Somewhat of a newbie here! With a question about Knock..

[94TSiBeast]

So I have a 94 talon tsi. It has several mods done to it, and the stock boost gauge is wired up to read Knock. So every once in a while when I'm driving the stock boost gauge spikes (reading knock) and the car has like no power when this happens. Then it goes away after a min. This happens under normal driving conditions, and sometimes when I try and accelerate. When it happens I let off the gas because I'm sure its not good.. But my question is what is causing this to randomly happen? Some days it happens alot, other days it never happens, or may not happen for weeks at a time. .. So I'll list my mods so that maybe that will help. Also the car is an auto.

16g turbo
680cc injectors
ECU Chip tune
2g Maf
2.5 intercooler pipes/ Big front mount IC
Full 3in. exhaust
Tubular manifold
3in. o2 housing with open dump
255 Walbro pump

I'm probably forgetting somethings, but thats most of it. So if anyone has any insight on whats causing my issue please let me know!! Thanks.

 

[GofaST4life]

I have two mains questions that need answered here.

1. "ECU Chip Tune" - What tuning device/software is being used?
2. Do you have a wideband gauge? (one wasn't mentioned)


Your car feels like it loses power probably because its pulling timing once the knock is detected. Which is a normal and needed function.

 

[tmoney20g]

If it is not from tuning, then something is causing vibrations. Loose bolt, lose bracket, etc. It's what we call "phantom knock". Maybe reading thru a couple posts from here and there might help you track down some causes/fixes:

https://www.google.com/?gws_rd=ssl#q=phantom+knock+dsm

 

[94TSiBeast]

Sorry yes, I do have an AEM wideband hooked up. And I don't remember who the previous owner said the Chip was made by.. I might be able t find out. Is it possible that its reading phantom knock and not actually knocking but still pulling timing?

 

[briansmith]

If it is occurring during no boost it's most likely not knock. Sounds like you are experiencing a misfire. I would plug the plugs and inspect to pin point down the cylinder u are having trouble with. Then diagnose from there

 

[briansmith]

Knock is a pre detonating caused be hot lean cylinders being feed lower octane fuel unable to handle the conditions it's being introduced into

 

[94TSiBeast]

I'm thinking its not from tuning, mainly because its not a consistant thing, Its VERY random. And the AFR's on the wideband read normal when it happens...

I always run 93 octane

 

[tmoney20g]

Could also be an old knock sensor, they do wear out and become overly sensitive. If you look back there at it, and all the black goo has melted/oozed out, it is time for a new one. You also have to pay close attention to torquing it properly....which is kind of hard since there is no factory torque spec. You don't want it loose, obviously, but you can't wrench it on there either or it will be too sensitive. So hand snug then 1/4 turn with an adjustable wrench is suffice.

 

[94TSiBeast]

Ok thank you, is that something I can get from like autozone?

 

[curt-s]

Pay attention to the RPM range when this happens, as it may not be as random as you think. For me on a 1g ECU and KS, it always happened at specific RPMs (coinciding with various resonant frequencies of pretty much every damn suspension and body part), regardless of what throttle position, torque, or teflon washerin'.

Just curious if it's truly random or actually repeatable with some thought.

 

[94TSiBeast]

Its random in the fact that it doesnt happen consistantly. It happens some days and not others. So I can't just make it happen. Its not random in the fact that when it DOES happen its the same everytime. So I want to find out what makes this flare up one day and not another.. whats the variable.

This morning it was happening really bad, only thing that was different this morning than other mornings was that it was alot colder and we got alot of snow. But the car is kept in the garage. This morning it was worse than its ever been, the knock was the same in low RPMs and happns under normal acceleration. But it took alot longer for it to go away.

 

[bastarddsm]

That sounds 100% like phantom knock. I'd try a new sensor. If you can't replace it right now, you could unplug it. You'll get a check engine light, and in boost it will automatically assume 8 knock counts, and pull like 2-3 degrees. It's pretty safe like that if your not out beating the piss out of it. As it is right now with PK, it's prolly maxing it out at 43cts and pulling lots and lots of timing.

Your best bet is to pull the chip out and have someone with a burner read it and see whats on it. Then they can add in a phantom knock code which will help out a lot.

I'm part of the dsmecu.com forum, and there is probably someone there that can do it for you. There is also ds-map, and a dsm ecu yahoo group, all of which contain factory code modding enthusiests.

 

[bastarddsm]

If the ecu came from Jeff O. it should have a sticker on it telling you what it's got done to it.

 

[94TSiBeast]

ok i'll try and take a look at the chip/ecu. But I'm thinking about getting DSMLink and have it dyno tuned here before to long.

 

[4G63_fiend]

I would definately start by taking a look at the sensor and see how tight/loose it is. No sense in replacing a part that is not faulty, so I personally would start there. Vibration can also cause these things reading irregularly. Are your balance shafts still in? Do you have Poly motor mounts? Are your mounts in good shape? I know you said it happens some days and some days it doesn't, but like sordid said, have you noticed if it happens right after you take a turn or shift? Anything in particular that you may notice causing it could be a hint that it is not properly installed or it went bad. Do you have a way to test the sensor with an Ohm reader? Not sure what the spec is, but I am sure it is out there. Any input on that guys? I have never had a problem (knock on wood) , so I would not know first hand.

 

[amirmetal999]

whats your target afr ? whats your fuel type ?

 

[hotrodssnova]

The knock "sensor" is an electronic microphone. You can't ohm it. Phantom knock will definitely take the wind out of your sails.

Try what bastard suggested and unplug it, go for a short drive, and see if it happens. That's a FREE test, and you can look at the sensor while you're down there.

 

[4G63_fiend]

So is there any other way to test it other that to unplug and go for a drive?

 

[CrackedDSM]

So is there any other way to test it other that to unplug and go for a drive?

Test it the same way you would a microphone. Tap it. Watch your logger obviously while you're doing it.

 

[4G63_fiend]

Haha makes sense. Now that I think about it, don't they use some kind of stone that picks up the vibration?

 

[bastarddsm]

Test it the same way you would a microphone. Tap it. Watch your logger obviously while you're doing it.

Lol, no it doesn't work like that. The ecu has a high order bandpass filter that keeps everything outside of the cylinders fundamental frequency out. I can't remember 100% but I believe it looks for the 2nd harmonic, somewhere around 12khz. Not only that the ecu only listens to it for a very short period. IIRC, its about 10*btdc, to just a little after TDC. So the chances of "tapping on it" and getting the right frequency at the right time is very small. I would say if you tap on it, and it registers knock, it's junk. I do know people have connected them to a recording device and actually listen for knock through headphones.

In all honestly, a new one from oreillys is cheap, and new. The old ones are 20yrs old, there is some tar like substance in there that helps dampen out some frequencies.

I also know it doesn't take much to have phantom knock blow up though. Exhaust rubbing, bad motor-mounts, ect.

 

[Hitman9390]

Hey guys, First off im sorry to but in on this thread to ask this but how to you start a thread? Just started on this website and could really use the help,

 

[bastarddsm]

Lol, no it doesn't work like that. The ecu has a high order bandpass filter that keeps everything outside of the cylinders fundamental frequency out. I can't remember 100% but I believe it looks for the 2nd harmonic, somewhere around 12khz. Not only that the ecu only listens to it for a very short period. IIRC, its about 10*btdc, to just a little after TDC. So the chances of "tapping on it" and getting the right frequency at the right time is very small. I would say if you tap on it, and it registers knock, it's junk. I do know people have connected them to a recording device and actually listen for knock through headphones.

In all honestly, a new one from oreillys is cheap, and new. The old ones are 20yrs old, there is some tar like substance in there that helps dampen out some frequencies.

I also know it doesn't take much to have phantom knock blow up though. Exhaust rubbing, bad motor-mounts, ect.

FWIW, on my car I 99% of the time roll with the KS disabled. Normal combustion sounds very similar to slight detonation, and they sound even close the more you turn it up. The other part of this, is that my car defiantly traps higher showing a few counts of knock and a little bit of pepper on the plugs, and that's no suprise, the faster the combustion is, the higher the efficiency, to a point. I'm not recommending that you do that, I'm just illustrating, that a little knock here and there, probably isn't gonna blow it up.

 

[CrackedDSM]

I would say if you tap on it, and it registers knock, it's junk.

I should've been more specific, that's what I was referring to. Good catch.

 

[bastarddsm]

For any of you guys looking for some late night reading https://groups.yahoo.com/neo/groups/dsm-ecu/files/1g/Hardware/

This is a good description of how the knock sensor works.