2003 Impala engine knock

Hey Everyone, here is my latest problem with my 2003 Chevrolet Impala 3.4 engine...engine started knocking and running rough on sunday...i borrowed a autozone code reader and po401 came up...i cleaned the EGR valve but knocking did not go away...on someones advise i pulled one spark plug at a time and when i pulled the middle (front of engine) plug the knocking stopped, i put it back on and the knocking started again..can someone please give me some advise as to what might be wrong http://www.automotiveforums.com/vbulletin/images/icons/icon5.gif...thanks in advance...bobbyboy-g...

Moving this to the Impala forum. This Chevrolet Classics forum isn't the proper place for this thread.

Could be something broken inside the engine.Here is an easy way to find it it,use a very long screwdriver and put the handle near you ear.Point it near where the noise is coming from

Hey Fred, thanks for replying, i dont think anything is broken inside because when i pulled the plug wire the noise stops..out of curiosity if i do what you recommend would it reveal if something is loose or broken inside...another forum i went to says it could be valves sticking or rockers loose...i do know i need to take off the valve covers, but i was hoping someone had this same problem and i could try their fix first..http://www.automotiveforums.com/vbulletin/images/icons/icon6.gif bobbyboy-g

I would pull that spark plug and put in a new one. You might also try getting the plug wires changed. It is possible that they are arcing to ground or to each other.
A valve or rocker arm knock would not stop just because you pulled one plug wire.

Hey Iflylow, i changed the plugs and the wires on sunday and it did not stop the knock...i started the car a few hours ago and it seems to make a rat a tat rat a tat sound ending with a thump sound....it is coming from the engine just under the intake manifold area..i pulled the spark plug wire again and the knocking stops, it seems to actually run better without that wire on...when i put it back on car knocks and runs rough...thanks for replying...bobbyboy-g

Maybe a stupid question, but are you sure you got all the wires back on to the correct plugs?

Yes, the wires were put back in the original places...i am going to pull off the front valve cover to see if i can see any damage...thanks for taking time to reply...bobbyboy-g

Your piston pin or connecting rod bearing may be going on the one your pulling the plug to.

I'll vote for a rod bearing.

When you pull the spark from the bad cylinder, the piston and rod just get pulled around by the crank, so there is no change in direction as when the spark causes the piston to push on the crank.

Expect it to get worse before it gets better.

It's interesting that you got codes, so it's possible that you burned a piston/ring set and the piston is now rocking in the bore -- if you remove the oil fill cap, you may be able to hear and feel compression in the crankcase -- that would certainly indicate a bad piston. Pulling the spark from one cylinder might cause EGR codes, but I don't know for sure.