DFCO stopped working

[str8dum1]

Hey guys,

2018 silverado L83 A8.

Can someone look over this tune and see why DFCO is not engaging when I let off the gas? I should be exceeding all the DFCO criteria. Are there other criteria needed to go into DFCO?

Whenever I take the foot of the gas, instead of DFCO, it pegs the wideband full rich and the IPW stays at like 1.x. It will go into DFCO very randomly and I will get the proper full lean, 0 IPW, and instant mpg goes to 99.

I also added a log where it you can see 0 APP but fuel stays on making the wideband go full rich.

I can add any additional info as needed. Its driving me crazy just dumping fuel everytime I coast down.

[Craig18SSA8]

I have this same issue, hopefully someone can chime in on this.

[TriPinTaZ]

What mods do you have?

[str8dum1]

just headers, lt4 fuel - intank 450, and a eforce 2300

[TriPinTaZ]

lol just....

Try increasing this to 100lb ft or more.

Fuel > Cutoff/DFCO > Torque > Enbl ZP Imm Delta


You may need to fine tune it for your torque model. But essentially from my experience, this value is what allows the car to enter DFCO when you let off the throttle. It references Driver Requested Immediate Axle Torque and Zero Pedal Driver Torque. Monitor those PIDs in the scanner and look at the value when you let off the throttle. There is a good chance this value isn't consistently going low enough for DFCO. The sum of Driver Requested Immediate Axle Torque and Corrected Zero Pedal Driver Torque must be below 7.38 ft lbs in your tune. Just as a reference, LT4's have this value around 40 ft lb on the OEM tune. Also, if you're going in and out of DFCO with no throttle input you may need to raise its opposite table that is below it "Dsbl ZP Drvr Delta". This basically is the requested driver torque value (gas pedal press) that the ECU needs to see before it disables DFCO.

Don't skew that table too much or you could have adverse drive-ability. You may need to play around with it. On one car I just added 40ft lb to each table and it was great. On another car I only added 30 ft lb to the disable table but 100 to the enable. You gotta play around with it.

[str8dum1]

thanks for the advice, I will test it out!

[str8dum1]

no dice, didnt work. Injectors still staying on when foot take foot off pedal. arghhh...

Not sure what else to check...

[Craig18SSA8]

Yeah, same here. Tried several different settings. It basically just enables or disables the dfco. Didn't effect what happens when it enables or disables.

It's a bit frustrating as it really makes stop and go traffic a little bit uncomfortable. It spikes rich sometimes so bad it wants to hydrolock. Occasionally, it just stays pinned. I shift into neutral and it jumps back to stoich. Most times I come up to a stop dfco enables during the primary decel but once I get below 40mph on the brakes it disables and is pegged rich. Also happens when dfco enables during any point in driving. Let go of the pedal, most of the time it goes rich, stays rich until I tap the gas for a split second then dfco enables. Then when I get back on the gas it goes %30 rich for 5 seconds or so as it trims back to stoich. The low end fueling is perfect on VVE and the MAF. There has to be some specific changes that need to be made somewhere. Transient fueling?

I pulled fuel from those areas in VVE and had no luck and a worse problem, that went back to stock. I believe this is also related to losing the deceleration pops as it is not engaging properly. The torque values really only seem to effect when or if it is engaged or disengages.

[TriPinTaZ]

Minimum Spark inadvertently plays a role in DFCO entry because it alters the calculated torque value so lowering the minimum spark in decel may or may not have a positive effect. The Enable ZP and Disable ZP is a range for DFCO entry and exit. If your calculated torque changes too much then this will be out of range and you may have to increase both Enable and Disable by the same amount to get it back inline with what torque is being reported when you let off the throttle.

To be honest the DFCO is a PITA on the Gen V as it looks to be totally torque driven. I also wonder if there are any tables we are missing that would help. I've seen NA cars with added superchargers have issues with DFCO and I've seen LT4's with 95mm or larger TB's added have issues with DFCO delays. I have not found a solution but have found that keeping the torque model lined up as close to stock as possible down low definitely helps.


Try raising both values by 10 or 20 at a time to see if you find the sweet spot for DFCO entry/exit.

[humandm]

I had this same problem on a C7 A8. Fix was to set Enable VSS to 255 and Disable VSS to 256 under Fuel, Oxygen Sensors, LTFT Idle Cells Thresholds.

[Jeff7577]

Your torque converter is locked up.

DFCO Enable RPM TCC Unlock 1200 rpm

5th gear TCC apply at 0% Throttle is 21 mph

[humandm]

I had this same problem on a C7 A8. Fix was to set Enable VSS to 255 and Disable VSS to 256 under Fuel, Oxygen Sensors, LTFT Idle Cells Thresholds.

To be clear...this fixed both the richness when DFCO was not active and allowed predictable DFCO engagement which is controlled by the other parameters.

[TriPinTaZ]

I had this same problem on a C7 A8. Fix was to set Enable VSS to 255 and Disable VSS to 256 under Fuel, Oxygen Sensors, LTFT Idle Cells Thresholds.

This fixed a DFCO issue I had with another car as well. Thanks for sharing.