Oil pressure is zero at idle
 

Hi,

My van is Chevy 98 Express 1500, 118,000 miles.

Today, I found oil pressure was zero when it was idle, but recovered
to normal level during driving.

I suspect either oil pressure sensor, or oil pump.

In case it is the oil pump, can I replace it without taking out the motor?

One more question.

My understanding is, when oil pressure is below trigger level, fuel pump should be off, to prevent an engine damage.

But, my engine was runing fine with this condition. (when idle)

Does this mean bad oil pressure sensor?, because one signal goes to the computer (still OK), while the other signal sent to the gauge? (wrong signal?)

Thanks
Eaton