First we would need to know when this occurs. \012Asuming the oil level is at the full mark!. If the pressure goes up \012during acceleration and down at idle when engine is fully warmed up, \012then this is normal. An engine requires 10 psi of oil pressure per \0121,000 rpm ( ex. 20 psi at 2,000 rpm, 25 psi at 2,500 rpm, and so on ) \012. If the gauge is moving back and forth erratically at idle , i would\012 say the gauge is bad. If it drops to 0 while accelerating I would say \012your oil pump is bad. If from time to time it seems to work and other \012times it seems not to work, I would say the oil pressure sending unit for the gauge is bad. \012 \012 \012If the pump failed you would start to here a \012Knocking noise from the engine in a short period of time. Use the \012above scenario's to narrow down what it may be.