[LEM]

The oil pressure gauge seems to be pretty erratic, sometimes showing zero pressure other times showing middle of the normal range at the same engine RPM. This past Monday morning I started the car after it had been sitting for three days and the engine knocked (like it normally does immediately after I change the oil until it build up to normal presure-usually like two seconds or so). This time it kept knocking for about five seconds or so and I shut it down and checked the oil-it almost didn't register on the dipstick, but the oil level trouble light never came on.

I added a little over a quart of oil and the knock quit, but the oil pressure gauge is still erratic.

When the oil pressure sensor malfunctions what are the usual symptoms? Where is this sensor located? How can I measure the oil pressure to check the oil pressure gauge?

Thanks.