Oil Pressure Sensor

This procedure covers the removal and replacement of the oil pressure sending unit on the 1970 AMC Rebel Machine with 390ci V8 engine.

Warnings

Tools required

Parts

• Oil pressure sending unit × 1 — Standard PS-100 or equivalent single-terminal sender

Preparation

1. Ensure engine is completely cold
2. Disconnect negative battery cable to prevent gauge cluster damage
3. Position drip pan under the work area on passenger side of engine block

Procedure

1. 1

   Locate oil pressure sending unit
   The oil pressure sending unit is located on the passenger side of the 390ci engine block, near the distributor and above the oil filter. It is a small cylindrical component with a single wire terminal on top. Use a flashlight to identify the unit and trace the wire connection.
2. 2

   Disconnect sending unit wire
   Locate the single-blade connector attached to the top terminal of the sending unit. Firmly grasp the connector boot (not the wire) and pull straight up to disconnect. If the connector is corroded or stuck, gently wiggle while pulling to avoid breaking the terminal.
3. 3

   Clean area around sending unit
   Use a wire brush or shop towel to remove dirt, oil buildup, and debris from around the sending unit and the surrounding engine block area. This prevents contamination from entering the oil passage during removal.
4. 4

   Remove oil pressure sending unit
   Using a 1-1/16 inch deep socket or dedicated oil pressure sender socket with ratchet and extension, turn the sending unit counterclockwise to remove. The unit will likely have accumulated oil behind it, so be prepared for spillage. Keep shop towels ready to catch oil as the unit loosens.
5. 5

   Inspect oil passage and threads
   Once the sending unit is removed, inspect the threaded hole in the engine block for debris, metal shavings, or damaged threads. Clean the threads with a shop towel. Verify that oil pressure is present by observing a small amount of oil seepage from the hole (indicates unobstructed oil passage).
6. 6

   Prepare new sending unit
   Apply a small amount of thread sealant with PTFE to the threads of the new sending unit. Use sealant sparingly to avoid excess entering the oil passage. Do not use tape-type thread sealant as pieces can contaminate the oil system.
7. 7

   Install new sending unit
   Thread the new sending unit into the engine block by hand first to ensure proper thread engagement and prevent cross-threading. Once hand-tight, use the socket and ratchet to snug the unit firmly. Tighten until seated but do not over-torque; typical installation is snug plus approximately 1/4 turn. Over-tightening can crack the sending unit or damage block threads.
8. 8

   Reconnect electrical connector
   Push the wire connector firmly onto the terminal of the new sending unit until it clicks or seats completely. Ensure the connection is secure by gently tugging on the wire boot.
9. 9

   Reconnect battery and test
   Reconnect the negative battery cable. Turn the ignition key to the ON position without starting the engine. Observe the oil pressure gauge; it should read zero. Start the engine and verify that the oil pressure gauge reads normal operating pressure (typically 30-50 psi at idle when warm for the 390 V8).

Reassembly

1. Wipe down any spilled oil from the engine block and surrounding components
2. Verify the electrical connector is secure and the wire is properly routed away from hot exhaust components

Verification

• With engine running, confirm oil pressure gauge shows normal reading appropriate for engine temperature and RPM
• Inspect the new sending unit for any oil leaks around the base
• Turn off engine and verify gauge returns to zero with ignition on
• Test drive vehicle and monitor oil pressure gauge for proper operation under various engine loads

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