Troubleshooting Low Oil Pressure Problem 944

[mothman52]

I need some assistance trying to figure out my low oil pressure reading on my 1986 944NA.

SHORT VERSION: Is a 98.4 ohm reading for the grounded BLUE/WHITE wire disconnected from the G terminal for the Oil Pressure Sensor normal? With the wire grounded and the ignition ON, the gauge pegs above 5 and resistance reads 98.4.

BACKSTORY: I changed my oil and upon starting up my pressure gauge read ZERO pressure and the red warning light was on. My gauge worked well previously. The car idles and sounds completely normal so I figured the sensor went out and I ordered and installed a new one.

However, surprisingly, the same zero pressure reading at the gauge persisted (The sensor was one of those $20 dollar Uro jobs which I have since discovered have rather spotty quality control; I bit the bullet and ordered an OEM one that is supposed to arrive on January 11.) When I installed the Uro sensor oil did dribble out of the mount, further indication that the pump is actually working and that the trouble lies either in the sensor, the dash gauge, or in the wires between them.

I disconnected and cleaned the 14 pin connector by the firewall and measured the continuity for the BLUE/WHITE wire going to the G terminal on the sensor: It measured 2.4 ohms so the connection there seems sound.

I've pulled the instrument cluster since I wanted to replace some burned out dash bulbs and would test the gauge itself but am not certain how to proceed.

If I know that my resistance reading for the BLUE/WHITE wire was reasonable then I would think that a new sensor will fix my problem. I don't see why simply changing the oil would make my gauge suddenly stop working, but who knows?

So this is where I'm at. Any insight by those more knowledgeable would be greatly appreciated.

[Waz951]

Testing procedure for the oil pressure sensor.


Sensors and Gauges - Information, Troubleshooting, and Testing

[mothman52]

Mucho thanks, Waz...

I was aware of the Clark's Garage post but lacking a potentiometer I was hoping to find out if my resistance reading of the wire leading to the gauge was anywhere within specs without anything else attached to the wire. In other words, what constitutes a "normal" resistance reading? There is no mention what the resistance should be reading with the lead simply disconnected from the sensor and grounded to earth. Since at that point there is no pressure, I would expect a reading of something well under the 29.6 ohms listed on the chart.

I'm a bit mystified as my grounded reading of 98.4 ohms would seem to indicate a reading of around 3 bar on the gauge but it instead pins above 5. Testing the circuit on the back of the cluster gives me an ohm reading of 186 ohms with the needle of the gauge at rest and disconnected from any power source.

So which numbers are the "right" ones? Hence my dilemma.