knock sensor tip in

[tabbruzz]

Guys,

Need some help here with my 99 vette. My tuner changed the values below and I wanted to know how they work. I know it was an attempt to desensitize the knock sensors, but why change these when the other tables could be changed?? And those other tables were updated to desensitize a bit......What I don't want is my knock sensors shut off and that TPS delta setting is scaring me........please school me here as I did read the HP tuners def of these, but it's still not clear to me.

Knock Sensor Tip In
Min TPS- 1.99% (not changed)
Max TPS- 60% (changed from 50%)
TPS Delta 3.008 % (changed from 99%)

[tabbruzz]

anybody???

[murfie]

So there are a few situations that the engine becomes more prone to detonation. The calibration allows different knock sensor levels of sensitivity for these situations. One of these is tip in, or a sudden increase in throttle. The airflow through a throttle body has the most increase in airflow into the cylinder in the lower angles. So 5* to 40* will be a larger gain in airflow than 40* to 90*. You can think of how the throttle effects manifold pressure/vacuum to easier understand this. Octane is the main determining factor of knock, but I also find the error in OL fueling is what largely causes the tip in detonation. OL fueling is purely a guess and by the time you get feed back from O2 sensors it's too late, so even calibrated to an OEM level, error can be large enough to cause detonation. Most tuners don't even try to tune fuel in these areas and just desensitize the sensor, during this brief window. The OEM's do a very good job, so their tip in knock is well controlled and sensitivity is left relatively high.

The min and max TPS define this lower throttle angle range. Basically if the throttle is increasing while between these TPS values, the KS level defined in the tip in TPS table is used. Its higher values define a higher threshold to trigger spark retard.
The TPS delta defines what changes in TPS classifies as a TPS tip in. 99% is the OEM leaving sensitivity relatively high, basically the tps needs a fairly large change to use the less sensitive knock sensor levels.
What your tuner has done, is basically make it so nearly all throttle increases below 60% the knock sensors sensitivity level is the TPS tip in values table. Its probably not that bad if that's all they did, and what ever knock issue you were having lessened. Depending on where the MAP is allowed to get to at these low TPS, and the sensitivity level calibrated in that table, this could allow some short, but strong detonation, I've seen cars build boost at 50% throttle. It would probably just be a brief occurrence, but if you do any canyon driving, road course, scca type racing, you know you can have many tip ins in a short period of time. Knock usually doesn't hurt an engine instantly or the first time it happens, but over time it wears on the components.

The table you want to make sure they didn't get too aggressive with, is the "vs MAP vs Cyl" ECM 12956. This table multiplies the sensor level, increasing the value making the sensitivity less. High vacuum areas have a stock value of 4, basically making the knock sensors highly desensitized at low MAP values. This is fine as the energy in the amount of cylinder air mass in high vacuum is so low, risk of damage is not likely.

[tabbruzz]

murfie,

I really appreciate the information you provided....Great stuff. Very helpful.....My tuner did not touch the Map vs Cyl table, only Tip in TPS and vs RPM vs Cyl where he increased values a bit in some cells. The largest changes seen was in Tip in TPS where we changed 0-3200rpm from 11 to 15 and 3600 -8000 from 11 to 13.......Now the reason I had a dyno tune to begin with was I added a SC to my 99 c5. Now it always had knock for some reason at lower rpms say 2400 or 2800 to the tune of 1 to 3 degress retard. This did not always happen but did pretty often......The only other knock was seen at 5200 to 5600 rpm when WOT. To stop this we did two things, put timing to 12 degrees in these cells at higher kpa and the knock retard settings I already discussed.......With this new info, would you be concerned with the knock settings? My fear is that knock would not be detected when it really needed to be......Thoughts....I can send you the file need be as well.....Again.....thank you very much

[murfie]

For me personally, I wouldn't want to desensitized the knock sensors running pump 91/93. E85 or dedicated to race fuel I would be ok with it.

If your tuner has done a combination like yours many times, and has never had to do it, then I would find what's different and fix it. If your tuner has many combos like yours where he has done it in nearly all of them, and there isn't a history of customers with hurt motors, I would say you are fine.

[tabbruzz]

Ok, sounds good.....Thanks