trex92

Hmmm... i wonder if any other users of SAFC2 users out there are experiencing the same thing as me. I noticed that when the weather is hot like in the afternoon, the knock sensor reading for my SAFC2 goes haywire and very erratic even when I am driving on the highway. The reading jumps up and down and sometimes goes very high like 80. This happens only when it in the afternoon when it is hot. In the mornings and late evenings, the reading is stable with no problems.

I'm driving a Putra with SAFC2 installed. I have tuned the SAFC knock sensor setting at 1500rpm and 4000rpm already and I did it a few times but problem still there.

     

endless551

did u mean the O2 sensor signal?

     

trex92

Nope, not the O2 sensor signal. My Putra is a 1997 model, its without O2 sensor. I mean the engine knocking sensor. I was told that the sensor is something like a microphone and it detects engine noise in order to gauge the engine knocking level.

     

endless551

It is actually a piezoelectric element not a microphone. Microphone is used by tuners for audible signal.. anyway.. that sounds weird to me.. Does ur engine timing retard or so when the signal flactuates?

     

trex92

does the piezoelectric element works on sound? Coz my bro told me if use a hammer to knock on the engine, the sensor would pick up the sound as engine knocking too wan.

Nope, my engine running smooth when the signal fluctuates. No backfiring or jerks...

     

endless551

When the hammer knocks on ur engine it generates vibration which in turns generate sound. ENgine knock occurs in some specific frequency range, the voltage range of the sensor is adjusted to detect such frequency. Piezoelectric/ accelerometer actually generates a voltage when vibration/pressure is sensed. I'm not aware of other type of knock sensor in the market.

Get ur car dynoed to obtain ur AF ratio curve. Would give the tuner a much better indication of wats going on. Let the person know when u get such signal, on WOT (wide open throttle) or just cruising.. THere could be mild knock detected but not enough for the ecu to retard the timing, I would say its a badly tuned afc. As on hot day high engine temp can cause pre-combustions which in turns causes knock. Go speak to some1 that knows how to tune it instead.

     

trex92

okie, thanks for ur advice... it could be a badly tuned AFC coz i played around with the settings myself. :)

     

MaNofWaR

fm my experience it does fluctuates a lil...but not very high value... about 60 or so.... anyway there is also a note in the manual saying that sometime the value indicated is just a rough guide.... happens to me too....

     

endless551

don't ever fiddle around with ur AF ratio by guesstimation.. Its the most common culprit for blown engines.

     

trex92

Hmmm... no worries, my settings so far has been conservative. never above +10% and never below -3%...

     

trex92

manofwar, mine fluctuates like 0 ->70 -> 0 -> 30 -> 0 -> 80 etc and it happens only in the hot afternoon... is urs like this too?

     

MaNofWaR

not really...mine only goes to abt 30+

     

mengz

the highest i ever got was 30+ on hot sunny afternoon after i rev the car like crazy. other than tat. usually afternoon around 10-11. morning at night around 5-6.

anyways during day/night u set ur knock sensor? coz lets say if u set it at night ah, then during hot afternoon ur knock will show very high. so the best is hot afternoon, u let ur car idle for like 10-15mins, then u set the knock at 1500rpm and 3500rpm. off engine on engine again and see how it goes ler. anyways this is just a suggestion la. but bcoz if u say can knock like 80 plus, thats quite high. like some forumers said, maybe wrong a/f ratio setting qua. best go to a reputable tuner and tune ler. but if after tuning, still knoch very high, maybe could be ur sensor rosak, or ur engine got prob ler :P

     

Kenboy

you may need to reduce your ignition timing if extra fueling doesnt work to reduce ur knocking.