Originally Posted by
LETZRIDE
Just a few questions on tuning DFCO for a 2002 LS1 Camaro. My car is bolt ons currently with a 3600 stall, it appears as if I just do not hit DFCO conditions at all as the car always wants to command 14.7 while coasting, foot off the gas on the highway.
so I am trying to get a more aggressive fuel efficient tune on here for the street.
Looking at the DFCO tables, I have some questions/clarification that I need.
Starting under the cutoff, DFCO tab
1) what does hysteresis mean? To prevent from oscillating in and out of a selected value (turn off at a value of 1.00) a window is setup for enable and disable control. Hysteresis is that window. In this example, when a value his 1.00 it would turn off something, without hysteresis, when the value went to .99 it would turn on again. This would cause the enable/disable to oscillate on and off under normal conditions. If you assigned a hysteresis value of say .1, the signal could vary between 1.0 and .9 after satisfying the turn-off criteria of 1.00 and stay off until the signal hit .9. Allowing normal signal variances from causing on/off oscillations.
2) Enable RPM vs Gear > Entry - is set at 1500 for all gears it says the engine RPM must exceed this value? meaning what- that in order for DFCO to occur, my rpm must be above 1500 rpm while below my throttle threshold? Yes
The exit table is set to 900 and also says it must exceed that value...am I understanding correctly in that the exit number is once that RPM is below that number, you drop out of DFCO? Yes, based on the hysteresis as explained above
So in other words, your entry and exit values are your range in which DFCO operates? Hp tuners words this weird in my opinion...
3) my entry Baro is 18 exit is 28 kpa...again is my operating range only in between those values? That seems like a very small window? DFCO says you have come off the throttle and your Throttle body blade is closed and there is actually negative torque being demanding so there is no load on the engine. This will result in very high vacuum (low Map) and that is what is used to in part to trigger DFCO. reapplying the pedal will disengage DFCO and your map will then increase and in a stock setup with stock cam those are reasonable values. If you have a cam or a vacum leak, you may not be able to hit the 18 kPa trigger. To that you either fix the leak or increase the value to match the cam influences.
4) Can someone better explain the DFCO entry spark threshold? This is the degree spark advance that must be reached to turn the fuel off...what does this mean? My understanding of this value is as the spark is reduced in DFCO, it must be reduced to this level to enable fuel cutoff. Just another of the many triggers that must be satisfied to enable fuel cut in decel.
5) we have two spark advance tables- A and B... one is set at 100% tps the other is at 99%...do we not use these tables then? I The spark values are the set poins per rpm when in decel. I have to say I don't know what the TPS at 100% and 99% distinguishes other than maybe WOT vs Non-WOT...Hopefully someone else can help. Looks like a description deficiency perhaps :-)
6) What is the "Stall" mine is set to 800 rpm... Again under my understanding, under no circumstance can the fuel remain shut off at an rpm lower than 800 rpm, again a stock value where idle is like 550 rpm....a fail safe.
sorry if some of these are dumb questions... my problem is if I don't understand the explanation of each function, I can't strategize or figure out how to best set the car up. I wish Hp tuners had a better glossary/explanation of terms