spark knock or not ??

[Spee-d3]

Too much of a puzzler for my brain so thought I'd solicit some real help to try and put this annoyance to rest: While driving on the freeway in 6th gear at 70-80 mph in 90-95 degree weather I get this "rattle" sound that, to me , sounds just like spark knock. Whats weird about it and what has me totally confused is that it is present only between roughly 2500-3500 rpm while under light throttle load and its also there intermittently if I take the car out of gear or clutch-in and coast (at freeway speeds) under zero throttle. There is never any rattle under full throttle acceleration or in cooler (< 90 degree) weather. I've looked around under the hood and can't find anything loose that might be responsible for the rattle.
Your thoughts ?
Solve this and the beers on me (fedex'd to your door of course!)

 

[Spee-d3]

Oh, forgot to mention the performance mods that may or may not have something to do with the "rattle" situation: Cobb SRI, CS race-pipe/CB.

 

[Super Unique]

Those mods shouldn't be causing an issue of that sort. Spark knock would trigger a timing pull, and if it still persisted would trigger a check engine light. Also spark kock would be there during throttle loads. it definitely wouldn't spark knock while coasting. Are you getting any lights or codes thrown. if so what?

 

[Spee-d3]

No codes whatsoever. I'm inclined to think it is not spark knock simply because of when it is occurring , but it sounds so much like that I thought I'd better get some other opinions. This is my first turbo car (I 've had NA and supercharged performance cars and know what knock sounds like in them) so I'm in the upslope of the learning curve here.
Thanks for your input !

 

[LBV]

Also spark kock would be there during throttle loads. it definitely wouldn't spark knock while coasting.

As odd as it may seem, that's not true on this engine.

I've got an Aeroforce scan gauge hooked up with the warning set to go off when the knock retard hits 4 and it would usually go off after a hard charge onto the highway and THEN when I got back off of the gas (ie. no load) is when it would light up.

I thought it really odd but it's happened several times when I was on the stock plugs ... went to a 1-step colder plug and I rarely get it now.

To the op, if u can get someone with a dashhawk or other scan gauge that monitors knock retard that's really the only way to tell for sure.

 

[Betelgeuse]

Yeah you need a scan guage of some sort. At this point you can't rule anything out. I'd recommend a dashhawk also - great investment you'll always use.

 

[Spee-d3]

LBV, interesting info. What plugs are you using ?
Betelgeuse, I will look into getting a dashhawk or similar monitor.

Thanks to both !

 

[dread]

I have seen people get knock retard under the circumstances you describe, you definately need a dash hawk to be sure.

 

[Super Unique]

so your telling me that the disi engine gets spark knock at idle? That's the weirdest thing I have ever heard.

You have personally witnessed this? Spark knock occurs under load when the flame front of the fuel accelerates uncontrolled due to volatile gasoline.

A noise while idling, engine out of gear and coasting wouldn't be spark knock.

 

[LBV]

Not sure who you're directing that question to Super? I haven't at idle.

For the colder plugs go with Denso ITV22 or HKS 50003-M35LF - the HKS's are damn pricey though ... both come already pre-gapped to .030".