What is knock and how do you know if you have it?

[AbsoluteGTR]

Alright, well some kid test drove my car a few days ago and he said that my car is knocking. My car is fairly slow...not as fast as where it should be. At first I thought it was clutch slippage but this kid (has a 90 gst) said my car was knocking. I have done ALOT of research but havent really found what I am looking for. The problem with it is the car does not pull hard at all (boost is at ~15psi). So my questions are:

1. What is "phantom knock"?
2. How do I know if I am suffering from knock?
3. How do you even get knock if you dont have any significant modifications to your car?
4. How can I get rid of my knock issue (w/o having to get a logger, etc)

Also my mods are open air element, MBC (@15psi) and running downpipe...but here is the thing, I read a post in which that person suffered from knock due to their 3-inch exhaust, so they put back on their stock exhaust and the knock went away. Could this be my problem, since I am running just a downpipe? Would resetting the ECu work?

I have researched and read my eyes sore, but cant really find any relevant info.

Thanks in advance!

[Blackcrow64]

http://www.automotiveforums.com/vbul...d.php?t=164870

Courtesy of our nice organized Tech section.


And Kevin for writing it. lol

[AbsoluteGTR]

WOW, kevin is the man....lol

BTW, thanks brian, didnt think of even searching in the tech section. I think that was actually the first time I have ever been in there.

There was one part that I did not get though: (This is where he was explaining what we can do to help eliminate knock - it was the first bulleted item)

-Reduce the temperature of the intake air. Cold air intake. Larger more efficient intercoolers. More efficient turbos. Lower pressure drop of IC and piping, so we dont have to make an extra 2-3 psi just to get X amount of boost at the manifold. We can also dump in more fuel, which acts as a coolant (though water and alcohol are 6-7 times better at absorbing heat, think water injection) to lower the temp of the mixture.

What does he mean by this (the part above in bold)?

[Blackcrow64]

Ok, lets say you have you boost controller set to 20psi... Well, after the charge air goes through the intercooler it can lose pressure due to too large of volume to fill and it can drop to say 17 or 18psi instead.

That being said. 17 or 18psi is gonna be considerably colder than 20psi because your not packing as much air molocoules (spelling?) together. See, your charge air is gonna be the temperature of 20psi but only cooled as much as the intercooler would cool 20psi but you will also loose a few lbs of boost while it goes through there too. Now lets say you set your boost controller to 16psi and are able to run the charge air through the whole system without losing any boost pressure at all. The intercooler will cool that 16psi without a pressure drop a lot cooler than it could the same 20psi with a pressure drop...

Does that make sense?... I hope I didn't make it more confusing. lol

[AbsoluteGTR]

Originally Posted by Blackcrow64

Does that make sense?... I hope I didn't make it more confusing. lol

WTF???? Dude I am so lost...J/P I got you loud and clear, lol.

Well I guess when I get the chance I will clean my intercooler (side mount - stock) probably never ever cleaned. Hopefully this will help some.....

1. What do you think about the lack of exhaust "theory"? (Since I am running just a downpipe).

2. If you can think of other measures I can take to eliminate knock or atleast reduce it, please say!

3. Also, is their anyway I can test the knock sensor, without using an osciliscope (sp?)?

4. And will a defective/old 02 sensor contribute to my knock problem?

[Blackcrow64]

A bad o2 sensor can give you bad knock. It will think it needs less fuel maybe and do exactly what it needs it to do. Remember, an ECU is only as smart as the sensors connected to it...

Tuning and proper readings is the biggest keys to eliminating knock. Each car is gonna be different in this.

[AbsoluteGTR]

Originally Posted by Blackcrow64

A bad o2 sensor can give you bad knock. It will think it needs less fuel maybe and do exactly what it needs it to do. Remember, an ECU is only as smart as the sensors connected to it...

Tuning and proper readings is the biggest keys to eliminating knock. Each car is gonna be different in this.

Hmmmmm. makes me think....

If the 02 sensor was bad and was "thinking" that the engine needs less fuel then that would be grounds for knock (because it would get real hot); but the thing is, I go through a tank of gas so fast, and if excess gas is being burnt then I wouldnt knock (because gas is a cooling agent), would I?

Maybe my knock sensor went out?

Hope I didnt confuse you with all my blabbering, lol!

[Blackcrow64]

No, you didn't lose me. You are correct in your thinking. But if yout O2 sensor is on the blitz and ready to die it could just have some really screwed up tuning in its mind.

[AbsoluteGTR]

Originally Posted by Blackcrow64

No, you didn't lose me. You are correct in your thinking. But if yout O2 sensor is on the blitz and ready to die it could just have some really screwed up tuning in its mind.

Right, guess I might have to change it out. Ill try testing it with my ammeter first...sucks they are so expensive

What do you think about the whole no exhaust thing on my car?

[Blackcrow64]

Are you just running an open DP? Either way, it shouldn't matter. The only things within the exhaust that matter are the o2 sensors. Running an open DP will actually give it less restriction and should make it run better if you can stand it being that loud. lol

[AbsoluteGTR]

Yea the exhaust ends right below the center console. Not my choice, the previous owner decide to hack at it. It is loud as hell, and would be pretty happy with a stock exhaust.

[Blackcrow64]

Just put the rest of the 3" on. Stock exhausts are way too restrictive.

[gthompson97]

What octane fuel are you running? That can also cause knock if you're running too low of an octane rating.

Do you have e85 where you're from? Try putting in a 1/2 tank of e85 and 1/2 premium. That should bring the octane rating up to around ~97-102 I believe. It should make the knock go away for awhile (at least until you get it sold, or go through the tank of gas)

[AbsoluteGTR]

I run 91 octane. You cant really find anything higher than 91 where I live. Sometimes 93. I have never seen e85 for sale anywhere but I will keep my eyes open for it.

Should I try those octane boosters? How about the Xylol (sp) stuff you find in the paint store? Will that work?

[AbsoluteGTR]

Alright, I just realized that I have a laptop, lol. I am pretty sure I can my laptop to perform my logs right?

So will my laptop work?
Where can I get the software from?
Where can I get the cable from?

So all I need are these three pieces of hardware right so I can log, right?