help.... again..... so close to scrapping my car.

[jib136]

yet again i have another problem!

i am know getting a stupid high knock reading at full throttle aroudn 4,700rpm. it hits between 75-80knock.

what actually causes knock? like what effects it. spark? air? fuel? im running out of stuff to change/check.

any ideas will be helpful.

personally i think the only way to sort this problem is out the scrap the car...

 

[Jordan]

Pretty sure it's air fuel related dude. Knock is where air/ fuel pockets ignite before the spark from the spark plug, could be temperature related also.

im no mechanic however so can't really advise any more than that

 

[Jordan]

Just a thought, have any settings been changed on the hand controller?

 

[spoonman]

what fuel are you running, what spark plugs, what boost/ turbo / injectors / fuel pump, what computer, has the car been tuned, and if so what fuel was it tuned on and what was the air temp? have you changed anything on the car that changes O2 density since the tune?

Do you feel the cars ecu retarding the engine at all when this happens, aka cutting heaps of power of to prevent damage

Also look in your engine bay around the knock sensor for anything that might be causing a vibration or noise that its confusing with knock, something loose, something not fitted right.... general muppetisem modification

Knock is pre ignition detonation, or the air and fuel in your cylinders igniting before the spark plug ignites it, causing the piston to take a impact before its designated ignition down stroke, and basically if you were the piston its like getting punched in the face instead of getting pushed in the direction you are trying to go in.

It can happen due to too much heat building up on some part of the cylinder chamber, piston etc from not having the right amount of fuel to air.

 

[Auss15]

As spoonman said, it can be related to timing, AFR's, plugs, injectors maxing out, tunning isues and it can also be related to drive train noise. Personally I would be starting with the tune first...

 

[jib136]

Im running vpower fuel. Doesn't matter what boost setting its on. Does it every time at 4,700rpm at full throttle.

Im running nismo 550's, z32 afm, td05-18g turbo and ecu is power fc with a walbro pump.

Where abouts is the knock sensor on the 15?

 

[S15AK]

have you let a mapper take a look at it? sounds like it could need a map looking at..

 

[JDM_virgin]

i would just like to point out that pre ignition and detonation are two entirely different things.

detonation is what causes the knock and this happends AFTER the ignition spark. it, as jordan said is caused by excessive heat build up or by unburned fuel in the ignition phase. the knocking occurs at 6400Hz but varies between iron and aluminium. the knocking is not caused by two flame fronts colliding but by the sudden sharp spike of the second ignition and sound slike the engine has been hit with a hammer. its not necessarily destructive but means the engine is not running at optimum and can cause problems later on. these include: broken ring lands, pitting to crown of the piston, overheatinga nd therefore scuffed pistons and bores and broken spark plug ceramics.

pre ignition occurs BEFORE the ignition phase and occurs when pressure in the cylinder is at its lowest (BDC) and is caused be tiny carbon deposits that are still red hot in the cylinder or and overheated spark plug tip. as the piston rises from BDC the fuel air mixture is injected and its at this point the whole lot will ignite as the pressure is low so anything will ignite it. the result is a rapid burning of fuel that is being compressed by the piston as it rises on the compression stroke. net result- huge temperatures in the chamber 1800+ deg C and you end up witha huge hole in your piston. if pre ignition occurs the piston may only last 1 maybe 2 cycles before melt down.

i would say that your timing chain has jumped and that the spark is now too advanced therefore causing an increase in temperature and therefore detonation. i dont think its fuel unless yoyuve imported it from somalia and its like 90 octane or something. so id be checking how slack your chain is. also you will need to look at the pistons once solved as broken rings and crowns usually go undetected

 

[spoonman]

your knock sensor is under your intake manifold, little sensor screwed into the side of the block, its listening for noises that it detects as being dangerous for your engine, as in a ignition before or after as the text book (JDM_virgin) has stated.

Can you hear a noise sort of like ball bearings being thrown and a tin surface when at that rev, if that makes sense.

keep in mind that a knock sensor is not going to decipher the difference between a noise inside your engine and a noise near your engine if it is emitting a very similar sound, people have found that there engine is being retarded and the knock sensor is screaming blue murder only find that something has come loose and is being bashed around inside the engine bay and is making a noise that's being picked up as knock, not very common but does happen.
This is why your tuner would of had a set of headphones on when tuning to listen for any noises related to a unhealthy engine

 

[JDM_virgin]

text book. i like that one, its only because im doing a degree in mechanical engineering and this is probably the first thread ive read that i think i can actually be some help on haha

get it checked to see if its running lean or rich as that will narrow it down a lot. also as spoonman said, check for anything loose too

 

[spoonman]

all good dude, if the text book says that then its better then the opinions of the majority

 

[Auss15]

Seriously,get a tuner to look at the map, takes the guess work out and saves further damage. End Thread