Guys, I am trying to diagnose a weird engine knock. I have spent many hours reading old threads and the only one I found that engine sounds like mine is BlackMacks thread where it turned out to be a bad spark plug.

Anyway I taped mine so you guys could let me know your thoughts. The knock only happens after engine is warm and is more noticeable at lower RPM's and ALWAYS knocks 2-3 times after ignition is turned off. It happens more during decel than when increasing revs.

Here is a link to to a recording of it:


Thanks in advance for your help!!

Steve

 

Not sure whether its pre detonation but, First question as always... Is 91 octane gas being used?

 

Yes 91 gas is being used. I am almost 100% sure it is not pre-detonation. Way to loud for that.

I did some more investigating on the possibility of bad plug or coil.

When I disconnect any of the coils on the front bank (radiator side) all I get is a miss but no knocking. When I disconnect any of the 3 coils on the back side (firewall) the knock becomes rythmick and very pronnounced. Not somewhat random like the first video.

Here is a video of me disconnecting a coil on the rear bank:

 

Bad pre-cat

 

Sounds pretty much identical to mine. I haven't put mine back together yet, but at least the rear precat is shot with all the material detached inside (about half of it had made its way into the main cat). I'll be taking the front one off to check it tomorrow.

 

Sounds like the begging of what I was having... then got worst...Ended up being a bad rear pre-cat. listen to the 2nd video, tell me if that the noise you hear when the ignition is off.

http://forums.maxima.org/5th-generat...oise-idle.html

Additionally, if you put your car up in the air, you may be able to better pin out the noise location. At first I thought mine was from the engine, but pinned it down the the pre-cat after lift