Hey guys, ever since i installed my SAFC this winter i have been able to monitre my engine for knocks. Since this summer has started, my engine has been shoiwng some knock (7-18) even today, at idle, after 5 mins of running on a cold start, its been showing knock. No audible knock. 54K on origional motor. Ive been running 93. On cold nights it doenst knock AT ALL but any time its a warm day it knocks. DOes anyone know the cause or cure for this? Even while i water-treated my motor today it STILL knocked during treatment. I dont understand. I thought knocks was caused by pre-ignition, which i thought was caused by the rotor surface or housing surface getting too hot, high enough to support pre-ignition. Sucking cold water directly into the upper intake manifold shouldve cured this. Any suggestions is appreciated.

87TII

 

some knock is ok as much as i understand. when it gets very high i think triple digits is when it gets bad.

i dont know. this was on my bros wrx. i know a rotary might be a bit more sensetive. but in any case, it would still show knock on that car. around 1 to 10 sometimes. just interpherence i think.

i would worry about it unless it gets higher than normal.

 

What you are possibly seeing is just electrical interfierence or noise, which ever is the correct term. Its says it right in the manual. I have the same on mine and every SAFC I see.

 

im having doubts that its electrical interference...Even with a 1% correction increase in fuel, the knock goes away. I thought our motors already ran rich as hell lol. Replacing my o2 sensor might help i guess. But yeah, it couldve been doing this it's whole life, just now i can monitor it. hmmmmmmmm

 

the knock sensor is a microphone, it picks up noise. it is tuned to pick up knock, but it will also pick up other drivetrain noises as well.

but if you richen it up and the knock goes away, you have your answer. "rich as hell" is relative.

 

So far, what I have seen is that the knocking is DIRECTLY related to ambient air temperature. Cold start or hot, coolant at ANY temp, at idle or in vacuum or in boost (when not correcting), it knocks. Today its 82F and i started it cold and it was already knocking at 7. Im wondering if my IAT sensor is bad. Or, it could just be bad OEM fuel maps for high intake air temps... But it is true knock, adding fuel completely eliminates it...This takes some more thinking. Any ideas guys?

 

through deductive reasoning i have concluded that....


your car is broken.

 

well the S-AFC not known to be an accurate knock sensor, its just a damn piggy back

 

cptpain - My SAFCII is not a knock sensor at all, all its doing is showing what my OEM sensor is reading, which i believe is accurate. And i realize all it is is a "damn piggy back", but that still doesnt explain why my motor is knocking. I see alot of threads on here with people having this same condition, yet noone seems to have an answer.

Haha, and yes, my car could be broken. I'm just trying to play it safe.

Anyone have luck with alcohol injection?




P.S. Since our IAT is incorporated in our AFM's, im gonna recheck the AFM recall we have to make sure mine isnt one of the defective ones, i gotta wait till tomorrow to check the database again (ALLDATA)

 

Unless turbos are different, the IAT sensor is completely separate from the AFM.

Also, they generally only run super rich under WOT.

 

hmm, ill have to check my sources again. (I see what you mean Sideways7, the sensor below the throttle body i believe? More research i guess. If this proves true, ill test it at the shop probably next week or the week after) Either way, ill double check the serial # for the AFM recall.

The problem is, ive been tuning based on my car's twin's AFRs which I know is a bad idea. Ill have a wideband in a couple months, I just gotta get outa college first (End of June Thank GOD)

 

The reading you see will also be higher then what is actually happening because of electrical interfierence.

There is a IAT sensor in the AFM. Between that flap and the IAT in the AFM, thats how the ECU determins the amount of air flowing into the the engine.

Not to be confused with the IAT on the manifold.

 

This i do understand, but it would make way more sense if it showed knock ALL the time, as in, cold days (all through winter no knock at all, or any day lately where its colder than 65-ish) but it only shows it on warm days (i.e. today, 82F outside, knocked the entire time 8-14)), which is why I'm a little worried. It steadily climbs the warmer the engine gets (peaks around 17 sometimes). The only time it'll do it on a cold day is when i take her home (300 mile trip) after about an hour itll show slight knock (7-12).
I'd almost think I'd see LESS knock now, if this was caused by electrical interference (mainly because heat increases resistance, and on a warmer day, the wires between the sensor itself and the SAFCII would have increased resistance, therefor showing less voltage(BTW I know what the SAFC shows isnt voltage from the sensor, but thats how piezoelectric knock sensors work))

 

Well I havn't delt with knock before but could it also be caused by a little to much advanced timing?

 

i've been thinking about that. I'm going to unplug my FCD and get back to ya

 

i dont trust an safc. period. could be ANTYHING!!

try modifieing and redoing some grounds on the main harness and see if that helps. its probobly just noise.

 

the FCD doesn't advance timing right?

 

So, how much fuel (%) have you pulled out of the fuel maps? You know that as you fool the ecu, the timing is not retarded correctly, because the ecu 'thinks' the airflow and engine load is lower?

You may just be exposing and alalyzing the basic flaw in piggyback a/f controllers.

Can you reset your fuel adjustments to zero and still read the knock numbers? This might be with trying, just for a referrence.

Good luck

 

well, S4 ecu's use the boost sensor for two things only: Fuel Cut, and timing retard at certain boost pressures. The FCD is a resistor to fool the ECU into seeing less boost, therefore no fuel cut. This will leave timing advanced more than intended from the factory, which could be causing my issues. But that still doesnt explain why it ONLY knocks at higher ambient temperatures. As stated before, on S4 Turbo II's the IAT is infact part of the AFM, but my dumb self forgot to get the serial number for the recall again, so ill have to check it tommorow.

As far as pulling fuel, im not pulling any fuel at all, im adding fuel. When Zero'd out it knocks more, with added fuel the knock goes away completely(0). Today is 60F. I started it, let it warm up, boosted all the way to 14psi and back, took it home, let it cool, and shut it off. No knock at all. More and more it seems to be directly related to ambient air temperature and nothing else. Im testing my IAT asap. I'll post what the results are

 

Maybe I misunderstand the whole basis of tuning fuel, but what does your air/fuel ratio look like when you add enough fuel to get the knock to go away? Is it showing mega rich, or normal? Do you smell raw gas from behind the car?

 

Thanks for clearing that up. So without the FCD, as boost creeps up, the ECU will retard the timing more?

 

the knock sensors equipped on these cars are pure crap, disregard any info it may be feeding you.


the main reason you are seeing more knock in higher ambient temperatures is because the sensor is located in a gel like substance, as it warms the gel becomes more soft and pliable and also picks up more vibrations, mostly of which are normal vibrations from accessories and engine operation. over years the gel liquifies and melts out of the sensor and the readings become very high.

as i said though, disregard what the knock sensor is telling you because it likely is nothing to worry about. they may have worked "okay" about 20 years ago but not anymore..

 

that is something i completely over-looked. I guess replacement is the only fix for that?

 

Yes, without the FCD the ecu WILL retard timing more (to the best of my knowledge) even though I believe it is only a couple degrees.