Oil Pressure Sender – Bench Test

Overview

This procedure outlines how to bench test the oil pressure sending unit on a Porsche 944 (16v engine) using a handheld air pump to simulate oil pressure. By applying controlled pressure and measuring the sender’s resistance, you can verify if it accurately responds to pressure changes, ensuring reliable oil pressure readings on the dashboard gauge. This test is critical for diagnosing faulty senders, which can cause incorrect gauge readings and potentially mask serious engine issues.

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

Tools Required

• Multimeter (with Auto Ranging functionality)
• Test leads kit
• Handheld air pump with pressure gauge (capable of 0–5 bar/0–72.5 psi)
• Useful alternative to air pump: Cooling System Pressure Tester (only up to 2.5 bar/35 psi)
• Hose (19mm (3/16″) Inner Diameter to connect to sender)
• Hose clamps to fit over hose (25mm (1″) Outer Diameter)
• Wrench (22 mm/0.87 inches, to remove/install sender)
• Vise or clamp (optional, to secure sender)

Parts Required

• Oil Pressure Sending Unit [if faulty] (944 606 203 00)
• Crush washer for sender (if reinstalling or replacing)

Step-by-Step Procedure

Step 1: Remove the Oil Pressure Sending Unit

1. Park the Porsche 944 on a level surface, engage the parking brake, and ensure the engine is off and cool to avoid burns or oil spillage.
2. Locate the oil pressure sending unit on the engine block, near the oil filter housing (typically on the driver’s side).
3. Disconnect the electrical leads (blue + blue and white wires) from the sender. Note their orientation for reconnection.
4. Use a 22 mm (0.87 inches) wrench to carefully loosen and remove the sender from the engine block. Place a rag underneath to catch any dripping oil.
5. Clean the sender’s threaded port with a rag and inspect for damage, corrosion, or debris. Set the sender aside on a clean surface.

Step 2: Set Up the Test Apparatus

6. For Handheld Air Pump AND Pressure Tester Pump:

Press hose over the threaded end of the sender. Clamp down using a hose clamp.

Insert rubber cone adapter from the kit into the other end of the hose. Clamp down using a hose clamp.

Attach choice of pump to the rubber cone adapter.

7. Optionally, secure (do not over tighten) the sender in a vice or clamp to prevent movement during testing. Ensure the vice is padded to avoid damaging the sender.
8. Verify that the pump’s pressure gauge is functional and reads accurately up to 5 bar (72.5 psi).

Step 3: Connect the Multimeter

9. Set the multimeter to measure resistance (ohms) in the 0–500 ohm range.
10. Connect the multimeter’s positive lead to the sender’s signal terminal (terminal “G,” where the blue and white wire was attached).
11. Connect the negative lead to the sender’s ground (the threaded metal housing). Ensure a clean, secure connection for accurate readings.
12. Test the multimeter connection by checking for a stable reading (e.g., a fluctuating or infinite reading indicates a loose connection).

Step 4: Apply Pressure and Measure Resistance

13. Start with no pressure (0 bar) and record the baseline resistance. Expect a low value (e.g., 0–10 ohms, depending on the sender’s design).
14. Slowly apply pressure using the pump, targeting 1 bar (14.5 psi). Pause to let the pressure stabilize, then record the resistance.
15. Repeat for 2 bar (29.0 psi), 3 bar (43.5 psi), 4 bar (58.0 psi), and 5 bar (72.5 psi), recording resistance at each point.

Pressure Conversion Reference:
1 bar = 14.5 psi

2 bar = 29.0 psi

3 bar = 43.5 psi

4 bar = 58.0 psi

5 bar = 72.5 psi

Caution: Apply pressure gradually to avoid damaging the sender’s internal mechanism. Do not exceed 5 bar (72.5 psi).

16. Compare measured resistance to the expected values:

Step 5: Evaluate Sender Condition

17. If resistance matches expected values (e.g., ~184 ohms at 5 bar) and changes smoothly with pressure, the sender is functional.
18. If resistance is erratic, stuck (e.g., 890 ohms across all pressures), or significantly deviates from expected values, the sender is faulty.

Common Failure Signs:
High resistance (e.g., >800 ohms) causing the gauge to peg above 5 bar.

No change in resistance, indicating a stuck internal mechanism.

19. Inspect the sender for physical damage, oil leaks, corrosion, or debris in the pressure port. Clean with a rag if needed.

Step 6: Clean Up and Replace if Necessary

20. Slowly release pressure from the pump to avoid sudden decompression.
21. Disconnect the sender from the test apparatus and clean any oil or residue with a rag.
22. If the sender is faulty, replace it with a new unit (944 606 203 00) and a new crush washer.

For Reinstallation:
Screw the sender into the engine block by hand, then torque to 25–30 Nm (18–22 ft-lbs) using a torque wrench.

Reconnect the blue wire and also the blue and white wire, where the blue and white wire is attached to terminal “G,” ensuring a secure connection.

23. If the sender is functional, reinstall it following the same steps, ensuring the crush washer is in good condition or replaced.

Post Procedure Checklist

• Verify the sender is securely installed with no oil leaks at the threads.
• Ensure the electrical lead (blue and white wire) is firmly connected to terminal “G.”
• Start the engine and check the oil pressure gauge for normal readings (e.g., 4.5–5 bar at cold idle, 2.5–3 bar at warm idle).
• Inspect the test area for tools or debris left behind.
• Dispose of any used oil per local regulations.

Sources

• Pelican Parts
• YouTube