Engine has a knocking sound.

Just to add to this one when you run those engines low on oil they usually will spin a rod bearing not make the top end click.If your low on oil they will click i would test it for a rod knock.Put the valve cover back on but when you do you will need to put a bead of silicone across both T joints.On each side of the cam gears where the front timing cover meets the head that outter edge put a nice bead of silcone there or you will have a oil leak.When you put the spark plug wires back dont intstall the wire hold downs.Now start the car up remove the number 1 spark plug wire is the noise still there or has it changed?Put number one wire back on then go to number 2 and do the same untill you have done all four.Let me know what you find.

Yes the sound changes. Pulled plugs. A lot of miles on them/ changed them.

If your pulling a spark plug wire off the plug while it's running and the noise changes you have a rod knock.

Not nessesarily, sound changes because cylinder isn't firing. I am a journeyman autobody technician. I'm car wise and I can tell u its coming from top end. The oil is dirty. The engine shut off because it ran low on oil, but new rod bearing were installed. Trans ran low on fluid, engine reved a bit high 6500-7000.thats when the knocking. I'm up close and the top end is making the sound. I added some new oil and it did quiet it down a bit but just for a few moments. Its not a deep low end noise. Almost, but little higher pitch top end. Lifters I think. I really appreciate an experienced auto mechanic not technician. School to start but when it comes to cars, mechanic means they can hear a noise and they'd be 98% correct with the answer.You can't beat the experienced old timer. Worked with a few(now I'm one)? I'm not putting u in that category, realized your header says tech, nothing personal if you're human. Any input is appreciated. Thanks

Iam factory trained saturn tech have worked for saturn for over 16yrs.When you pull the plug wire and the noise goes away that's the piston on down.I have seen wrist pins etc bad and that trick works great.What year make and model engine do you have?That would really help so I could better visualize what set up you have under the valve cover.

Ok, 1999 Saturn sl2,dual ohc, my mother bought it brand new. It has 57,000 original miles. I put the 7,000, it ran fine until that shop messed it up. I told him off(the manager) anything else.

I think u are spot on! Now the dyelamia

SATURNTECH9 is one of our best!

Please let us know what happens.

Cheers, Ken

Hi, I just wanted to express that I'm car-wise. Didn't mean anything towards him. Hope u understand. I learned antibody by experience not school. Its making different noises. I plug the hose between the air filter housing and valve cover and it quiets down, except when I give it gas then top end knocking and a noise lower end slap.

Does the engine have smooth power or is it misfiring? I would suggest removing all of the spark plugs and look for discolor in one of them. Also lets roll a compression gauge and look for a low reading to also help pin point the cylinder giving us trouble.

https://www.2carpros.com/articles/how-to-test-engine-compression

Please run this test and get back to us so we can continue helping you.

Cheers, Ken

If there is top end noise and lower end noise also then sounds like it's time for a different engine.have you checked the timing chain yet?