Loud knocking noise...Need help fast

[squeak104]

I left from work tonight and I give it some gas and a few minutes later I noticed a loud knocking noise coming from the engine. So I pull off and make sure nothing majorly bad is happening. Blah blah, and I get home and it seems like the sound is coming from around the #4 cylinder, on the intake side. You can definately feel a difference in feeling on the valve cover from that area and somewhere else on the valve cover. So I took the valve cover off and everything in the valvetrain appears to be fine. The noise sounds like an exhaust leak but the vibrations from it are on the intake side. When I gave it some gas on the way home after checking it out, the boost would go to 15 then taper off to 10 even if I held the pedal the same. I don't know what the noise is. Any help would be appreciated. Thanks in advance.

 

[huafist]

Start the car, and pull the plug wires one at a time to see if the noise goes away. Start w/#4, and if it doesn't go away, plug it back in and go to #3. Repeat all the way to #1. If pulling the plug wire makes the noise go away, say hello to a spun rod bearing.

 

[squeak104]

Oh yeh I forgot to mention. The car runs completely fine as long as I don't get into boost. It idles and runs like normal. But when it boosts, if feels like it misses and it can't hold boost. I don't know if that helps or not but its more info.

 

[squeak104]

I pulled each spark plug wire and the noise stayed there through all of them. Any other advice?

 

[huafist]

I pulled each spark plug wire and the noise stayed there through all of them. Any other advice?

Drain the oil and check for metal flakes - you may have spit out a balance shaft bearing - how does your oil pressure look?

 

[squeak104]

I drained the oil and there aren't any metal flakes. Its still very clean. My oil pressure is normal at idle and when I'm driving.

 

[huafist]

Well, there's only so many things that can cause a scenario like this.

My next step would be to check the cam timing and make sure everything lines up (that you're not smacking a valve with a piston, although I doubt it if it runs fine @ idle). When you say it runs fine at idle, do you mean the noise isn't there or it just idles solidly?

If the timing is on, I'd bite the bullet and pull the oil pan, visually inspecting all the bearings.

 

[squeak104]

It idles solidly. No missing or jumping rpms or anything. I'll check the timing though when get a chance. It doesn't seem to me though that it would be timing since its running like normal as long as I don't boost but I'll check it anyway. I won't be able to check it till next weekend because I have to head back to school now. I'll talk to my teachers at school this week and keep you posted. Thanks for all your help.

 

[squeak104]

My teacher and friend that knows a lot think that it may be a partially blown headgasket. Nothing in the water jackets part, so it would just be leaking out compression. I'm gonna do a compression test when i go home on the weekend and post what I find.

 

[squeak104]

FOUND THE PROBLEM

I got my car in the shop today and we played around with it a little bit and eventually did pull the oil pan off. It did spin the #4 rod bearing. No metal shavings at all came out with the oil. All the shavings were at the bottom of the pan and didn't come out with the oil. Oh well, I have finanicial aid money so it's time for a rebuild. I guess 170,000 miles isn't too bad for it. Thanks for your help.