Hi, my grand cherokee 08 3.7 was rebuild motor, so i put the motor in the car, all connect and when is start is all ok, but when is warm idle the oil pressure is the 9 psi (cold 20psi), i change the oil filter,, change oil pump, change OP switch, checked leaks, i put 5w-20 oil motorcraft that means ? idont know what i do more D:

 

Hi, Eddy. Welcome to the forum!

How are you checking the oil pressure? With a mechanical gauge or an electronic gauge? If it's electronic, it could have a bad pressure sending unit. It's best to double check with a mechanical gauge. You can get a basic mechanical guage for under twenty bucks at any auto parts store. I picked up a Bosch for 17 bucks a few years ago. No need to mount it anywhere, just connect it in place of your electronic sender, fire up the engine, and see what you get. It only takes a few minutes to put it in place of the sending unit, and a few minutes to swap it back.

Something like this: https://www.pepboys.com/bosch-style-...628?quantity=1

 

Hi, BlueRidgeMark i checked the OP with a mechanical gauge and the pressure always is 10 psi (low idle RPM), we are checked all components, because we rebuild this engine, but the heads we send to machine shop, 3 days ago we took care of the camshafts and we saw that they are scratched, determining that there it loses pressure, but how or why were they scratched if the oil gauge had not started?

 

Sounds like maybe you didn't have a good assembly lube on the cam bearings, or some dirt got in there.

Cam bearings are famous for being the source of low oil pressure.

 

Wait! Don't the cams in the 3.7 run directly on the aluminum? Without a good assembly lube before oil pressure comes up could wipe out the aluminum bearings. Not good!