After turbocharging your 240SX, one of the final and crucial tasks is to retard the ignition timing to ensure safe engine operation under boost. This guide will take you through the process, step by step.
Step 1: Warm Up the Engine
Before making any timing adjustments, it’s important to fully warm up the engine. This ensures that all measurements and settings are accurate. Once the engine is warm, shut it off to prepare for the next steps.
Step 2: Disconnect the TPS Harness Connector
Locate the Throttle Position Sensor (TPS) harness connector on the passenger side of the engine, just above the throttle assembly. Disconnect this harness to ensure accurate timing adjustments.
Step 3: Attach the Timing Light
With the TPS harness disconnected, attach a timing light to the number one spark plug wire. Restart the engine and set the timing to 20 degrees BTDC (Before Top Dead Center).
Step 4: Check and Adjust Idle Speed
With the engine running and the timing set, check the idle speed. It should read 650 RPM. If the idle speed is off, adjust the idle screw, which is located on the passenger side of the engine near the firewall, just below the intake manifold. Adjust until the idle speed reaches 650 RPM.
Step 5: Retard the Ignition Timing
To retard the ignition timing:
- Loosen the Distributor Bolts: The distributor (often referred to as the “dizzy”) is secured by two 10mm bolts. Loosen these bolts slightly so you can rotate the distributor.
- Rotate the Distributor: Turn the distributor counterclockwise to retard the timing. For a boost level of 8 psi, a small adjustment of about 2 degrees should be sufficient. This typically requires rotating the distributor approximately 3mm.
- Mark the Distributor Position: Before making adjustments, mark the current position of the distributor with a scribe or paint pen. This allows you to return to the original setting if necessary.
- Verify with the Timing Light: As you rotate the distributor, use the timing light to observe the timing marks on the crank pulley. Adjust until the desired timing is achieved.
Step 6: Final Checks
After setting the timing:
- Stop the Engine: Once you’ve made the adjustments, stop the engine and reconnect the TPS harness connector.
- Restart the Engine and Check Idle: Restart the engine. The idle speed should now read 700 RPM.
- Troubleshooting: If your engine backfires or doesn’t perform well after adjustments, it may indicate that the timing is too retarded or that the distributor is not correctly aligned. This could be due to the distributor being a tooth off, requiring further adjustment. For those running higher boost levels, such as 15 psi, additional timing retard may be necessary as the boost increases.
Conclusion
Retarding ignition timing is a critical step in ensuring the safe operation of a turbocharged 240SX. By carefully following these steps, including proper use of a timing light and attention to idle speed adjustments, you can achieve optimal engine performance. If any issues arise, recheck your adjustments, and ensure that all components are correctly aligned for the best results.