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Does anyone know what the average oil pressure should be on a 3.1L after being warmed up, in gear, and idling?   My '90 had a bad oil pressure switch in it when I bought it and always read 0 lbs.  I replaced the switch a few months ago, and once the car is warmed up, I can be sitting at a stop light in drive and the pressure is only about 5-10lbs.  As soon as I hit the gas the pressure jumps to a normal 40-50lbs.  I know 5lbs. is way too low for a 3.1L, but it still runs like a top.  Any ideas? I flushed the motor out with a little of that Motor Flush/Kerosene stuff and have been running 10W40 in it.  Do I need a new oil pump?

I've seen that a lot and I currently have a 3.1mpfi with the very same situation.   Just drive it, it'll be all good.  Now, if you start hearing ticking/tapping/knocking is when you should worry.

I agree with GTU. I have an '88 GT with a '90 3.1L MPFI in it. Same thing. Warmed up at idle, 5-10 psi oil pressure. Touch the gas , jumps right to 40 psi. The oil pumps are gear driven so the more RPM's, the more pressure. My motor is only 2500 miles old. I would worry unless you hear noises as GTU said. GL.

That makes sense.  The only noise I hear from my car is a little valve chatter/lifter noise when I start it up when it is cold.  I hear chatter for a few seconds, then it disappears.  I don't think its a problem, so I'm not gonna worry about it.  I'm just glad I'm not the only one.  Thanks guys

The noise you probibly is GM's piston slap. Happens for the first couple seconds(up to like 2 minutes) then as the motor warms up it fills the void and no more noise.

Anyways... my old GT U used to get around ~20psi at idle and ~50 psi at 2K rpm. It's normal for the oil pressure to jump up with higher rpm. Good rule of thumb is that you should have at least 10psi oil pressure for every 1K RPM.

I seem to remember reading somewhere that GM had sent some kind of notice to the Chevy dealers about low oil pressure issues in the 2.8's/3.1's.

Alot of customers were complaining about perceived low oil pressure. GM said that in these engines 6-9 p.s.i. at idle was perfectly within spec. When my car is fully warmed up, I have around 3 bars on my digital cluster's oil pressure gauge. When I wind it out, the oil pressure goes up accordingly. I put a high volume oil pump in this 2.8 that we got from the junkyard just for extra insurance, since it already had 90,000 miles on it when we transplanted it.

(Scanman88GT @ Sep. 07 2008,12:04)QUOTEI put a high volume oil pump in this 2.8 that we got from the junkyard just for extra insurance, since it already had 90,000 miles on it when we transplanted it.
Those pumps need a deeper oil pan to help prevent pump starvation.   The upper end will have oil, but the chain and lower end will be left dry.  
One thing that I would only do for the oil pump is tack weld the pick up tube on the pump.