DFCO Info

[TheApocalyptican]

Looking into adjusting the DFCO to turn on a little more often. I get the basic idea of how everything works but there are some things that are confusing. 1st off, after logging with it enabled, I saw a BPW MS drop to 0.xx at around 55mph after letting off from 70mph. I've read that the BPW MS should drop to 0 when DFCO engages. Does this 0.xx qualify for 0, or should it actually be a flat 0.00? If it doesn't qualify, is this just DE then, and not DFCO?


The other part I am confused with is why the DFCO RPM to disable, and Map to disable scalers are maxed out. RPM is at 6375 which seems to me like it would conflict with the RPM threshold table. And the Map is 99.69, which would seem to conflict with the Map threshold table.

Edit: 7747 ASDU $42

[EagleMark]

Looking into adjusting the DFCO to turn on a little more often. I get the basic idea of how everything works but there are some things that are confusing. 1st off, after logging with it enabled, I saw a BPW MS drop to 0.xx at around 55mph after letting off from 70mph. I've read that the BPW MS should drop to 0 when DFCO engages. Does this 0.xx qualify for 0, or should it actually be a flat 0.00? If it doesn't qualify, is this just DE then, and not DFCO?

Post a log so I can see it. So it actually says 0.xx? Or is XX a little number?

The other part I am confused with is why the DFCO RPM to disable, and Map to disable scalers are maxed out. RPM is at 6375 which seems to me like it would conflict with the RPM threshold table. And the Map is 99.69, which would seem to conflict with the Map threshold table.

These are some of the last things I'm working on for the next/last version. I'm not sure they are all worded correctly and none have ever had comments in XDF description.

IIRC the RPM to disable cutoff and MAP to disable cutoff should read RPM/MAP to Disable, meaning it is always on until that point.

The ones to adjust are the three tables "DFCO - Upper/Lower RPM/MAP/MPH Threshold"

You seemed to have found one of the last things I haven't tweaked to death and fully understand in $42!

[TheApocalyptican]

The 0.xx were small numbers. They were in the 0.90's, 0.80's, or it seemed to bottom out at 0.40 It only seemed to be doing it from higher speed decel's, not medium speed ones. Log is kinda long, as I was just kinda checking everything out. Still gotta do more VE tuning. The 70mph decel is just under 30 mins in. While you're looking...do the vac/map readings seem low/high to you? Seems to me like they are more where I'd expect them early on, and drop after being warm for a while.

[EagleMark]

I'm not sure that is DFCO and maybe just Decel. You can see the Async fueling flag come on when this happens.

Not much idle time at end of log, always leave some in drive and park time at end of log, it helps. Like for instance best I can tell at idle your TPS voltage is .98 IAC counts were 10 and idle was 1100, so not so good. During that DFCO/Decel TPS voltage was also .98. Should be closer to .54, so either the throttle blade adjustment is way off or throttle is sticking open?

I have to do a lot more work in testing and going through dis-assembly to get the description right for all the DFCO settings, not going to happen soon but on my list.

[TheApocalyptican]

Async comes in during DE, or DFCO? Wasn't clear to me which you meant.
.98 is currently where the tps sits. 0.98 is a little high. IAC was dropping to 0, so I just went thru the iac reset again with a helper, and dropped it about 3/8 to 1/2 turn, so the tps should be lower now. I've never been able to get it to adjust all the way to .54. Need to get some kind of dremel bit or something in order oval out the tps holes and adjust. I haven't been to worried about it due to reading that the tps is looked at when started, and that the reading is considered 0%.

The RPM/Map to disable being the way you said is kind out what I figured. It was just the wording of the scaler that was messing with me.

On a completely separate thing I've been curious about, how does the ECM know how much fuel to command when in open loop for any reason? I get that it is based on an AFR table, but I didn't think the o2 is read in open loop, so how does it calculate how much fuel is needed?

[EagleMark]

Async comes in during DE, or DFCO? Wasn't clear to me which you meant.

I think Decel, not really sure about DFCO if it's even working, like I said you got me on one I have not worked on heavily. SO take it with a grain of salt, may be another internet rumor by the time I'm done figuring it out for certain?

.98 is currently where the tps sits. 0.98 is a little high. IAC was dropping to 0, so I just went thru the iac reset again with a helper, and dropped it about 3/8 to 1/2 turn, so the tps should be lower now.

Check at end of a drive to see where IAC counts are. Get a log of idle at end of log, seems to high, something is wrong or not set right?

On a completely separate thing I've been curious about, how does the ECM know how much fuel to command when in open loop for any reason? I get that it is based on an AFR table, but I didn't think the o2 is read in open loop, so how does it calculate how much fuel is needed?

"Open Loop - AFR vs Temp" is the starting point for Open Loop fueling.

Your other question of low vacuum?High MAP? Seems it is even at highway speeds? Have you set base timing to 0? Any vacuum leaks? Seems like a possibility with the high idle as well?

Start a log when fully warmed up, drive steady throttle position, 10% 20% etc, one WOT run and let it idle at end of drive in gear a minute and in park a minute. With that I may be able to help you out.

[TheApocalyptican]

I even tried searching other sites that usually have tuning info...and wasn't able to find very much on DFCO. I'll mod the tps to.54 and post up a log like you said. Timing is 4 btdc and tune is set for it at 4. No vac leaks. My biggest concern with the vac would be that the engine itself is no longer up to snuff. I know afr vs temp is where it starts. What I'm wondering is how it knows afr without reading o2. Is there some kind of calculation done based on the bpw and something else?

[chevmasta]

I would really like to know more DFCO info also. Is there any pointers as to what maps to adjust to get it to turn on more often? Like....most of the times I back off the gas. I haul loads.....so I want it on ALOT.

[TheApocalyptican]

Reducing the enable timer could get it into DFCO quicker. I also know that the Upper/Lower RPM, MAP, & MPH are pretty much set right already. Changing them isn't going to do much. These tables are set up so that if you are above the upper, it can engage all the way thru to the lower, and when it gets to the lower it disengages. Then, it can't come back on again until you are above the upper again. Also, all three need to be above. If only 1, or 2 are above, it won't engage.

[chevmasta]

Reducing the enable timer could get it into DFCO quicker. I also know that the Upper/Lower RPM, MAP, & MPH are pretty much set right already. Changing them isn't going to do much. These tables are set up so that if you are above the upper, it can engage all the way thru to the lower, and when it gets to the lower it disengages. Then, it can't come back on again until you are above the upper again. Also, all three need to be above. If only 1, or 2 are above, it won't engage.

My delay timer is at 1 sec.

These are the only 3 maps in my .xdf
What would you recommend changing?

[TheApocalyptican]

The delay timer is the only one that I can see doing too much, but at 1 sec, you're not gonna get much change. Whats odd(compared to my $42) is that your hi in the MAP is lower than the lo. According to what I read from RBob at 3rd gen, anytime it's above 16.47(I think it says 16, can't tell for sure from the picture) it can enable the DFCO. However, when it drops to 33.97, or below, it exits DFCO. With it set this way, when you first let off the throttle, it'll engage DFCO, but after not too much longer it's going to come back out, as you should be able to get below 33.97 pretty easily. I'd wait for either EagleMark to confirm this, or wait till I read more, and/or experiment with my truck before changing yours. It's up to you weather you want to experiment on your own or not.



EagleMark: Not sure if any of this will help you as far as DFCO decoding but...So far, according to what I am reading over at 3rd gen, my 70mph decel is NOT DFCO. The bpw ms should be 0.0. Whether this means it can be 0.09-0.01, or if it has to be 0.00 I'm not sure. Also, the o2 mv should drop to something like 0.004. While this is all from a aujp bin, mine has to be somewhat similar. Also, in the aujp, the spark advance drops to 0.0. Not sure if mine should be the same. Also, looking thru my previous logs, when I am using my VE tuning bin that has the DFCO disabled, I was still getting the numbers that we talked about above, which pretty much confirms that DFCO is not coming in during the log I posted.

[EagleMark]

Darn you guys with stuff I haven't figured out!

And I still have a lot to learn about following code...

Now I have to cancel tomorrow and drive around all day testing this!

Looks like it only works between those RPM, MAP and MPH settings?

 					; Limits for FUEL CUT OFF In decel
						;
						;	  1000/1400 RPM
						;		  15/18 MPH
						;
						; 4 LINE TBL
						;---------------------------------------------
LD8E2   LDX     #$D2E3	; POINT TO 4 LINE TBL
						;
        LDAB    $0008	;
        BITB    #$08	; BIT 3,
        BEQ     LD8EC	; BR IF NOT B3,
        INX     		;
LD8EC   LDAA    $001C  	; RPM/25
        CMPA    0,X		; 1000/1400 RPM HYST
        BLS     LD8B5	; BR IF RPM LT 1000/1500, (EXIT FUEL C/O)
        LDAA    L0034  	; MPH/1
        CMPA    2,X		; 15/18 MPH
        BCS     LD8B5	; BR IF Vss LT 15/18 MPH, (EXIT FUEL C/O)
						;							;
						; CK DECEL FUEL C/O TMR		;
						;							;		
        LDAA    L00A1	; DECEL FUEL C/O TMR
        BNE     LD934	; BR IF Non Z
        LDAB    >$D2EF 	; 3 Sec's MIN BETWEEN DECEL FUEL C/O
						;
        LDAA    $0003	;
        BITA    #$10	; b4, (IN FUEL C/O)
        BEQ     LD90B	; BR IF NOT b4
        ANDA    #$EF	; CLR b4
        STAA    $0003	;
						;
        STAB    L009F	; BETWEEN DECEL FUEL C/0 TIMER
LD90B   CMPB    L009F	; BETWEEN DECEL FUEL C/0 TIMER
        BLS     LD914	;
        INC     L009F	; INCR DECEL FUEL C/0 TIMER
        BRA     LD946	;
						;---------------------------------------------

[TheApocalyptican]

After looking everything over, and looking elsewhere on the net....it appears that the only thing that might be holding me personally back from being able to enter DFCO is the NON .54 tps. The setting is 1.57%. Technically from what I have read, the ecm should see my .98 as being 0 and thus it should kick the DFCO in, but maybe it's not?

According to the pdf available her, the RPM to disable is actually a differential that if for example the rpm is 7000, then the rpm would have to drop by 6375 rpm to 625 in order to disable DFCO. The MAP is the same, it's a differential that if for example the map is at 100, and there is a 99.6 kpa difference, it will not engage the DFCO. Basically with the stock settings, these will NOT prevent DFCO under any real circumstance.


Went out and logged. I've got a miss that has showed up after checking and regapping the plugs, so I need to pull em back out again. After I fix this, I'll upload a log to see what you think of the vac. As far as the DFCO.....according to what I've read of how it works, mine is NOT coming in at any point. I've got the tps at .55 now, and with everything set up the way it seems it should be to work and when in the area where the DFCO should occur, it's not. I get a much lower pw ms, but never actually cuts out completely like it should. I wish I had an emulator, as testing this would be so much easier.

EagleMark: Take your time, and get to the DFCO when you can. Only thing I ask is that you post back in this thread when you are able to sort it out.


More info: I decided to try out tunercat. In tunerpro the Lower MAP threshold matches the DFCO Enable map in tunercat. Tunerpro has the "number" as 20 kpa whereas tunercat has it at 10.4. The Upper thresh in tuner pro is 40.0 and in tunercat it is listed as DFCO disable MAP with a value of 34.0.

[EagleMark]

According to the pdf available her, the RPM to disable is actually a differential that if for example the rpm is 7000, then the rpm would have to drop by 6375 rpm to 625 in order to disable DFCO. The MAP is the same, it's a differential that if for example the map is at 100, and there is a 99.6 kpa difference, it will not engage the DFCO. Basically with the stock settings, these will NOT prevent DFCO under any real circumstance.

Where's that PDF? I'd like to read it. Don't think they are a differential/Hysterus/Delta, I think they are actual disable numbers in testing last night...

More info: I decided to try out tunercat. In tunerpro the Lower MAP threshold matches the DFCO Enable map in tunercat. Tunerpro has the "number" as 20 kpa whereas tunercat has it at 10.4. The Upper thresh in tuner pro is 40.0 and in tunercat it is listed as DFCO disable MAP with a value of 34.0.

There's always an issue of differant numbers from one bin definition editor to the next, usually TunerCat is accurate as all the defs are written by a Professional, sometimes I have seen them different as well, could use different conversions like 10.2% is same as .102 etc... Point is what you see whether its 5 or 9, lowering or raising is going to work.

Here's what the disassembly says, it to could be commented in accurate. Bin is hex, number 8 and 64 are decimal equivalent, then the conversion in TP or TC makes it a real world number like MAP kpa in this case.

 					;
LD2E7   FCB  8      ; 13.3 Kpa, DECEL FUEL Cut Off MAP Thresh, Lower     
LD2E8   FCB  64     ; 34.0 Kpa, DECEL FUEL Cut Off MAP Thresh, Upper 
          			;

[EagleMark]

Here's what I found to enter DFCO.

DFCO CTS to enable = engine has to be above this temp.
DFCO MAP Disable and DFCO RPM disable. I believe they are just that, anything over and DFCO is disabled. So in this case they are wide open.
DFCO TPS has to be below this vaule to start DFCO. This is ECM calculation of TPS% not the calculated from voltage value in ADX file which is close, not accurate, there is no TPS% in this datastream.
I changed the titles of Upper and Lower to Enter and Exit because that is how they work.
DFCO Enter ~ Exit RPM/MAP/MPH All three be above Enter, then there is still a 2 second delay. It will stay in DFCO until any one of the three hit Exit.

Your log was same as mine and went Async and BPW went to .40. It's in DFCO! I tried to make it change lower or higher and can't be done when Async and in DFCO. Remember this is a hack of data stream from 4bytes/32bit, not a factory ALDL data, so something could be off a little? I did some testing and it is not Decel Enlean! Also turned off DFCO by rasing enble temp and BPW was much higher so we know it's working.

It is hard to get into DFCO while on freeway in OD cruising and then let off, just does not meet all three MAP/MPH/RPM qualifiers, MAP I beleive at that point. But if you run highway speed in D and let off it comes on big time and stays on till one of the three Exits are hit. Man it slows you down too! WOuld help for braking but not much help for coasting.

Good subject your brought up! It forced me to finish this folder of DFCO Parameters. I only need to get some temp conversions figured out that the team is all helping me with in another thread in GearHead section. When it's done I'll release $42-1227747-V6.xdf Final Addition! Has a lot more notes in all comment sections as well as some new features of TunerPro Patches.