VISUAL INSPECTION
Visually inspect all electrical wiring. Look for chafed, stretched, cut or pinched wiring. Ensure electrical connectors fit tightly and are not corroded. Ensure vacuum hoses are properly routed and not pinched or cut. If necessary, see VACUUM DIAGRAMS - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER article to verify routing and connections. Inspect air induction system for possible vacuum leaks.
Diagnosis
- Start engine and allow it to reach normal operating temperature. Increase engine speed to 2000-2500 RPM and note gauge. If reading exceeds 1.25 psi (.09 kg/cm 2 ), exhaust system is restricted.
- Check exhaust system for collapsed pipe, heat distress and possible internal muffler failure. If none of these conditions exist, check for restricted catalytic converter. Replace as necessary.
NO-START DIAGNOSIS
Note. For terminal and circuit identification, see WIRING DIAGRAMS .
- Definition - No start is defined as engine cranks properly, but does not start. Engine may fire a few times.
Scheme 1
Circuit Description
The electronic ignition system uses an individual ignition coil for each cylinder. The PCM controls ignition operation through 6 Ignition Control (IC) circuits. Each ignition coil is connected to PCM, power or ground by following circuits: The ground, ignition 1 voltage and appropriate IC control circuit.
PCM triggers an ignition coil by grounding appropriate IC control circuit using information from Crankshaft Position (CKP) and Camshaft Position (CMP) sensors. (Scheme 1)or see scheme 2.
Diagnostic Aids
The CKP signal is not needed to start and run. Many situations may lead to an intermittent condition. Perform each inspection or test as directed. Remove any debris from connector surfaces before servicing a component. Ensure that gaskets are installed correctly. The gaskets prevent contaminate intrusion. Inspect PCM and engine grounds for clean and secure connections.