I have heard that the spark table is chosen from the history of knock events, when the threshold is met the low octane table is used until the fuel system determines that there has been a refill and then reverts to the high octane table. If you disrupt power from the battery it will resets the PCM to a default engine condition using the high octane table.

If you log the engine timing you should see which table the PCM is using. For tuning purposes the tables are mirrored and then reset afterwards.

If someone knows different please chime in.

 

I don't know if the PCM would detect a refill or just use a certain time delay for going back to high octane table.

 

Bill,

I had heard something similar, but then heard that it was not true. I have seen for myself, though, that on key-on there is a J2178 message transmitted on the data bus (don't remember the source address) which indicates how much fuel (in liters) is in the tank. So it is possible that if the ECU sees this number increase from the last key-on, it resets the knock learn factor.

Then again I have noticed that in ordinary driving there is occasionally a small amount of KR (generally less than 1°). Others have observed the same behavior on their vehicles, so it is also possible that the ECU is "probing the upper limits" occasionally during the driving cycle.

So the question is: Which method is used? Tank fill reset? Contiuous probing? Both? Or neither?

Inquiring minds want to know.

 

 

or just use a certain time delay for going back to high octane table.
>>
+1

Maybe after the octane level is increased and keeps knock in check for a while then the pcm will try a higher timing table?

 

Sorry for the late response.. if you calculate the speed of sound (c=sqrt(krt)) you can determine how many times per second the noise will bounce off the cylinder walls after knock has occured. The period is determined mostly by bore size. Larger the bore size the longer it takes for one period to occur and therfore you'll listen for a numerically lower frequency.

K for a air fuel mix is generally accepted as a 1.35

 

translation of the bible from original hebrew text.

3rd century b.c -greek
1st century a.d-latin
2nd century -syriac
3rd century-coptic
4th century-ethiopic/gothic
7th century-arabic
8th century-anglo-saxon,slavonic
9th century-norman,french
12th century-italian,spanish
13th century-german,dutch,polish
14thcentury-persian,norwegian,czech + english.

now in regards to the ???,I'll reiterate in another way,

stop the nitipicky crap,I am what I am, it is your problem,not my problem.

 

I have fitted the aircond belt to a slightly binding compressor clutch
which just brisked when i free spun the pulley around,it made a very slight tinny noise,not enough to warrant changing a pre gassed unit.After hooking up the aircond belt,the car seemed to run very sluggy indeed (too much to warrant just one pulley anyway)however,did so for a fair few days before finally it somehow seemed to revert back to its normal itself for the better.

what very well may have happened is the knock sensors somehow picked up that slight tinny noise and defaulted the map to safe slug mode.

somehow the compressor binded less over time,then the less evident tinny sound promoted less of a signal to the knock sensors,which interm must have told the ecu like hey its not that bad now,so lets give it more advance.

I never liked knock sensors,i knew one bloke who did over 200,000 miles
driving flat stick at will,with slight pingining at lower rpms,(to his preferred tuned state with the electronic dizzy) past 6,200rpm on the ol hway patrol 351v8,with never an issue! He was experienced and knew that on them cooler days and evenings the gains were more than worth it+ the car performed consistent night or day except little rattle here or there on them hotter days+certainly more consistent than any factory stock programed ecu with its knock sensor partners that I've driven anyway!that was way back in ol school days without them knock sensors.

Fortunately nowadays, we can cater for different ambient temperatures via software tuning,however when a knock sensor does not account for other variables like aircond pulleys or noisier than new pulley bearings,id rather a/bypass the knock sensors completely,provided there was not noteable pinging afterwards towards the top rpms ranges, or b/with them beaut tuning tools,re adjust the factorys lame settings and limit the amount of knock retard to reasonable standards,just like gregory mentioned,has on both his maps.

 

did you just say knock sensors are bad?

 

Thank you! Keep posting up good info!
My engine has a diff bore size and I have always thought I hear it knocking sometime but the PCM never picks it up.

This could be something for me to investigate in.

 

there is a ramp rate where it will increase timing at a certain interval as long as it doesn't see knock again....i believe factory is like 15sec after it has retarded it will start increase if no further knock has been seen(that is a iirc from when i was programming in hptuners)...it will also automatically reset to the high octane if the fuel level is increased thinking you added higher octane fuel...if it sees knock it will again retard as needed

edit:you can change the interval to start adding timing and rate of speed it ramps the timing back in as well

 

Good info, I have always wondered how the PCM decides when to try more timing again after knock retard. Once in a while I hear a little knock from my engine, I hate hearing that and wondering if I'm now in the low octane tables for a week or two.

As far as high/low octane tables, it sounds like there is a range of values the PCM can use depending on how much knock it senses, as opposed to simply high or low. What exactly is a table?

Does anyone know where I could find some sort of charts that would show actual timing values relative to engine load or which ever factors the PCM uses to adjust timing for specific engines? It would be intersting to see one for my car.