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Discussion Starter #1
When I'm cruising around and accelerate to 3500 rpm my car feels like its choking and I get a whole lot of black smoke. It goes away as soon as I apply more gas and pick up some boost... At first I thought it might have been the tvis opening late or something... but i was told it opened up at 4200? Any ideas? new cap, rotor, wires, plugs, not sure about the coil. Timing is dead on, I boost fine in every gear. Just wondering what is causing this.
 

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"... accelerate to 3500 rpm my car feels like its choking ... goes away as soon as I apply more gas and pick up some boost..."

Classic description of knock response.


bill

bill
 

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Discussion Starter #3
Wouldn't I get some type of CEL if it were knock sensor? I just tried again and i experienced the same thing at around 3k rpm flat... Why would I be knocking though? I'm 100% stock with the exception of an intake and gutted cats. All parts are OEM, how can I check if its knock for sure? and how come I only knock off boost? I was getting ready to point my finger at the ignition coil but now you just got me worried ;\
 

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Discussion Starter #4 (Edited)
O.k I pulled codes and nothing related to knock sensor came up (34 + 35 since I was messing with pressure sensor)

could a bad coil give me same results? because even when I'm at WOT at higher rpm and not hesitating i still get lots of smoke... and i still rev pretty slow to redline...
 

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There is no CEL associated with a knock input. The knock sensor/knock response loop is just another component in the ECU's engine management program. The 3sgte runs a very agressive timing program, and relies on the knock sensor to keep things under control.

Knock occurs under certain conditions in virtually all gasoline engines, and is more common (and somehwat more dangerous) in forced induction engines. That's why it is eq3uipped with a knock sensor and programmed resonse.

It hears the beginnings of knock long before it is either audible or dangerous, and retard the timing to correct it.

Its just doing what its supposed to do.
 

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rony said:
When I'm cruising around and accelerate to 3500 rpm my car feels like its choking and I get a whole lot of black smoke. It goes away as soon as I apply more gas and pick up some boost... At first I thought it might have been the tvis opening late or something... but i was told it opened up at 4200? Any ideas? new cap, rotor, wires, plugs, not sure about the coil. Timing is dead on, I boost fine in every gear. Just wondering what is causing this.
Same symptoms I had except for the black smoke.. I also had no cell. Put in a new knock sensor, problem solved.
 

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Like Bill said, it's a bad knock sensor. It's retarding the timing, causing the delayed response. The sensor has gone bad and is retarding timing even though there's no problem. Typically it retards the timing at very small incrimients, to where you don't even notice it. Read THIS and understand it, it'll explain exactly what's going on.
 

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No, bill did NOT say that.

If your getting knock response, your knock sensor is working just fine. Its doing exactly what its supposed to do.

If your knock sensor is defective, you will get a CEL, and a code #52.


bill
 

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Discussion Starter #9 (Edited)
So it could in fact NOT be knock? Just that the sensor is bad? Also... where is the knock sensor located? :smile:

edit:

So if the sensor is NOT bad, then what should I do to fix it? I mean... what could cause a completely stock car to knock? No matter what the temperature is outside... I'm not boosting more then 11psi... I'm not sure what could be causing this.
 

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Here is a key portion from the link paul posted (which I wrote):

"Knock is most likely to occur at low to mid RPM, (3000-5000) in upper gears, at WOT, under boost and under increased load. It is most common in cool weather ( mid-30s and below) or in hot weather (90s and above, but can sometimes occur at moderate temps as well. The response cycle will typically be felt for only a few seconds, and the engine will again feel ?normal? after the correction has been completed.

This ?self-correcting? characteristic is the most distinctive symptom of the knock response. The other common causes of a rough engine, limited fuel delivery or weak ignition, are not likely to improve at increasing RPM and/or increasing boost.

And a knock input/knock response DOES NOT mean something is ?wrong?.; it simply means that the ECU is adjusting the engines operating parameters in response to the environmental conditions that it sees."
 

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Sorry bill, i meant to say. "Like convict said" but your reply was the one that showed last so i typed you by mistake. If it's not the knock sensor gone bad what else could it be? I assumed it to be the knock sensor because i could have sworn i read a post a long time ago where someone was having the same problem and replacing the knock sensor fixed it.
 

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Discussion Starter #13
ramicio said:
you could also have a boost leak. richness can cause knock too. it's not always from going lean.
My gauge reads perfect and I seem to hold boost fine (omori 46mm gauge) I've inspected all hoses thinking this was the case as well.
 

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how closely did you inspect the hoses? i refused to think i had a boost leak, and inspected everything, but not carefully enough. a tiny hole that can barely appear can open up a lot under boost. also, your gauge will still read the same. the turbo will just crank out more air to reach that desired boost level.
 

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Again, knock input/knock response doesen't necessarily indicate that anything is wrong. Uncer certain conditions ALL engines are prone to knock, and forced inductin engines are more prone.

If it happens occasinally, there is probably nothing at all wrong. If it happens all the time, then there are some basic things to check. First is timing, then compression. as engines get older, carbon deposits raise compression, which is one of the things tha tcontrubutes to knock.

If you had read the material at the link, you would have found these additional links that give you more info on what causes knock, and what actions to take.



http://www.misterfixit.com/deton.htm

http://www.hastingsinc.com/Service Tips/detonation_and_preignition.htm

bill
 

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Discussion Starter #17
93 Octane, strange thing happened on the way home. It was much colder then this afternoon... and it only happened twice, both times were intentional. The magic gear seems to be 3rd at around 3k+ but less then 4k... It does not happen in 4th or 5th. Question: Can bad ignition components cause a bad setting to be set when adjusting timing?
 

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"It was much colder then this afternoon..."

Then that's the reason. My flawless '91T would do the knock repsonse routine (in 3rd gear, at ~ 8-9 psi)) anytime the temps fell into the 30s. And I always ran 93 octane.

As i posted above: "It is most common in cool weather ( mid-30s and below)".

Quit worrying. Everthing is normal and nothing needs to be "fixed". Your engine management system is working perfectly.

bill
 

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Discussion Starter #19
^ but it wasn't in the 30's today ;( I'm from miami, lol much colder for us is like 60's lol.
 

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that sounds like a boost leak to me. The black smoke kinda drew me away from thinking its knock response. Your getting air metered in and its not getting into ur motor, but ur still getting the fuel for that amount of air. Id say its a boost leak. If its that big then u will 'hear' it. Sounds like a jet plane...sorta.

mark
 
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