88 SPFI oil pressure gauge issues.

[TheYeti]

I have an oil pressure gauge that doesn't seem to be working. I did perform a search, but I couldn't find anything related to what I have tried and what I haven't.

 

I have checked to see if the gauge is working by grounding it. It moves up slowly, so I think the gauge is fine.

 

I have replaced the old sending unit and the gauge still doesn't budge.

 

I am at a loss for ideas now. Has anyone had a similar problem?

[azsubaru]

Here's a good way to test it, from Mark Humble:

 

One tool you can make to help diagnose gauge problems is to buy two resistors, one 50 ohm and one 80 ohm, 1/4 watt. Connect one lead from each resistor together and attach a 12" black wire to this connection and solder them together. Then solder a red wire to the 50 ohm resistors other lead. Solder a blue wire to the 80 ohm resistor and attach alligator clips to the ends of each wire. To keep the resistors from getting damaged, put them in a short peice of PVC pipe and fill with silicon.

 

Now you have a gauge tester that can be used on almost anything. To use, connect the black lead to ground and the blue to the sensor wire to be tested and turn on the ignition. The gauge should about 1/3 up the scale. If no reading, repeat the test at the gauge. This is done to check the wire between the gauge and the sending unit. If still no reading, use a volt meter or test light to check for power to the gauge, if there is power, but no reading, the gauge is bad. The red wire is used to water temp.

 

Hook the blue wire up out at the sending unit, and if the guage works, you've narrowed it down to the sending unit.