DFCO timer / delay constant?

[mourat]

I just got around to playing around with the tune on my own car, and noticed that I dont have the option to alter the timer for DFCO, it seems like when i let off the gas, it takes a good 2-3 seconds for DFCO to come on.

I disabled CFCO because I like a clean decel, I know lots of people like the popping, me not so much.

However I still have some popping before DFCO comes on full, anyone know where in the E38 pcm the DFCO timer is?

Mine is a 2007 C6 corvette, ls2.

Thanks.

[07MontRedcp]

Take a look at Engine > Fuel > CutOff , DFCO > Switchover Delay. Maybe that is what you are looking for.

BJK

[mourat]

Hmm... I thought that was something different, switch over delay as it states there is when fuel cut off ie. REV limiter is active, if its active more than 5 seconds it uses throttle to control rpm instead of fuel/spark.

Ie. nothing to do with DFCO?

[07MontRedcp]

Hmm... I thought that was something different, switch over delay as it states there is when fuel cut off ie. REV limiter is active, if its active more than 5 seconds it uses throttle to control rpm instead of fuel/spark.

Ie. nothing to do with DFCO?

Looks like I was in to big of a hurry and thought I read Spark to Fuel rather than Spark/Fuel.

BJK

[mourat]

no worries, hopefully someone knows the answer, seems like E40 and older 411 pcms have it but not e38, I emailed a few places to see if its just hidden.

[MikeOD]

mourat, did you ever find anything? I'm playing with DFCO entry/exit spark in my car to try to control the popping some more, but I also think there's a delay timer that we might not have access to in the E38.

[bluetorp]

Watching my wideband on decel, there's definitely a second or two of delay before it starts going lean. Can't comment on the existence of a delay parameter that isn't in HPT yet.

My Camaro likes the stock ZR1 DFCO Entry/Exit spark values. No popping anywhere during DFCO. Don't recall noticing any difference in engine braking, either.

[MikeOD]

Mine also likes the ZR1 Entry/Exit spark...I flashed it in yesterday morning and noticed that DFCO is now no longer accompanied by any popping when it starts, the ridiculous occasional backfire I used to get when tipping back into the throttle quick during DFCO are also completely gone, and the car seems to hold speed coming down hill in gear, and slow down in gear when I downshift the same as it used to...so I'm happy about that.

On the LT1 PCM...way back in the day (the 8051...OBD1 and I believe the first flash based GM PCM) there is a delay timer constant, which if I remember right was set to 2.5 seconds on every cal I ever saw...I used to always change it to something more like 0.2 if not 0, and I always liked how that performed.

I asked HPTuners support about this with the gen 3 PCM's when I had my LS1 car and they said it wasn't there or couldn't be changed, but I don't know about the Gen 4 PCM.

[mourat]

Yup, basically I found my fix by changing the DFCO & CFCO entry/exit spark to 20* and that gave me a clean decel

Also, changed the delay to 1 low res pulse instead of 0 and comes on sooner, almost like 0 made it default to 2-3 seconds. I changed it using another program, dont know if I can mention the name here, and in pic I left name out since HP tuners doesn't have that table.

Now here is something to keep in mind, I haven't tested it but I think the delay also comes from entry/exit spark, the PCM waits until it gradually brings the timing down to whatever you put in that table from what you are at now. So say you are crusing at 30* timing, and you have entry set to 10*, it would have to wait until it gradually brings timing down to 10* before decel, this adds time, so the closer the entry and exit is to actual timing at those crusing speeds the faster it will cut fuel after entering DFCO, cuz I logged it, stock it enters DFCO fairly quick but then waits another 2-3 seconds before cutting fuel, if you watch the timing, if I recall it waited until it brought timing down to "entry" I would have to recheck later, hope this helps.

Also I changed the throttle park position at certain speeds, my decel is spotless clean now zero pop.

Also by setting the timing up to 20* I believe it makes it a bit quiter when you let off before it cuts, since 10* causes some of that unburnt fuel before it clears up to be louder since it fires it closer to the exhaust stroke, just like a car running 10* timing is typically a bit louder than 40* since less of the exhaust stroke is introduced directly into the exhaust when the valve opens there is less "fire", ie. 0* a lot of your combustion is still happening in your exhaust and thus why exhaust glows and thus also why its louder. Figure I add that little bit

Ohh another thing I noticed helped is delaying the integrator learn so you dont get that huge rich/lean spike we sometimes get with headers for no reason, and I think when that happens if you are about to go into DFCO it would cause a pop as well, delaying itegrator learn got rid of most of those "spikes"

But basically if you change the timing entry/exit to 20* that makes a huge difference, sorry haven't been on here busy doing things around the house.

[wyochimneysweep]

Yep the enter and exit controls speed of dfco and also theres a table for how much spark times sec is removed on decel to get to your dfco enter spark

[MikeOD]

HPTuners...PLEASE add the stuff Mourat is showing in his screen shot from TC. I don't think it's wrong to mention other software.

[wyochimneysweep]

U don't need that stuff. Got my dfco coming in about a sec after I start decel

[MikeOD]

U don't need that stuff. Got my dfco coming in about a sec after I start decel

I'm not satisfied with mine, and the delay is what will allow me to put it where I want it.

[wyochimneysweep]

Post your tune I want to look at it if u don't mind and how fast do u want it to come on? I got mine so at the 2 second rule behind someone if they hit the brakes and I let off the gas it goes into dfco before I got to hit the brakes

[LEDbetter]

I was looking at some stock tunes for efi live (06 CTS-V and 07 Silverado) and there is a whole second of difference for DFCO to start.