'96 Zetec 2.0 oil pressure...HELP!
Just rebuilt the 2.0L Zetec in my daughter's Mercury Mystique and have an oil pressure issue. When first started the oil pressure light would go out until the idle speed dropped down to around 1200rpm, then it would come on dimly at first and brighten as the rpm continued to drop. Installed a pressure gauge and found that at 12-1500rpm oil pressure was only about 10-12psi. Obviously it fell from there as rpm decreased.
During the rebuild the oil pump and relief valve were inspected and checked out just fine. No scoring or scratches, and there had been no previous issues with oil pressure prior to pulling the engine, so the original pump was cleaned and installed. The crank mic'd out great and was installed with all new main and rod bearings, so I'm confident this isn't a clearance issue in that area.
I've rebuilt more engines than I can remember over the years, but this is the first Zetec I've been into. (I can do pushrod V8s in my sleep!) Not being familiar with this engine design I can't help but wonder where I may have messed up. One thing that bugs me a bit is the plug for the relief valve. The book I'm using says to replace the o-ring on the plug but I'm sure there was no o-ring on it to start with, nor was there a replacement in the gasket kit. Of course, the same book also says that the valve is accessed on the outside of the pump housing, but this one is inside the confines of the oil pan.
Anyone have any ideas? I hate to have to drop the pan and pull the pump assembly off but I'm not seeing many options at this point.