Here's a troubleshooting checklist:
1. Verify Pump Installation: The most likely culprit, even after replacement, is incorrect oil pump installation. Double-check:
* Correct Alignment: Ensure the oil pump is perfectly aligned with the oil pump drive shaft. Misalignment can prevent it from turning properly.
* Drive Shaft Condition: Is the drive shaft itself damaged or bent? A damaged shaft won't effectively turn the pump.
* Pickup Tube: Is the oil pickup tube properly seated and unobstructed? Debris or a kinked tube can prevent oil from reaching the pump.
* Gasket and Seals: Were all gaskets and seals replaced and properly seated during installation? Leaks here will drastically reduce pressure.
2. Oil Pressure Sensor/Gauge: A faulty oil pressure sensor or gauge could give a false reading. Try:
* Testing the Sensor: Use a multimeter to test the sensor's resistance. Compare it to the specifications in your repair manual. A faulty sensor might read zero pressure even if there's oil flowing.
* Borrowing a Gauge: Connect a mechanical oil pressure gauge directly to the engine. This bypasses the electrical system and provides a more accurate reading.
3. Clogged Oil Passages: Even with a new pump, the engine's oil passages could be clogged with sludge or debris. This is less likely if the engine was recently flushed, but:
* Consider a thorough engine flush: This might dislodge any remaining blockage, but doing this *after* a new oil pump is installed is not ideal. (It could spread debris through the new pump.)
4. Oil Filter: Ensure the oil filter is correctly installed and not clogged. A blocked filter can restrict oil flow.
5. Oil Viscosity: Are you using the correct viscosity oil for the engine and operating temperature? Using oil that's too thick can impede flow.
6. Relief Valve: The oil pump's relief valve may be stuck closed or not functioning correctly, preventing the flow of oil.
7. Worn Engine Bearings: If the engine bearings are severely worn, they might require excessive oil pressure to lubricate properly, leaving little to reach the top end of the engine. This is a very serious problem and a likely cause if other checks pass.
Important Considerations:
* Repair Manual: A repair manual specific to your 1998 Pontiac Grand Am 3.1L is essential. It provides detailed diagrams, specifications, and torque values to ensure correct installation and troubleshooting.
* Professional Help: If you're not comfortable with engine repair, it's best to take your vehicle to a qualified mechanic. Running an engine without sufficient oil pressure will cause catastrophic damage.
Remember to check for oil leaks after the repair to rule out any further issues. If you’ve systematically checked these points and still have no oil pressure at the top of the engine, professional help is strongly recommended to prevent major engine damage.
