Engine knock

i have a 1990 bmw 318i and it has this terrible engine knock when the rpms are below 2000. what is it

Is this knock more like a hammer rapidly hitting a rock, or is it like a bunch of marbles rattling around in a tin can?

If it is the latter, then it may just be pre-ignition as a result of superheated carbon in the cylinder. On the other hand, if it is the classic “hammer” sound, this could be a connecting rod that is about to go through the side of the engine block.

If it is a true knock (i.e.–hammering sound), I strongly suggest that the OP not start the engine or drive the car before getting this properly diagnosed.

Are you using cheap gas or high octane gas?

I believe your car calls for high octane. Are you using high octane?

it sounded like a hammer hitting a rock till last night then the noise got so loud and i was driving home last night and it shut down. now the car wont even turn over. i know its not battery but thats as far as i got today.

i am not using high octane fuel

Have you checked the oil level?

Ed B.

plenty of oil

Is there too much oil?

If the engine won’t even turn over after extremely loud knocking noises, I think you got BIG problems, possibly failure of major parts (rod, lower end, who knows?). I don’t think it’s an octane-related problem.

1990? Loud knocking followed by suddenly shutting off then inability to turn over?

I’m afraid Texases may be right. I’m afraid the knocking was probably a critical bearing (probably a main crank bearing) knocking just before seizing.

Put the car in neutral (chock the wheels and put the parking brake on), remove the spark plugs, and see if you can turn the crank manually. If not, the engine is seized.