3.1 Basic Troubleshooting Principles
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, poor spark plug wires, a worn or cracked distributor cap or rotor, and worn or fouled spark plugs are all causes of reduced spark intensity and inefficient combustion. For cars with catalytic converters, this is an especially serious problem since the poorly burned mixture can overload the catalytic converter. This may cause the converter to overheat, causing plugging or presenting 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. A basic check to see if spark is being produced will be the most important first troubleshooting step. If a strong spark is observed, then the failure to start is due to another cause, perhaps incorrect timing or engine mechanical failure.
The TCI-h ignition system contains very sensitive electronic components. To protect the system, and for general safety, the following cautions should be observed during any ignition system troubleshooting, maintenance, or repair work.
CAUTION-
 | Do not touch or disconnect any of the high tension cables from the coil, distributor, or spark plugs while the engine is running or being cranked by the starter. |
| Connect or disconnect ignition system wires, multiple connectors, and ignition test equipment leads only while the ignition is off. |
| Before operating the starter without starting the engine (as when making a compression test), disable the ignition system. On all except CIS-E Motronic and Digifant I, disconnect the wire from the center of the distributor cap and positively connect it to ground on the engine. On Motronic, disconnect the Hall sender connector at the distributor. On Digifant I, disconnect the connector from the coil power stage. Cranking the engine with the high-voltage secondary wiring disconnected may damage the ignition. |
| Do not connect test instruments with a 12-volt current supply to terminal 15 (+) of the ignition coil. The voltage backflow will damage the ignition control unit. In general, make test connections only as specified by Volkswagen, as described in this manual, or as described by the instrument's manufacturer. |
| Do not connect a condenser to terminal 1, the negative (-) coil terminal. This may cause misfiring or ignition system damage. |
| Do not disconnect the battery while the engine is running. |
| The ignition systems in Volkswagens covered by this manual use a special distributor rotor with 1000±400 ohms resistance. Take care to use the correct part. Do not substitute any other Volkswagen or Bosch part. |
| Do not quick-charge the battery (for boost starting) for longer than one minute, and do not exceed 16.5 volts at the battery with the boosting cables attached. Wait at least one minute before boosting the battery a second time. |
| Do not tow a vehicle suspected of having a defective ignition system without first disconnecting the ignition control unit. On Digifant I, disconnect terminal 1 (green) from the coil. |
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CAUTION-
| Do not wash the engine while it is running, or anytime the ignition is switched on. |
| Disconnect the battery when doing any electric welding on the vehicle. |
| Do not try to start the engine of a car which has been heated above 176°F (80°C), (for example, in a paint drying booth) until allowing it to cool to normal temperature. |
| Do not conduct ignition system tests with a test lamp that uses a normal incandescent bulb. The high electrical consumption of these test lamps may damage the electronic components. |
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