i have a 90 ls400 around 300k miles, i posted on here a while back about my engine making a knocking noise. Recently i noticed my PCV Valve hose was being sucked shut by the airflow because the rubber hose was too soft, after i replaced it with a stronger hose the knocking went completely away, does anyone know why?(i assume it’s pressure related lol)

but about 25 miles later i started hearing loud squeaks and knocks so i pulled over to check my fluids then drove another 15 miles home, It had small loss of power and knocks are coming from the front drivers side of the engine. I’m just trying to brainstorm right now while i can’t work on it

Here’s a video https://youtube.com/shorts/VRyBjjugae0?feature=share



Sounds like a bad timing belt pulley but that PCV was a part of the issue for sure

 

Take a video from under the hood, engine idling. Then rev the engine up and down several times.

 

here’s a video i took earlier: https://youtube.com/shorts/UQP74Xrzboo?feature=share
maybe i got torque specs wrong when i did the timing belt job but i’ve put a few thousand miles on it since then and it’s been running great

 

Have you carefully checked the serpentine belt?
One idea to check is to remove it from the engine and start it. Do you hear the same noise? If not, it simply means that the belt is related.

 

i started it without the serpentine belt and took a video of me revving it a little bit
https://youtube.com/shorts/lBwFAUALzA0?feature=share
At the end you can hear the squeaks i was talking about

 

That sounds a whole lot like rod knock, but the squeaking I'm not sure.

 

The squeaking and knock appeared at the same time so i’m hoping it’s timing related, i drove 65mph for about 15 mins to get it home and it only made noise when accelerating. if it was rod knock would it be able to go that fast for that long?

 

The knock sounds kinda "hollow" like it's under the cam covers. Noise on acceleration confuses the issue. It may not be engine bearings but a fubar piston and cylinder.

I'd take a length of heater hose; put one end of the hose at your ear and point the other end around the engine to find the approximate location of the noise origin. I'd poke around around the exhaust manifolds as well. A long shank screwdriver works too.

Engines will run for a surprisingly long time with "bad" knocking. I had an '82 Pontiac Bonneville with a 4.1L V6 and 120k miles. I bought it not running for $200; it threw a timing chain. When I got it back together, it ran great but it knocked like a diesel. I drove that car for another 120k trouble-free miles. The only reason I got rid of it was the vinyl roof started to peel off and it was more money than it was worth to fix.