Quote:
Originally Posted by solidONE
I think there is are tables in the rom where you can program in the "tip in" ignition retard according to the amount of change in throttle position and another table that control the amount of additional fuel is added at tip in according to the percentage change in throttle.
I'm also curious about this tip in knock that the ECU is detecting particularly at higher temp operation. It seem like it's impossible to totally eliminate nomatter what you do with the tip in enrichment or ignition retard. Yet, it seems to disappear when temperatures cool.
|
First of all big thanks to @
arghx7 for the write up. Take a lot of patience to do this.
So most tip in knock is due to two main reasons:
1. The actual engine load is not always determined precisely because most Volumetric Efficiency maps & MAF sensor based load determination is calibrated at steady state operation. What happends during Tip IN and also Tip Out for that matter is a transient air flow problem that most OEMs still try to model using manifold filling models but still fall short in properly estimating load. So when the engine load/airflow is higher than what the ECU estimated the spark timing would be over advanced for the load and the fueling could go
slightly on the leaner side until the O2 sensors correct using feedback.
2. As the load changes the cams have to move to a different position based on their lookup table. Most times these days they actually have to move a lot because OEMs try to use cams a lot for fuel economy (Lowest VE cam timing) and they have to travel a lot to go to their peak power positions (Best VE cams). Now this takes a few tenths of a second to happen so it is pretty fast but still slow enough for a cylinder to knock because the spark was calibrated in steady state for a different set of cam positions but the cams are not there yet meaning the spark and cam positions are not exactly where things were calibrated in steady state.
Some OEMs have calibrations to add and subtract spark based on how far the cams are away from their calibrations. Trust me it is better not to try and calibrate that on the street or on the dyno because it is not worth the effort and better to leave those cals as they are. If done wrong the engine can bog down during transients.
One thing I would encourage everyone to do soon after flashing in a cal is to let the engine learn the background noise. This is usually learnt at low loads and across the engine speeds. So basically 1st gear slow pull to redline a few times. Not WOT
once the ECU knows the background noise it will be able to determine knock more effectively instead of thinking the valvetrain noise to be knock.
The amount of spark pull out is usually based on the freqency and severity of the knock signal so learning the background noise level will make the knock sensor detect the right severity.