Lifter noise at cold start up

Hello all,
This is a continuation of many earlier posts. I have a loud lifter noise when the engine is started cold. More than one lifter, many are tapping. So many, that the engine is miss-firing and sending a error code to the computer, (flashing SEL light). After 3-4 minutes it smooths out and the tapping is gone, in fact the engine sounds perfect, (except for an uneven idle-earlier post). I replaced the UIM and gasket, the LIM gasket. put seafoam in the oil and drove for 2 days and replaced the oil w/AC filter. Still it hammers away. The pressure gauge reads about 50psi when cold, so there is certainly some pressure in the system, lifters dont make noise when the pressure falls as low as 10psi. If it were just one lifter then I might think different, but this is many. When I removed the LIM there was no antifreeze in the area and no foam, or looks of any water. The engine does leak oil but cant find the location of the leak. I need some ideas here, I will eventually bend the push rods.

thx R

Was this an AC Delo PF47 oil filter? Try replacing the oil filter again but use a better quality one. WIX, Purolator, Mobil, K&N, Baldwin, etc. Sometimes when you get coolant contamination after UIM or LIM gasket issues you have to drain the oil again or more than once after the repair job. The residual coolant damages the cheap rubber anti-drainback valve in the AC Delco oil filter which is now made by Champion Labs for GM.

I did the Zmax treatment for engine and transmission to my 99 after it hydrolocked and I had to replace the upper intake manifold. Running nice and smooth now.

I used an AC Delco.
Even if the oil is draining back into the pan it seems like it should not take 3-4 minutes to pump up the lifters.

I used an AC Delco.
Even if the oil is draining back into the pan it seems like it should not take 3-4 minutes to pump up the lifters.

If the anti-drainback valve goes bad due to a defect which is common with the AC Delco PF47 or by coolant contamination it sure will take that long. It is up to you to try a possible simple $5 fix. We can only suggest based our learned experiences.

Ive been using the AC Delco PF47 because it seems to at least have a drainback valve unlike the cheapo crap from the 10 minute oil change places.
I will consider using a purolator or Wix in the future. Good heads up. Thanks

Update,,,The lifter noise seems to be gone, (fingers crossed), I replaced the oil filter with a Frame TG 3980, this is not the specd one for the engine but the interface is exactly the same only its a longer filter. Fit just fine. The MAP sensor went bad cause of the dexacool junk in the sensor. Anyways the probles seems to be gone for now.