DFCO with 16197427 running $OD

**FSJ Guy** · 02-11-2012

I have been trying to get my DFCO to activate more frequently. I have lowered the timer down to 2 seconds (from 6.5 seconds OEM setting).

i am now playing with the setting labeled "Maximum MAP for DFCO" located at 0x4934. OEM setting is 31 Kpa in the BJYN bin.

What does it actually control? Rather than a maximum setting for enabling DFCO, it seems more like the MAP has to DROP by that many points when the throttle is closed (as compared to when the throttle was open) before DFCO is enabled.

Yes? No? Other ideas?

There are times when I an driving and I expect DFCO to be enabled, but it never happens. And this "difference" theory is the only one I can come up with.

**gregs78cam** · 02-11-2012

I think it means that the map has to see less than 31Kpa (more vacuum) before DFCO is active. What Kpa does the engine idle at? There is also a RPM threshold or two if I remember correctly, try adjusting them as well.

I believe there is a map difference that has to be seen, yes but I thought it was labeled as such.

**EagleMark** · 02-12-2012

All sorts of settings for DFCO like TPS% too... not sure exactly in $OD. One thing you need to remember is get MAP at idle and go lower MAP kpa reading or DFCO will effect idle!

**FSJ Guy** · 02-12-2012

MAP at idle is 41 Kpa. There's a TPS % difference setting, too. It's called TPS for Deceleration Enleanment. I'm not sure if that's referring to DFCO or not. <shrug> It's at location 0x492C and my original bin setting is 4.7%.

It looks like if I want it to activate MORE often, I need to raise the Maximum MAP for DFCO, but keep it below my idle MAP value of 41. Right now, I can't get DFCO to activate unless I let off the throttle when I'm going 50-55 mph or faster. I'm not sure if it's the speed that is the issue or if there is something else (like MAP difference) limiting things. JeepsnGuns said he could get DFCO to active at much lower speeds. I'm not running the same base bin as he is, but I do have all the transmission settings turned off so the PCM thinks it's not running an electronic transmission.

**JeepsAndGuns** · 02-12-2012

I think the biggest thing between mine and yours, is yours is a auto. Most all autos I have seen drop to almost idle when you let off the gas, hardly any compression braking unless you force a downshift by moving the gear lever to a lower gear. (one reason I HATE autos..lol)
So it might simply be a MAP issue, the engine is gonna produce more vaccume during compression braking with a manual because the weight of the vehicle is pushing the engine. You just dont get as much compression braking with a auto, so therefore not as much decel vaccume. On mine, there was a setting (cant remember where, dont have TP open right now) but it was was called something like map for mandatory DFCO, basicly (my guess anyways), when map is below that value, DFCO is forced on, reguardless of other parameters (kinda like fast PE) but I think the delay time might still apply, but not sure. Been a while since I played with it. I have mine set for 20 KPa. So any time the engine drops below map 20, dfco comes on. Stock was something like 13 (iirc, not sure) I also greatly reduced my delay time. Cant remember what it was stock, but I have it set for .5 of a second.
DE (decel enleanment) is seperate from DFCO. DE simply leans the mixture out but doesnt shut it completely off. Normal BPW for very light crusing throttle for me could be somewhere around 1.08-1.10, about the same as idle, I let off the gas and throttle is all the way closed, the bpw will drop to .49 (DE) and then 0.00 (DFCO).
It will go into DE instead of dfco when I am below 20 mph (what I have as the min speed for dfco) so when I am below 20mph, it just leans it out to .49 bpw and doesnt go into dfco. Because I have a manual, I could drive around in a parking lot in 2nd gear, let off the gas, map goes down, dfco kicked on, and back off again. Not good.

Unless I forget one, here are the following DFCO setting I have changed:
Reduced delay time. (takes less time to go into dfco)
Raised map for mandatory dfco. (raised from around 13, up to 20)
Set post dfco AE pulse if no tps increase to zero (so it doesnt jolt as bad when fuel cuts back on)
Lowered rpm to resume fueling after dfco. (from about 1400 down to 1000 rpm)
Raised min MPH for dfco. (raised to 20 mph so it doesnt come on below 20)

So far I am really happy with all my dfco settings.

**93V8S10** · 02-12-2012

Deceleration Enleanment and Deceleration Fuel Cut-Off are two different things.

**FSJ Guy** · 02-12-2012

Good point about the auto vs. manual transmission. That's probably a big part of it. I'll try raising the mandatory MAP and see what that does. But maybe it's just not meant to be used at low speeds with an automatic.

Thanks for the clarification on the DFCO versus Deceleration Enleanment. 98V8S10, you're the one who created the XDF, aren't you? EXCELLENT job!! I love all the parameter comments. They really help!