECTED: 1983-84 'J' With 2.0L Engine (VIN Code P), Automatic Transmission, and Federal Emission Systems

Service information manual procedures for diagnosing ignition and EST system faults; including Code 42, cannot be used for vehicles updated per the cold startability special policy adjustment, 84-6-270. Vehicles that have had the cold startability adjustment will never set a code 42, even when an EST or ignition system fault is present. Fault conditions in the EST system can cause symptoms such as spark knock, low power, cranks but will not start, hard start or poor fuel economy with no 'check engine' light and no codes set. The following diagnosis and EST circuit schematic are for vehicles which have been equipped with the cold startability adjustment.

Condition Diagnosis

1. Engine cranks but will 1. Disconnect 'set timing' connector not run or engine starts attempt to start car. If engine but immediately stops. starts, check for an open or short to ground in CKT 423 between the ECM and distributor.

2. Hard start at -23 degrees 2. Check for: C (-10 degrees F) ambient - open CKT 906 between cranking or less. May hear motor and spark bypass relay. metallic 'knock' during - open spark bypass relay ground. crank. - faulty relay (not closing during crank) - on 1983 vehicles with VIN before 418443, check for the presence of an EGR valve vacuum bleed connector (P/N 14079541). Refer to bulletin no. 83-6-218.

3. Spark knocks under heavy 3. Check and not timing. Disconnect loads, loss of 'set timing' connector and again performance and fuel note timing. If there is no change economy. in timing readings: - check for open or short to ground in bypass CKT 424 between the ECM, spark bypass relay, and distributor. - check for relay contacts sticking closed after crank.

In addition to these EST system checks, it is important that the ignition secondary is performing correctly. Check for open or shorted ignition wires, cracked plugs, and other malfunctioning ignition parts.

Be sure that the correct spark plugs (R42CTS, P/N 5614009) have been installed in the vehicle, per the special policy bulletin 84-6-270. If the above procedures do not repair the condition, the cold start kit and EST system are not the cause of the complaint and normal diagnostic procedures should be used to repair the ignition system.

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.