I posted a while back about my truck having no oil pressure at idle. I changed the oil filter, the oil, and the oil pressure regulator valve. The problem stopped. Now 2 weeks later it has come back. No oil pressure at idle it finally struggles and pulls pressure with a little bit more RPM's and then pressure is way up around 80 or 90. Even after it warms up pressure stays the same. When it's around 80 and you let it idle it only takes about 3 secs and it's back at 0. any body have any help. Is there away to test the oil pump. It does have a mech guade on it.

 

From DodgeRam.org:

1999 ISB engine changes (begins July 1998)

• Diesel towing capacity has been increased
• To reduce oil pressure during a cold start, excess oil from the pressure regulator is now routed to the sump instead of the lub pump inlet.
• A new turbo charger wastegate mount is located on the compressor cover. As before, the wastegate dumps boost at 20 psi.
• The thermostat is redesigned for increased reliability.
• The fuel injection pump bracked has been strengthened for improved durability; it is now cast instead of stamped

Assuming this problem is an all-of-the-sudden situation, I would still be looking hard at the pressure regulator, more importantly that bypass portion. Other than the regulator, the other side of the equation for oil pressure is rod and main bearings. Assuming those are ok, I'd check your oil pickup for any restriction, but I'm putting my money on that bypass sticking open. Just another guy's opinion...

 

now wich one is the bypass b/c i changed the plunger and spring that goes in the top and to the right of the oilfilter housing. Thats when it got better for a while and the got worse.