00 Chevy S-10 2.2L low oil pressure

00 Chevy S-10 2.2L
There are a few things that I need some feedback on....

1). I rebuilt this engine about 2 - 3 months ago for a friend it runs fine but has a light knock and today I got it back to put new hinge pins and fix the door jam where the striker is suppose to be and I heard this knock (very light), it had this low knock before, which goes away at higher rpms (around 1500) and I also noticed the oil pressure was very low (between 15-20 psi) so I think the knock is just caused by low oil pressure. When I rebuilt the engine I did not replace the Oil Pump - which I know I should have.
Do you guys think this is just a bad/weak Oil Pump or could there be something that I did wrong in the rebuild process that could have caused this, I honostly think it's just the pump this was the first overhaul I have ever done tho and want to get some other opinions. I mean it's not a bad knock or anything but very slight.

2). The FUEL GUAGE bounces around like crazy.

3). The Instrument Cluster Lights don't work.

Joe

While you should probably have changed the oil pump its not as necessary as you think. Oil pumps pump oil in VOLUME not pressure. The pressure is created by he restrictions the oil occurs as it flows through the engine, ie the main and rod bearings mostly. If you have to much clearance in these areas you will not have any or little oil pressure. The knocking you hear could be caused by by wrist pin or a cracked or broken piston skirt. But both of those should get louder when you rev the motor up. My oil pressure in my 2000 S-10 2.2 is only 20 at idle (Which is ok) up to 40-60 while driving. Your motor only needs about 10 psi for every thousand rpm's your motor is turning any way. More is really a waste. If you had a problem with the mains or rod bearings your oil pressure would be 0 at idle.

abadrs - thanks for the info.

What do you think the knocking could be caused by?