Oil presure uuup & dddoown???

Ok fresh 400 on level ground and constant rpm. About 2200 and 70mph. 60 lbs for several minutes next check a few seconds later 45lbs. Holds steady for a few seconds slowly back to 60. A minute later down to 45 then slowly back to 60. Using the old reliable Melling standard pump and pickup and new shaft with 1 quart of GMs breaking oil and a gallon of Rottla 15-45, Napa longer & slim filter to clear exhaust. 25 lbs at hot idle in gear 650 rpm. 1000 rpm 40 lbs. and climbing fast.  

If your oil pressure line is coming off of the oil filter housing check for a bad by pass spring in the housing.  

Yes the gauge feed is from the filter mount. I was just at two other Pontiac sites and found nothing except brand new filter mount that come with the spring, retainer & retainer screw. Price is $89.00 plus freight of course. If I have the GM part number there is some NOS stuff that may do it for this spring. I would bet that GM will not have this part available. My machinist though it could be the by-pass in the pump just having not setted and binding now and then. If anyone has the part number please let me know.  

Some times dirt can get in the pump and cause the check ball to not seat fully.  
professional hi-performance engine builder

Horsepower sells engines and torque wins races

Thanks PM8. Do you think it will evenually clear itself??  

Your welcome no it usually wont.  
professional hi-performance engine builder

Horsepower sells engines and torque wins races

Here is one by Kauffman that doesn't have the bypass. It's $55. Look about 3/4 down the page. I got one on my last rebuild, I like it alot.

http://www.krepower.com/KRE_aluminum_parts.htm