Volkswagen Golf/Jetta/Cabriole 1990-1999

Diagnosis and Testing


Before beginning any diagnosis and testing procedures, visually inspect the components of the ignition system and engine control systems. Check for the following:

Discharged battery
Damaged or loose connections
Damaged electrical insulation
Poor coil and spark plug connections
Ignition module connections
Blown fuses
Damaged vacuum hoses
Damaged spark plugs

When attempting to search for ignition troubles, also keep in mind that various sensor inputs that the ECM employs to calculate timing may affect engine performance.

Ignition system Precautions

Before proceeding with any type of ignition system testing, be sure to follow these important precautions:

Make sure the ignition switch is OFF before connecting or disconnecting any wiring or test equipment.
When cranking the engine without starting, as for a compression test, disconnect the power supply connector (+12V) from the coil to prevent it from receiving voltage. Other methods of disabling the ignition system are not recommended, and may result in electrical system damage.
Always switch the multimeter to the appropriate measuring range BEFORE making the test connections. Use a high-impedance digital multimeter which is designed for testing computerized electrical components.
DO NOT install a standard ignition coil in the system.
DO NOT connect a condenser/suppressor or powered test light to the negative terminal (1) of the ignition coil.
DO NOT connect any 12-volt test instruments to the positive terminal (15) of the ignition coil. The electronic control unit will be permanently damaged.
DO NOT use a standard test light (electric bulb type) on electronic circuits. The high electrical consumption of these test lights can lead to electronic component damage.
DO NOT connect a quick-charger to the battery for more than 1 minute, nor exceed 16.5 volts with the booster.


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Fig. This spark tester looks just like a spark plug, attach the clip to ground and crank the engine to check for spark

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Fig. This spark tester has an adjustable air-gap for measuring spark strength and testing different voltage ignition systems

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Fig. Attach the clip to ground and crank the engine to check for spark

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Fig. This spark tester is the easiest to use just place it on a plug wire and the spark voltage is detected and the bulb on the top will flash with each pulse

The best way to perform this procedure is to use a spark tester (available at most automotive parts stores). Three types of spark testers are commonly available. The Neon Bulb type is connected to the spark plug wire and flashes with each ignition pulse. The Air Gap type must be adjusted to the individual spark plug gap specified for the engine. The last type of spark plug tester looks like a spark plug with a grounding clip on the side, but there is no side electrode for the spark to jump to. The last two types of testers allows the user to not only detect the presence of spark, but also the intensity (orange/yellow is weak, blue is strong).

  1. Disconnect a spark plug wire at the spark plug end.
  3. Connect the plug wire to the spark tester and ground the tester to an appropriate location on the engine.
  5. Crank the engine and check for spark at the tester.
  7. If spark exists at the tester, the ignition system is functioning properly.
  9. If spark does not exist at the spark plug wire, perform diagnosis of the ignition system using individual component diagnosis procedures.

Cylinder Drop Test

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Fig. These pliers are insulated and help protect the user from shock as well as the plug wires from being damaged

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Fig. To perform the cylinder drop test, remove one wire at a time and . . .

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Fig. . . . note the idle speed and idle characteristics of the engine. The cylinder(s) with the least drop is/are the non-contributing cylinder(s)

The cylinder drop test is performed when an engine misfire is evident. This test helps determine which cylinder is not contributing the proper power. The easiest way to perform this test is to remove the plug wires one at a time from the cylinders with the engine running.

  1. Place the transaxle in P , engage the emergency brake, and start the engine and let it idle.
  3. Using a spark plug wire removing tool, preferably, the plier type, carefully remove the boot from one of the cylinders.

Make sure your body is free from touching any part of the car which is metal. The secondary voltage in the ignition system is high and although it cannot kill you, it will shock you and it does hurt.

  1. The engine will sputter, run worse, and possibly nearly stall. If this happens reinstall the plug wire and move to the next cylinder. If the engine runs no differently, or the difference is minimal, shut the engine off and inspect the spark plug wire, spark plug, and if necessary, perform component diagnostics as covered in this section. Perform the test on all cylinders to verify the which cylinders are suspect.