Chrysler Repair: 91 New Yorker 5th Ave Oil Pressure Unit, gaige, oil pressure

Question
Hi Roland,
My 91 NY 5th Ave oil pressure gaige is erratic - guage will say good pressure and the next second, with no change in RPM/etc, says zero oil pressure.  I hear no lifters or other tapping that usually indicates oil pressure issues.  I am considering installing a new (after market) sending unit and guage, but I cannot find where on the engine the sending unit is.  Can you tell me where the sending unit is, and is the behavior of the guage typical of a bad.clogged unit, or is the engine/oil pump gone?  Would a new unit help diagnose, or am I wasting time & money?

Many thanks,
Bryan

Answer
Hi Bryan,
The sending unit is usually on the side of the engine facing the front of the car, near the oil filter and dipstick tube (you didn't mention if you have the 2.5, 3.0, 3.3, or 3.8L engine). It has two wires, gray/yellow and gray. The gray/yellow is for oil pressure. the gray is for the warning light. You could check the resistance of the pin that accepts the gray/yellow to ground (the shell of the unit) when the reading drops to zero with the engine running. If it is infinite, then that shows the circuit to the gauge is OK, but the sensor could be faulty IF you truly have pressure.
When you have pressure, the sender should read 30-35 ohms depending on rpm. The problem is to read the pressure and the resistance at the same time which would require a T-fitting and a separate oil pressure gauge. My inclination would be to replace the sending unit after verifying that the wires are OK. Then if it continues investigate with an actual pressure gauge. It is doubtful that the pump stops completely.
Roland