1996 GMC Jimmy Oil Problems

[Chris_0908]

Here's some info on the truck first off. I have a 1996 GMC Jimmy with the standard 4.3 Vortec with 175,000 miles on it. Full Accel Ignition (Distributer, Wires, Plugs and Coil), Flowmaster 40, Side piped, K&N cold air intake with a JET Mass Air Flow Sensor. Running Mobil 1 and a K&N Oil Filter HP-2001 since 75,000 and I'm running with 15W-30, Jasper Transmission and Transfer case with a shift kit, I don't beat on her or drive her hard either and keep her maintained properly.

Enough about what's done here's the problem. About 2 days ago I changed the oil (every 5,000 miles like clockwork cause of the amount of highway miles I do), and ever since I changed it she's lost ALOT of oil pressure. When in park she would hold a strong 25 PSI now she's barly holding 20 PSI, in Drive or Reverse she's would stay at 20 PSI at and idol I'm lucky if she stays at 10 PSI now and when I'm moving she would hold a strong 40 PSI and now I'm lucky if she holds 20 PSI. When you first start her up from sitting (cold start) she hold's pressure like no tomorrow, but when she gets warm that's where the change comes into play. Well today while she was cold I put a container of the Engine Cleaner in and ran the engine from a dead cold for 15 minutes (like the container said) put a fresh K&N Oil Filter on and replaced all 4.5 quarts of oil in her. I had the windows down today and from a dead stop to about 2,000 RPM I heard a loud noise in the motor and it goes way when the pressure builds up from 10 PSI to a peak of 40 PSI and then back down to 20 PSI. I screened the used oil before I brought it to Autozone to get rid of it and I saw no sludge, no metal flakes nothing and I was running it though a painters screen. I'm thinking it's the Oil Pump or the Oil Pump Screen but I saw nothing in the oil, and I know it's not the Rear Main Seal because I lost no oil. If anyone has any information that I could use to get her back up and running please help.

Chris

[taillight]

Try a different guage just to make sure it is not just a bad guage. Then oil pump.