Oil Pressure Gauge Pegged HI

[meridian6]

Have a 92, LT1 (P) with 60K miles. Out of the blue the analog gauge in the cluster pegged on the Hi side. No apparent high pressure symptoms from engine.

After turning off, guage dropped to 80 but as soon as ignition is turned on, it pegs out on HI side of gauge without engine running.
There are Two pressure sending units near rear of engine by center of firewall.
There is a tall (longer) (3 Blade connector) unit that stands almost straight up and a smaller (shorter) ( 1 Blade connector) unit that comes out of the same fitting on a horizontal angle.
WHICH ONE OF THESE is most likely the culprit? Is is it my cluster guage?? HELP-p-p-p-p-p! Thanks.

 

[c4cruiser]

The sensor that is pointing upwards is the oil pressure sending unit. The horizontal sensor is the fuel pump cutoff switch (if oil pressure drops below a certain level, this switch cuts off power to the fuel pump.

You might try replacing the oil pressure sending unit to see if that makes a difference, but first check the connector; a short to ground on this wire may cause the gauge to move to the extreme end of the scale.

The pointers on the gauges are only press-fit to the shaft on the gauge unit. So it's possible that some extreme movement of the needle may have caused the pointer to rotate on the shaft and that may be why the pointer is showing 80 with the ignition off.

Try removing the connecting wire from the oil pressure sending unit (not the fuel pump one!!) and turn the ignition to "Run" and see what the gauge does. Then start the car to see if there is any change. With the wire off, the needle should not move from it's resting position.

 

[meridian6]

With the connector off, ignition off, the guage rests at 80, ignition to run and the guage pegs to HI side, start engine, guage stays at HI side. driving and shifting, it stays pegged out with connector disconnected (same as when connected). There are three wire to this connector that run right into wiring harness?

 

[c4cruiser]

Here's what my 92 does: When I shut the engine off, the needle will stay at the last pressure reading that the oil pressure sender passes to the ECM. When I turn the key to the run position, the needle drops to zero (all the way to the left side of the gauge). If I turn the key off without starting the engine, the needle stays at the zero position.

Once the engine starts, the needle moves to whaever pressure the sending unit reports and with my car with cold oil, that's about 65 psi. When I shut teh engine off, the needle stays at whatever position it was at with the engine running.

It sounds like the gauge is working but the needle may have moved on the shaft. Removing the gauge cluster is a PITA but it can be done. There are aftermarket gauge faces available so removing the needles is necessary to install them. So you can remove and reset the needle position.

 

[meridian6]

This sounds good in theory, but something must have made the needle spike to to HI side and I should probably try to solve that first. Would you recommend changing out the three wire large vertical sensor first? thanks.