Not your normal knock issues Please Help

[DJ23GSX]

What could possibly cause knock only when the engine is cold and then go away once the engine is hot??
My issue is i get up to 43 counts of knock at 2k rpms when the engin is cold. The knock is there only over 20% throttle and goes away when i let off the gas for a second and then get back on it. If i stay on the throttle over 20% the knock is there all the way through the rpm band until i shift. It doesn't matter how much fuel I add or take away with the safc either. It goes away completely when the car is hot or after a few wot pulls. I have 0 knock at wot at 20psi but this low rpm cold knock makes it a rough ride. How can i be sure if this is real knock? Only sometimes my timing gets pulled because of it. So far i have tried 2 different 2g maf's checked the ecu caps boost leak test, compression test(162 165 170 165) and new spark plug's. My motor only has 5k miles on it since a rebuild where everything internal was replaced with brand new oem stuff so its not lifter tick. I am pretty sure my o2 sensor is dead but could this cause all this crazy knock? I also think my iac is shot but would that have anything to do with this? I have an o2 sensor an iac and a brand new knock sensor that are waiting to be installed are there any other things i could check or replace while i am doing those things? I am on the verge of selling this car because of this issue so any help to get me going in the right direction will be much appreciated.

 

[sbiggi]

Sounds like you have noisey lifters and once the oil heats up and thins out they stop making noise.

Either that or something is loose on the engine, and when it heats up and expands its not loose and making the noise anymore.

The knock sensor is just a microphone, it will pick up all kinds of noise, and if its in the right hz range the ecu will think its knock.

 

[DJ23GSX]

Sounds like you have noisey lifters and once the oil heats up and thins out they stop making noise.

Thats exactly what I thougt but they were replaced with brand new ones 5k miles ago. I have listened to the engine at idle when its cold and you can't hear anything. If it weren't for the 3" exhaust you wouldn't even hear it idleing. My last DSM had very noisy lifters but no knock. It makes no sense to me that its only there when the engine is cold and goes away when its hot even though i don't touch anything tuning wise. I also had a thought that maybe when they put the knock sensor back in after the rebuild they tightened it too much and when the block heats up the hole for the knock sensor expands making it read correctly. Thanks for your reply.


There is one thing i forgot to mention. The knock doesn't start immediatly after starting the car it takes a few minutes of driving before it starts.

 

[quickplymouth]

Did you figure it out? My car knocks at idle when cold then runs like a champ when warm. The noise goes away once I hit boost??

 

[T9S1i]

I think it could be one of a few problems.....
1. Knock sensor bad, or in the wrong hole, it needs to be in the lower hole, not the one right by the intake manifold

2. at low rpm, off bost you have a LOT of timing.... if you are seeing more airflow there then you are just getting knock. Check out your logger when this happens and see how much timing you are getting. If you have a 2g maf, ported this, ported that, and see boost real low your ecu might not be used to it and give you too much timing down low for the air you are flowing and its real knock...

3. Car isnt warm enough yet, oil hasnt expanded and whatnot (see above)

Im having problems with these same symptoms... when im in a gear too high for what i should be in (ie 5th instead of 3rd or so) and i floor it or even half throttle between 2-3k i get knock... Im pretty sure its just the amount of timing that our cars get right there...

hope this helps

danny

 

[quickplymouth]

Makes sense. My PDA was stolen so I can't log it, but I will check the timming with a gun this weekend. Thanks

 

[DJ23GSX]

I think it could be one of a few problems.....
1. Knock sensor bad, or in the wrong hole, it needs to be in the lower hole, not the one right by the intake manifold

2. at low rpm, off bost you have a LOT of timing.... if you are seeing more airflow there then you are just getting knock. Check out your logger when this happens and see how much timing you are getting. If you have a 2g maf, ported this, ported that, and see boost real low your ecu might not be used to it and give you too much timing down low for the air you are flowing and its real knock...

3. Car isnt warm enough yet, oil hasnt expanded and whatnot (see above)

Im having problems with these same symptoms... when im in a gear too high for what i should be in (ie 5th instead of 3rd or so) and i floor it or even half throttle between 2-3k i get knock... Im pretty sure its just the amount of timing that our cars get right there...

hope this helps

danny

I will definatly check out your second suggestion. How much timing is too much at such low rpm's?

**UPDATE**
I went out this morning and did some low rpm logging and my timing off boost is anywhere from 22* all the way up to 35* then then knock starts and timing gets yanked down to like 8-12* I didn't get to change the knock sensor yet but i plan on doing that in the next week so i will post the results if any one is interested.
Thanks