Hey what's up guys, I've got a knocking problem on my hands and I'd like some advice. I just bought a 91' Firebird 3.1L yesterday and it came with a mild sounding engine knock. I'm no stranger to third gen's and this car makes number 7. When I cold start it I hear it knock very briefly (1 or 2 seconds) and then it goes away. Once it's up to normal operating temp it comes back and has a very consistant "beat" so to say. The previous owner said that his "friend" came to look at it and said it was a bad rod bearing... Normally I'd consider that and or a main bearing but the thing is, this car only has 60,821 miles on it. I bought the car off of the second owner of the car and he only had it for a year and a half. The first owner was an elderly woman and she kept EVERY single service record and registration recipt, including the original window sticker! The car sat un-driven for about a year up until 2 months ago. I'm going to be replacing all of the spark plugs, wires, distributor cap, oil change, differential oil change, transmission & coolant, air filter, fuel filter. Would any of the items I just listed cause the engine to knock if they were faulty or worn out? The oil pressure gauge is reading about 80 when I'm on the freeway and goes down to 60ish when I'm at a stop. Any help would be appreciated!

 

Could be lifters. From what I know, rod knock is constant from startup to shut down. Lifters would be impacted by the amount of heat. If it's sat a while, perhaps the lifters have collapsed?

 

knock on startup would be due to one of 2 things
#1 oil pump losing prime
#2 anti drain back valve in the oil filter is not working

usually typical of a motor that has a knock sound for the first second or 2 of a cold start after its been sitting

how are u reading 80psi of oil presure i thought the stock gauges go only to 60 psi

i knwo in my car i had to install a aftermarket gauge cause when i built my new motor i shimmed the presure relief valve for more presure and my stock gauge will only read to 60 psi once oil presure goes over 60 psi the stock gauge just pins itself

and ive got 85 psi at idle and over 105 psi at redline cold
65 idle and 100 redline hot

when u say it knocks once it warms up is the knock constant with engine speed? anyway u can get a video clip or sound recording of it?

 

The stock oil pressure gauge on my 91' reads (20, 40, 80).

Yes, once the engine is warm and the knocking starts, it is constant with the engine speed and not erratic at all.

I'll make the video clip in the morning and post it right up.

 

Try a heavier oil, say 15W-40, and see if that dampens the knock. It may also be that the previous owner put 0W-10 in it. Push comes to shove can go to 20W-50 and see if it works out.

With your location it isn't going to ever see below 50 F temperatures on a cold start.

RBob.

 

reg dino 20-50 has kept mine going strong all these years.

Along with some duralube ever few years.
Stuff has proved it self to me just like on TV several tiems with different cars that should of ruined the engine but just like on TV it did its job.

Also run straight 30w oil in my T5

Never had a problem with either even with cold Ohio winters. I just let it warm up a few mins.

 

i always swore by castrol stright 50 wieght,but im actually trying something new in this motor, ive been using rottella 15-40 oil in it since breakin,so far so good

 

Thats good oil for a new motor, lots of detergents to keep them fresh and clean for life. Buick folks report engine staying like new inside.

But in a hi mile engine, you don't really want a hi detergent oil losening up junk.