Is this the sound of rod knock?? Infiniti m35

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I had this car for about 7k miles now has 99k. Every time the car is in gear drive or reverse and under a low load (feather foot tap on throttle) around 800-1000 rpm or so it knocks. The noise is greatly reduced in neutral or park. The car can go to full 6k RPM and no funny sounds. Also if I am in drive and hit the throttle a bit hard, won't hear the knock. It only occurs under a low load and low rpm.

I just changed the oil to Castrol 5w40 and has not changed the sound. I feel like the sound is louder when engine is cold and reduced as it gets hotter but still present. Has been doing this since I got car around 93k. See video below


https://youtu.be/H8Iq398wgS4
 
I didn't listen but flex plate in the trans? also motor mounts.

I have had noise issues with Nissan filters either nissan chinese ( terrible) or Mexican Gonher (defective design in ADBV)

Are you running a good large wix (57356) or Champ labs non ecore?
The Titan V8 filter will give you more ( maybe 1/3 more) surface area.
 
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Everything you describe points away from being rod knock, which will be more prominent under load and affected by viscosity so will typically be loudest hot and quietest cold.

Almost sounds like detonation/heavy spark knock based on your description but then I watched your video and it seems less likely. It could be piston slap.
 
Get a mechanics stethoscope and go around the engine when you hear the noise. This should help pin down the origin of the sound and then you can make some educated geusses/assumptions and go from there.
 
Originally Posted by OVERKILL
Everything you describe points away from being rod knock, which will be more prominent under load and affected by viscosity so will typically be loudest hot and quietest cold.

Almost sounds like detonation/heavy spark knock based on your description but then I watched your video and it seems less likely. It could be piston slap.



Keep on mind when I say under load I mean in GEAR only. Under load when it's in drive and going to 1500 rPM or more it's clean and no noise. Even take it to WOT and no funny noises. Only at LOW load when in gear. What's a piston slap and how to fix it? Rebuild? Spark plugs are new and always used 93 octane fuel
 
I was always under the impression that rod knock was constant whether the engine is in drive or neutral. As long as the engine is running, rod knock will be present although not as loud.

This seems like something else. Transmission?
 
Originally Posted by audia6
Originally Posted by OVERKILL
Everything you describe points away from being rod knock, which will be more prominent under load and affected by viscosity so will typically be loudest hot and quietest cold.

Almost sounds like detonation/heavy spark knock based on your description but then I watched your video and it seems less likely. It could be piston slap.



Keep on mind when I say under load I mean in GEAR only. Under load when it's in drive and going to 1500 rPM or more it's clean and no noise. Even take it to WOT and no funny noises. Only at LOW load when in gear. What's a piston slap and how to fix it? Rebuild? Spark plugs are new and always used 93 octane fuel


Yep, rod knock would get louder under increased load, which is contrary to what you indicated was taking place. it also gets louder as the oil heats, which you say is not the case, ergo, I don't think it is rod knock.

Piston slap is excessive piston-to-wall clearance that some engines were notorious for, like some GM LSx series engines in trucks. It doesn't appear to impact their lifespan, so if that's all it is, and you can live with it, you'll probably be fine.

I 2nd the recommendation to get a mechanic's stethoscope and see if you can pinpoint where it is coming from.
 
Check and watch your serpentine belt tensioner. If it is really bouncing, that can sound like rock knock , especially on an aluminum block engine. Common sound when bad on s saturns.
 
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Rod knock is most noticable when transitioning from rev-up loading to no load. Like neutral rev and fall around 2500 rpm.

Mains knock under load unless totally trashed.
 
First thing is to stop womping it up to 6 grand until you know what it is. You can perform a cylinder balance test, if it is a rod it will show up as soon as the offending rod has no pressure on it from firing. On old cars you could just short an ignition wire out one at a time but I wouldn't mess around with that on a ECM controlled engines you could smoke some parts so you need a decent scan tool.

Listen to the engines parts from front to rear including pulleys, and their related parts eg A/C compressor, PS pump, alternator, etc, bell housing, oil pan, valve covers until you find the spot the noise is loudest then investigate.
 
Like Trav said, you really should not womp the car like that. If that's an 04-08/09 I suspect the catalytic converter has an internal failure and what we are hearing is the honeycomb rattling around under idle low load.
 
I believe I read of a similar issue on some NIssan VQ35's where this type of knocking was a 'water hammer' noise of sorts from the fuel rail caused by fuel pressure/pulses. I'm not sure what the fix was..
 
Your not going to be able to diagnose a knock sitting in the sound insulated passenger compartment. You will need to get out of the car and open the hood and let us hear it then. Also move to the ground and listen under the car, and vary the speed slowly don't rev it crazy.
 
Originally Posted by OVERKILL


Yep, rod knock would get louder under increased load, which is contrary to what you indicated was taking place. it also gets louder as the oil heats, which you say is not the case, ergo, I don't think it is rod knock.

Piston slap is excessive piston-to-wall clearance that some engines were notorious for, like some GM LSx series engines in trucks. It doesn't appear to impact their lifespan, so if that's all it is, and you can live with it, you'll probably be fine.

I 2nd the recommendation to get a mechanic's stethoscope and see if you can pinpoint where it is coming from.

I think rod knock gets louder when coming off the load. Revving on the way up is not bad, then you let off gas and as engine RPM comes down, rod knock is well evident. When it gets really bad it knocks at idle constantly. In the OP's case, Id say flexplate or exhaust component.
 
The engine is still cold. Does it do it warm?

Certainly not rod knock. Almost sounds like piston slap or an exhaust leak.
 
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Originally Posted by Trav
First thing is to stop womping it up to 6 grand until you know what it is. You can perform a cylinder balance test, if it is a rod it will show up as soon as the offending rod has no pressure on it from firing. On old cars you could just short an ignition wire out one at a time but I wouldn't mess around with that on a ECM controlled engines you could smoke some parts so you need a decent scan tool.

Listen to the engines parts from front to rear including pulleys, and their related parts eg A/C compressor, PS pump, alternator, etc, bell housing, oil pan, valve covers until you find the spot the noise is loudest then investigate.


^^This. Man when I hear people put the pedal to the floor while in park or neutral it makes me cringe! That just can't be good for any engine.
 
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