Basic troubleshooting principles
The function of the ignition system is to provide a properly timed high-voltage spark to the combustion chamber.
^ On DME ignition systems, the crankshaft reference sensor (in the transmission bellhousing) determines the initial crankshaft position and gives the electronic system its baseline ignition timing. Ignition timing is then controlled by the ECM based on engine load, engine speed (using the crankshaft speed sensor), engine temperature, and throttle position.
An engine that starts and runs indicates that the ignition system is fundamentally working—delivering voltage to the spark plugs. A hard starting or poor-running engine, however may indicate a problem with how well the spark is delivered. A faulty coil, cracked or deteriorated spark plug wires, worn or cracked distributor cap or rotor, and worn or fouled spark plugs are all causes of reduced spark intensity and inefficient combustion.
Inefficient combustion can cause serious problems in the catalytic converter. The poorly burned mixture can overload the converter with raw fuel, leading to converter overheating or plugging. An overheated catalytic converter can be a fire hazard.
An engine that has good cranking speed but will not even begin to start may indicate a complete failure of the system to produce spark. Inspect the ignition system visually. Make sure the spark plug wires have not been interchanged. The firing order is given earlier.
If no faults are located, make a basic check to see if spark is being produced as described below under Ignition system quick-check. This will be the most important first troubleshooting step. If a strong spark is observed, then the failure to start is due to another cause, such as no fuel being delivered to the engine.
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