DFCO & DE Not Working (Deceleration Fuel Cut Off Enleanment)

Holden/Delco Tuning. ALDL, OBD 1.5. Circa 1989 to 2004.
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h4x0r
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DFCO & DE Not Working (Deceleration Fuel Cut Off Enleanment)

Post by h4x0r »

Hey guys, My tune goes rich when I back off the accelerator, low 13:1s which causes surging, especially at low rpm and speeds.

I'm using a 424 with 11p on a 304 V8. I got a new cam recently and can't figure out how to get DFCO and DE to work. I don't think I've changed anything and i've compared my settings to the stock 11p bin also.

I've tried cheating by reducing VE and timing in the cells where it goes into vacuum when i back off the accelerator but its still too rich.

In my logs the "Decel Fuel Cut" never changes to set....
status.PNG
engine.PNG
settings.PNG
What am I missing?
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antus
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Re: DFCO & DE Not Working (Deceleration Fuel Cut Off Enleanm

Post by antus »

The bottom data item is o2 sensor outside of high/low threshold. Not sure if that indicates there is also an error set, and that may effect it. Is it just that your VE table is too far out and needs tuning for the cam and that's causing other issues? If you can post a log and a bin it'd probably be more helpful than all the individual settings.
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immortality
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Re: DFCO & DE Not Working (Deceleration Fuel Cut Off Enleanm

Post by immortality »

How big is the cam, How much vacuum are you getting on decel?

Depending on the cam size you might not achieve a high enough vacuum (low kpa number) to get into DFCO. Try increasing the parameter DFCO max MAP for Automatic to a number slightly larger than the lowest kpa reading you see when closing the throttle to engine brake.
h4x0r
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Re: DFCO & DE Not Working (Deceleration Fuel Cut Off Enleanm

Post by h4x0r »

immortality wrote:How big is the cam, How much vacuum are you getting on decel?

Depending on the cam size you might not achieve a high enough vacuum (low kpa number) to get into DFCO. Try increasing the parameter DFCO max MAP for Automatic to a number slightly larger than the lowest kpa reading you see when closing the throttle to engine brake.
cam.PNG
cam.PNG (1.02 MiB) Viewed 1895 times
Only drops down to 60kpa when I back off the accelerator. The setting DFCO Max Map for Automatic ( +8 8kPa hysteresis) is set at 20kpa. Does that mean it has to be above or below 20kpa? Do I need to change that number to 60kpa?

I also experimented with Deceleration Enleanment by cranking the numbers up and only noticed some effects in higher rpm. It seems like DFCO is necessary for low rpm?
h4x0r
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Re: DFCO & DE Not Working (Deceleration Fuel Cut Off Enleanm

Post by h4x0r »

antus wrote:The bottom data item is o2 sensor outside of high/low threshold. Not sure if that indicates there is also an error set, and that may effect it. Is it just that your VE table is too far out and needs tuning for the cam and that's causing other issues? If you can post a log and a bin it'd probably be more helpful than all the individual settings.
Heres the bin. VE is a little out because I just installed a new alternator and better wiring to the injectors which appears to richen everything up with the higher voltage. Spark map is a little ugly as I try to make the CAM happy. I'm more focused on figuring out why the car is too rich when im backing off the pedal. I'm happy with accelerator enrichment and general cruising.

Is it just DFCO I need to get active?
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immortality
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Re: DFCO & DE Not Working (Deceleration Fuel Cut Off Enleanm

Post by immortality »

h4x0r wrote:
immortality wrote:How big is the cam, How much vacuum are you getting on decel?

Depending on the cam size you might not achieve a high enough vacuum (low kpa number) to get into DFCO. Try increasing the parameter DFCO max MAP for Automatic to a number slightly larger than the lowest kpa reading you see when closing the throttle to engine brake.
Only drops down to 60kpa when I back off the accelerator. The setting DFCO Max Map for Automatic ( +8 8kPa hysteresis) is set at 20kpa. Does that mean it has to be above or below 20kpa? Do I need to change that number to 60kpa?

I also experimented with Deceleration Enleanment by cranking the numbers up and only noticed some effects in higher rpm. It seems like DFCO is necessary for low rpm?
For the factory settings I believe it means it has to drop below 20kpa and will come out of DFCO when it goes above 28kpa

If yours does not drop below 60kpa then that setting will need to be 60kpa (or slightly above) but less than where it idles. I would work on idle tuning first as that isn't a lot of vacuum. Keep adding idle timing until you achieve the highest possible vacuum (lowest kpa number).
h4x0r
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Re: DFCO & DE Not Working (Deceleration Fuel Cut Off Enleanm

Post by h4x0r »


If yours does not drop below 60kpa then that setting will need to be 60kpa (or slightly above) but less than where it idles. I would work on idle tuning first as that isn't a lot of vacuum. Keep adding idle timing until you achieve the highest possible vacuum (lowest kpa number).
dfco.png
I changed mine to 60, 70 and now 90kpa and DFCO is still not working. I also tried increasing the speed to 50kph

Its just too rich at low speed on deceleration and surging bad.

Its not an open/closed loop thing? Closed Throttle VE Option = Set? ..... Sometimes tunerpro can be hard to understand all the logic envolved.
immortality
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Re: DFCO & DE Not Working (Deceleration Fuel Cut Off Enleanm

Post by immortality »

Leave everything stock except the KPA max threshold.

I'd worry about getting the VE table right before working on things like DFCO, those nice to have things once all the other shit is sorted.
h4x0r
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Re: DFCO & DE Not Working (Deceleration Fuel Cut Off Enleanm

Post by h4x0r »

OK I figured it out.... and solved a lot of issues!!!!

Basically the problem I was having was once I pulled off throttle, especially at low speed and low rpm the car would go too rich 13.1:1 and start surging bad. I Tried pulling a lot of VE out of these cells. I tried pulling a lot of timing out and also tried adding more timing (35 degrees) in these cells and it just wouldn't pull any leaner. So it had me thinking.... What if the siemens 60lb injectors can't squirt fuel any lower.. so I changed from double fire to single fire 0ms to 2ms which is where it does all idling and cruising and BAMMMM!!!! INSTANT RESULTS :cash:

The car has gone from grumpy to happy. It has smoothed out idle. Iac was always a pain in the arse to get right and now its more stable and easier to tune.

It seems like it has a larger AFR window its happy in. Before I had to really dial in 14.4 AFR to idle and cruise but now its happier in a far larger window of AFR. So im probably going to have to change a lot of my AFR cells back to 14.7

There seems to be less dead spots on throttle cracking.

It cruises so much better and with less fuel.

Changing the auto between PRND is more smoother

It has less fuel smell

By increasing the DFCO max map to 70kpa it does turn on now, but I need to point out its not very obvious to see in the "Engine Status Flag Data Only" log as it flashes a "SET" label so quickly that you can barely see it. Its more obvious to see it pull timing in the logs. Only problem is DFCO surges as you see in the log below. I'm going to leave it turned off for now. Not sure what to do about it surging or if its going to be useful anymore anyway.
dfco-graph.PNG
immortality
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Re: DFCO & DE Not Working (Deceleration Fuel Cut Off Enleanm

Post by immortality »

Yup, that will definitely do it.
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