99vortec

Hello! First I’d like to say that I’m new here and not sure if I’m in the correct place to be asking this or not, but I am in need of serious help with this engine... The truck is a 1999 LS silverado 1500 with a 5.3L vortec v8 lm7 in it. 265K miles. When I first got the truck this wasn’t an issue it just progressively got worse and worse until it just did it fully 24/7. I know this is a very common issue with these engines, but the symptoms I’ve been having are not the same as what Ive been seeing other people having. The truck started having a low oil pressure problem, where it would be fine when cold full around 25-30 psi, then as it warmed up / as I drove it, the pressure would slowly drop until 0psi, sometimes this wouldn’t happen till after driving 50+ miles, sometimes it would happen in 10 miles. Now after replacing the pump it does it in literally 1 mile. After it would drop to 0psi the lifter chatter/tap/knock (whatever you want to call it) would finally start up. I would stop the truck kill the engine then restart it. Most of the time after id restart the engine, the pressure would rebuild back up (lifter tap would go away) and I’d go for a mile or two, and then the whole process would just repeat itself. Make a long story a bit shorter... I ended up replacing the oil pump, with a mellings 295 pump, cleaned out as much gunk as I could, got the oil pan nice and squeaky clean... The truck did fine for a couple hundred miles, had really good oil pressure. it did lose all oil pressure entirely on my first test drive but it never had a lifter tap or made any noise when that happened I just pulled over killed it, started it back up and bam it had normal oil pressure.... After that happened, the truck did fine for a couple hundred miles, then out of nowhere it would just randomly start ticking even when it had OK oil pressure 15-25 psi. Prior to replacing the pump when the engine was cold it wouldn’t even build up oil pressure right after starting, usually took like 10 seconds + of it running for it too build pressure. And it would only build up to about 25psi and it stayed there even when warm. Now after the oil pump replacement, when the engine is cold the oil pressure will build immediately and be at around 60 psi, then as it warms up it slowly drops to 40, I’ll get out onto the road and as I barely make my way down the road, it slowly drops until it gets down towards 5-10psi and then the lifter tap will start up, doesn’t usually drop fully down to 0 like it did prior to the oil pump replacement. It usually atleast has a couple psi, but that ain’t enough obviously lol cause it’s ticking. When it does this, I have no choice but to pull over, kill the engine, start it back up, and it builds back a little bit of pressure. But it still has the lifter tap it doesn’t go away like it would before “sometimes”.... And it’s bad, I can definitely feel a power loss, also can notice a change in the way the engine sounds other than ticking, like a ****** in the timing or something? I know it’s NOT good and the ticking means there’s no oil getting to the head, so please save the lecture, please... I’m just at a loss as to why this would still be happening after replacing the pump? The pump doesn’t do what it did before I replaced it, which was, it would fail to build pressure after starting the truck when cold, that’s what made me think the pump was failing so I replaced it, and the new pump DID fix that issue... lol but that’s it... so I know it can’t be the pump right? I mean it’s literally brand new... I also tried to make sure the o ring wasn’t pinched when re-installing the pump... I really just need some good insight on this issue from someone that knows these engines well, this is killing me! This is my only vehicle I need to get this figured out ASAP. I did all the work myself, 23 year old guy, grew up working on bikes then transferred over into cars/trucks, not an expert by any means but I’m no dummy that’s forsure hahahah. Any help is appreciated! & The truck is a great truck, it’s an all around clean truck, the last owner definitely took care of it, so it’s not like it’s a big ass pos. Well kinda I guess lol..