Hello, I'm Chris.I will do my best to answer your question fast and accurate using the info you have provided. Thanks for visiting Just Answer.
You have ruled out the easy components that we hope are all thats wrong. You now need to do an actual oil pressure test with a PSI gauge hooked up to the engine. If you get the same results of low pressure then you have a oil pump failing or gunk buildup in the engine.
Chris; Thank You for the time you have spent so far on this ? I changed the oil pump this week even though I did not feel it nessasary as there is very little tolerance in that pump for wear. The new pump did nothing and cost a $100. As I wrote earlier I had the motor apart and while I had it in the machine shop, I had it mic'd and the bearings and crank,etc were in good shape. Had the entire motor steamed and degunked, a valve job, new timing chain and gears, new shaft to drive the oil pump, new sending unit,changed the dash cluster. The motor runs fine, it initially idles at 1100 rpm and the oil presure is normal, when transmission is engaged the rpms drop to 950 and the oil preasure gage flutters and drops to zero.When driving the preasure reuturns to normal.
My hopes in posting on this site is that a guy spots the exact symtoms and has repaired it to normal. I bought the car to resell so do not want to change every part on it.
If this added info helps let me know or if I should repost let me know. I am not abusing the site and will pay for the correct info. Than You again ED
Have you done an actual oil pressure test yet to see how low the pressure is getting, like I mentioned in my first response?