Ignition - Diagnosis If Equipped With Cold Startability

Bulletin No. T 86-56
File in Group 6C
Number 108
Corp. Ref. No. 416301
Date May '86
SUBJECT: IGNITION DIAGNOSIS FOR VEHICLES EQUIPPED WITH COLD STARTABILITY ADJUSTMENT (REFERENCE SPECIAL POLICY ADJUSTMENT BULLETIN, 84-P-1 REISSUE)

MODELS AFFECTED: 1983-1984 CIMARRONS EQUIPPED WITH 2.0L ENGINE (VIN CODE P), AUTOMATIC TRANSMISSION, AND FEDERAL EMISSIONS 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-P-1 reissue. 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.

FIGURE 1:

Condition Diagnosis
(Refer to Figure 1)

1. Engine cranks but will not run 1. Disconnect "set timing" connector. Attempt or engine starts but immediately to start car. If engine starts, check for
stops. an open or short to ground in CKT 423 between
the ECM and distributor.
2. Hard start at -10~F (-23~C) 2. Check for:
ambient or less. May hear - Open CKT 906 between cranking motor and
metallic "knock" during crank. spark bypass relay.
- Open spark bypass relay ground.
- 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. 84-7, Section 6C.

3. Spark knocks under heavy loads, 3. Check and note timing. Disconnect "set loss of performance and fuel timing" connector and again note timing.
economy. If there is no change 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 spark 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-P-1 reissue. 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.