Yesterday my 2000 xj 4.0's oil pressure dropped to zero for a moment while at idle. This morning I started it and a nasty knocking sound came from the engine(could not pinpoint) and the oil pressue fluxed between 70 and 40 a few times. After it warmed up the pinging sound went away and the oil pressure stabilized.

A little background...I just had the cylinder head fixed along with all valves re-done last week. I have not had any issues with engine kncoking even after I changed the cylinder excpet for this morning. Do you guys think the oil pump is failing or to change the oil again will help with this. I know this is a loaded question, but I'm really at a loss with this thing.

 

Do you have access to a mechanical guage to check the oil pressure with?

How many miles on the engine? What weight oil?

 

Oil pressure has been verified with mechanical guage, I use 5w-30 and the engine has 113k on it.

 

It could be a clogged passage or a bad oil pump.

If it was me, I would run something like Sea Foam through the crank case to try and clean it up. An oil pump is pretty cheap but a PITA to replace.