Changing Spark Plugs / Checking the Condition of the Spark Plugs

Overview

This procedure guides you through replacing the spark plugs on your Porsche 944 S / S2 (16v engine) and checking their condition. Spark plugs are critical for engine performance, ensuring proper combustion. Regular replacement and inspection can prevent misfires, hesitation, or poor fuel economy.

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Tools Required

• Spark plug socket (typically 21mm or 13/16 inch for the Porsche 944 S / S2)
• Ratchet
• Torque wrench

Parts Required

• Spark plugs (Bosch recommended for the Porsche 944 S / S2, 944 602 115 00)
• Engine oil (small amount for coating threads)

Step-by-Step Procedure

Step 1: Check the Spark Plug Gap

1. Before installing new spark plugs, check the gap using a feeler gauge. Bosch plugs for the Porsche 944 S / S2 are usually pre-gapped, but always verify.
2. Ensure the gap measures between 0.7 to 0.8 mm (0.028 to 0.031 inches). Adjust if necessary using a gapping tool.

Step 2: Prepare the New Spark Plugs

3. Lightly coat the threads of each new spark plug with engine oil to ease installation and prevent seizing.

Step 3: Remove and Replace the Spark Plugs

4. Locate the spark plug wires on the Porsche 944 S / S2’s 16v engine. Disconnect the first spark plug wire by gently twisting and pulling it off. Work on one plug at a time to avoid mixing up the firing order.
5. Use a spark plug socket and ratchet to remove the old spark plug from the cylinder head.
6. Install the new spark plug by hand to avoid cross-threading, then tighten it using a torque wrench to 25 to 30 Nm (18 to 22 ft-lbs).
7. Reconnect the spark plug wire, ensuring it clicks fully onto the plug for a secure connection.
8. Repeat steps 4 through 7 for the remaining three spark plugs on the 3.0L engine.

Step 4: Inspect the Old Spark Plugs

9. Examine each removed spark plug to assess its condition using the guide below:

Normal: Brown to grayish-brown color with slight electrode wear.

Carbon Deposits: Dry black buildup indicates a rich mixture or weak spark, potentially causing misfires or hesitation.

Oily Deposits: Wet oil suggests leaking valve seals or worn piston rings, leading to misfires.

Worn Plugs: Brown to grayish-brown with significant electrode wear means replacement was overdue.

Lean Mixture/Hot Plug: White insulator and excessive electrode wear with no deposits indicate a lean mixture or overly hot spark plug heat range.

Heavy Deposits: Tannish buildup points to valve guide seal leaks or gasoline additive accumulation.

Post Procedure Checklist

• Start the engine and listen for smooth idling to confirm proper installation.
• Check that all spark plug wires are securely connected.
• Inspect for any unusual engine noises or misfires after a short test drive of about 5 miles (8 km).

Sources

• Clark’s Garage
• Pelican Parts
• Porsche 944 Workshop Manual, Volume 1
• Youtube