Hello all, I can't figure out why the gauge in my cluster won't read my oil pressure. I've already replaced the oil pressure sender unit with a OEM replacement and still gauge reads maximum. The gauge itself works, or at least moves to zero when I disconnect a particular wire under the hood, or it reads maximum when connected, there is no in between, max or nothing at all. I keep hearing about a "condenser" that's part of the oil pressure senders electrical circuit, but the Haynes repair manual suggests that this condenser started in 1986, I have 85. I'm running out of clues to get this gauge working.

 

The oil gauge is basically reading a resistance value. This makes it fairly easy to test if you have some typical electronic bits sitting around.

With a multimeter, check the resistance from the cluster input harness to the ground to determine what value the car is actually sending to the gauge.

The expected value range is infinity (gauge at 0), to ~100ohms (gauge max). Any lower value (such as a dead short) or a value that doesn't match up with what you're expecting would indicate a problem before the gauge.

If that looks good, use a resistor from the gauge's oil pressure input to the car's ground. You should see the gauge move in respect to the above ranges. Good test values are 100ohm (gauge max), 140ohm (50%) and 200ohm (25%). When disconnected the gauge should read 0.

If you don't have a box of resistors sitting around, a 1k potentiometer should work as well.

 

if the little black resistor that bolts to the slave cylinder isn't hooked up will make the gauge screwy

 

Great answers. There may be some local help to you as well....
https://www.facebook.com/7sCornerOmaha?fref=ts

 

Thanks guys, I've heard of this little black resistor, Haynes calls it a capacitor, I'll need to perform a hunt for it. By process of elimination that has to be it, gauge is good (full range of movement), oil pressure sender unit is good (zero ohms when not running, and 45-47 ohms when idle) , now need to look for this resistor. Anyone out there have a pic so I know what I'm looking for please? Thanks.

 

By "slave" cylinder, you refer to the clutch, not the brake cylinder correct?

 

Looks like a piece of Black hash with a washer stuck to it...and a wire protruding out of it!

 

yes, brake system doesn't have a slave cylinder, only the clutch system

 

hi! I am having the same problem with my oil pressure gauge being pegged all the way up.
i found a loose wire by the slave, I hooked it up to the frame which made it peg all the way up. Wondering if that ground is supposed to be hooked up somewhere else?

 

The oil pressure sensor does not require a ground. The body of the sensor is grounded by default. Have you looked at the wiring diagram?