Ignition System Troubleshooting

Overview

This guide helps you diagnose a no-spark condition in your Porsche 944 S / S2 with its 16v engine. If your engine won’t start, and you suspect the ignition system is to blame, this procedure will walk you through checking key components like the distributor cap, rotor, and ignition coil. It’s important because a no-spark condition prevents the engine from running, and pinpointing the issue saves time and money on repairs.

Pink and blue text represents links to additional resources, tools, parts, and partner websites.

Tools Required

• Multimeter
• Test lead jumpers
• 10mm (3/8 inch) wrench (for distributor cap removal)
• Ground wire (for ignition coil test)
• Spark plug (for testing ignition coil output)

Parts Required

• Distributor cap (944 602 901 00) – if replacement is needed
• Distributor cap gasket (944 602 113 00) – if compressed or damaged
• Rotor (944 602 909 00) – if replacement is needed
• Ignition coil (944 602 115 00) – if replacement is needed

Required Additional Procedures

Steps in these procedures are required to complete this process:

• Troubleshooting – Engine Will Not Start
• Distributor Cap Removal

Step-by-Step Procedure

Step 1: Verify No-Spark Condition

1. Before starting, confirm you have a no-spark condition by following this link to ensure this step – Troubleshooting – Engine Will Not Start – of the process is followed accurately.
2. If no spark is confirmed, proceed with the steps below to find the cause.

Step 2: Inspect Distributor Cap and Rotor

3. Grab the distributor cap and try moving it side to side. If it moves easily, tighten the retaining screws with a 10mm (3/8 inch) wrench or replace the distributor cap gasket (944 602 113 00) if it’s worn out.
4. Remove the distributor cap by following this link to ensure this step – Distributor Cap Removal – of the process is followed accurately.
5. Check the distributor cap for cracks, carbon tracks, moisture, debris, a worn rotor button, or damaged terminals. Replace with a new cap (944 602 901 00) if any issues are found.
6. Look at the rotor for charring or pitting. Replace it with a new rotor (944 602 909 00) if damaged.
7. Ensure the rotor’s retaining screw is secure—tighten to 6 Nm (4.4 ft-lbs) if loose, as it can fall out and misalign the rotor.
8. Check that the dust cover behind the rotor is in place. This keeps debris out of the distributor cap, ensuring a strong spark.

Step 3: Test the Ignition Coil

9. Disconnect the ignition coil output wire from the distributor cap.
10. Attach a spare spark plug to the end of the disconnected coil output wire.
11. Connect a ground wire to the spark plug’s threaded metal body.
12. Locate the green wire (negative terminal) on the ignition coil and disconnect it.
13. Connect one end of a ground wire to the ignition coil’s negative terminal where the green wire was.
14. Turn the ignition switch to the ON position (do not start the engine).
15. Tap the loose end of the ground wire on a good ground point, like the battery negative terminal. Watch the spark plug for sparks that match your tapping rhythm.
16. If you see consistent sparks, the ignition coil is working. If not, proceed to the next step to check voltage.
17. Use a multimeter to check for 12 volts DC between the coil’s positive terminal (black wire) and a ground point with the ignition ON. Repeat for the negative terminal (green wire). If voltage is missing, check the wiring; if present but no spark, replace the ignition coil (944 602 115 00).

Step 4: Check Ignition Coil Resistance (Optional)

18. For extra confirmation, test the coil’s primary resistance: connect a multimeter (set to ohms) between the positive (black wire) and negative (green wire) terminals. You should see 0.4 to 0.6 ohms. If outside this range, replace the coil (944 602 115 00).
19. Test the secondary resistance: connect the multimeter between the coil’s output terminal and the negative terminal (green wire). You should see 5000 to 7200 ohms. If not, replace the coil.

Step 5: Check DME Computer Signals

20. If the distributor and coil check out but there’s still no spark, the DME computer or its signals might be the issue. Follow this link to ensure this step.
21. If all inputs are correct but there’s no spark, consider swapping the DME with a known good unit to test. Replacement may be needed if confirmed faulty.

Post Procedure Checklist

• Ensure the distributor cap is secure and doesn’t wobble.
• Verify the rotor spins smoothly and is aligned properly.
• Check that all ignition coil wires are reconnected tightly.
• Start the engine and listen for smooth operation, confirming spark is present.
• Inspect for any loose tools or parts left in the engine bay.

Sources

• Clark’s Garage
• Pelican Parts
• Porsche 944 Workshop Manuals
• YouTube