Have a 1999 Z71 chev truck with 5.3 L engine that has fluctuating oil pressure. Started with low oil pressure after start with engine clak that disappeared after it warmed up. Changed oil and found sludge in crankcase. cleaned as best we could and blew back through oil filter housing. Now engine shows ''0'' oil pressure after start for about 10 seconds then goes to mid range on gauge. After it warms up, oil pressure starts to drop and engine appears to labour intermittitently.

You checked that you have oil in the engine, right? If not, check it before starting the engine again.

If you are not low on oil, it could be the oil pump that's gone bad, clogged oil filter, or even the oil pressure sensor. Have a mechanic check it.

if you ran out of oil and you now can hear knocking sound comming from the engine then it time to get it checked by a mechanic

DTC P0521: Engine Oil Pressure (EOP) Sensor Performance

The engine oil pressure (EOP) sensor changes voltage based on the engine oil pressure. The EOP sensor is a 3-wire sensor comprising of the signal circuit, the low reference circuit and the 5-volt reference circuit. The engine control module (ECM) supplies 5 volts to the EOP sensor via the 5-volt reference circuit and provides ground via the EOP low reference circuit. The ECM monitors the signal circuit of the EOP sensor to determine the EOP sensor voltage is within the normal operating range of approximately 1-4 volts. When the engine oil pressure is high, the EOP sensor voltage is high and the ECM senses a high signal voltage. When the engine oil pressure is low, the EOP sensor voltage is low and the ECM senses a low signal voltage. The ECM sends the EOP information to the instrument panel cluster (IPC) via GMLAN serial data message.

Conditions for Setting the DTC
P0521
The ECM detects that the difference between the predicted oil pressure and the actual oil pressure is either less than 47 kPa (6.8 psi) or greater than 50 kPa (7.3 psi).

Your best bet ,take it to a qualified repair shop that has the proper diagnostic testing equipment to diagnose this.

I believe the sensor in the pan is for the low oil level sensor. The oil pressure sensor is at the back of the engine, by the intake manifold, towards the passenger side.

The oil pressure switch relays the oil pressure in the engine to the instrument cluster. The switch will illuminate the OIL PRESSURE light if the oil pressure drops below 2psi (13 pa). The switch is usually located on the side of the engine, under the intake manifold on the 2.2L engine and on the side of the intake camshaft housing on the 2.3L/2.4L engine.




Fig. 1: The oil pressure switch is located on the engine block under the intake manifold and is accessible from underneath the vehicle-2.2L engine



Fig. 2: Oil pressure switch location-2.3L/2.4L engine


Other, the low oil level switch activates the OIL light in the instrument cluster when the oil level in the pan goes below a certain level. The switch is mounted on the oil pan.


Hope this helped (remember rated this post).

This is probably a faulty fuel pressure regulator. You can rent a tool at most auto part stores that connects to the fuel rail to show you the pressure level. If it is low (less than @40 PSI) or if it fluctuates very much, replace the regulator. It is also a good idea to replace the fuel filter, as it can clog and prevent adequate fuel supply from reaching the engine. You may want to replace the filter first, as it is usually cheaper.

coolant leak may be intake commend on Chevy truck,,mite want to try locus oil treatment,,

ur oil pump may be failin-there r sensors everywhere on new cars-keepin u from starting as safety measure-computer systems r complex n things dont always show on 1 scan-they kinda hav the mindset of a pc

Hi! The problem you are outlining is very similar to the Rover V8 (Buick engine). We Brit's are used to the low oil pressure when warm. I presume a complete oil change engine flushed with new replacement filter has been carried out? Maybe a top quality synthetic oil with additive may help. You may take it a little further and replace the oil pump with an after market performance up rated one. If you really are worried about low oil pressure damage whilst in low rev's try Molybnenum Disulphide an oil additive which really reduces friction metal to metal wear particulary in the situation you are describing.
That's the best I can suggest at this moment.
Good Luck! and Happy New Year!
Paul 'W'
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