why should I re enable it after I tune with it off???
I dont want the exhaust popping and lean condition it creates....is there a point of why it Must be on??? or is it just a gas saver function or what??

Just trying to understand things that I dont understand yet

 

so you disabled lean cruise and popping went away on decel??

 

yes...completely....
I know that I have been told that the popping is caused when you are extremely lean...which would be deceleration fuel cut off conditions...

and I ask again....
Is there any real reason to re enable it when done tuning??? isnt it justa fuel saver???

 

Thats odd. Mine constantly goes into DFCO while coasting. its great for saving gas. In DFCO it should be getting no fuel at all so its not lean, its nothing. I wonder if something is set wrong. Sometimes it'll pop when going from dfco to fueling again.

 

The popping you hear is excess fuel lighting off in the exhaust pipes - aka raz. Maybe because your tune is right is why you don't hear it any more?

 

Just out of curiousity... Why disable DFCO when you're tuning anyway? I understand it gives a lean condition on decel, but wouldn't disabling it do the opposite and show a rich condition?

 

I'm not sure about the amount of fuel being delivered during DFCO, but I would assume the motor is getting some fuel. It's just not the same amount of fuel. If you ever watch your data in real time, it's rather interesting. When my car hits DFCO, my LTFTs drop to -2 ~ -4% (still waiting on custom tune to cure positive LTFTs), the MAP sensor drops to just about 2.2psi (idle is close to 4.Xpsi), and my spark advance is only 2-4 degrees. The pop you mention during transition from DFCO to normal conditions is a result of the MAP equalizing I believe. There's sudden pressure change (from 2.Xpsi to +5.Xpsi) when you get back on the gas and the popping is a side effect of the motor adjusting to the split-second changes. Of course, this is only a theory of mine and I have been wrong before. But, it makes sense based on the data I've seen on the Predator.

 

i get a lot more popping w/ my -1 Ltrm tune then i did w/ my +6-+10 Ltrim tune. THis i sin a vette though.

Dave

 

DFCO is NOT Lean Cruise.

Deacceleration Fuel Cut Off

From reading the HPTuners help section on DFCO (see below), you may not want this while tuning since it'll give some abnormal readings when it is on (essentially bad data).

Re-enable it when you are done tuning to save gas.

Ben





Fuel Cutoff, DFCO


The Fuel Cutoff and DFCO Tab contains parameters related to fuel cutoff and RPM limiters as well as Deceleration Fuel Cutoff parameters.


Deceleration Fuel Cutoff (DFCO)
DFCO can be broken down into 5 main modes of operation.

Qualifications to consider fuel cutoff (Enable)
Spark threshold/ ramp down values and enable Qualification hysteresis values while getting to fuel cut point. (Entering)
Spark values while in fuel cutoff (In)
Qualifications to stay in fuel cutoff (Exit)
Spark ramp up values to exit fuel cutoff (Exiting)


DFCO Qualification
DFCO must pass a series of enable tests to even be considered. If any of the tests are not passed, the DFCO process will not be started. (Fuel is still on)
Fuel Tab - DFCO Enable Normal Section:

Temp: Engine Coolant temperature must exceed this value.
Enable Speed vs. Baro: The vehicle speed must exceed this value.
RPM vs. Gear Entry: Engine RPM must exceed table value.
TPS vs. RPM: Throttle position must be below this table value.
Map vs. Baro Entry: Map must be below this table value.


Fuel Tab - DFCO Enable Clutch Transition Section: (Not used on all models)
These values over ride ANY of the DFCO Enable Normal Section qualifications (Enable, Entering, Exit) if recent clutch activity has been detected.
These values will remain active for a short time period before reverting back to the normal qualifications.


Temp: Engine Coolant temperature must exceed this value.
Speed: The vehicle speed must exceed this value.
RPM: Engine RPM must exceed table value.
TPS: Alternate VCM %Throttle position Change must be below this table value.
Map: Map must be below this table value.
TPS Hyst: Adds to Alternate VCM %Throttle position Change value.


DFCO Entry:
Enable tests passed, VCM selects spark threshold/ ramp down values and Enable Qualification hysteresis values while getting to fuel cut. (DFCO is considered active and Fuel is still on)
Spark Tab - DFCO Entry, Active, Exit Spark Section:

Entry Threshold vs. RPM: This is the degree spark advance that must be reached to turn the fuel off.
Entry Blending vs. RPM: This is the spark ramp out rate to reach the Entry Threshold vs. RPM spark value.
Spark is removed at a rate of 12.5msec at the Entry Blending multiplier value. If your current spark advance is 20 degrees @3000 rpm, your Entry threshold is 5 degrees, and your removal rate is 0.010, the VCM will remove .2 degrees (20 x 0.010) of spark every 12.5 milliseconds until the Entry Threshold of 5 degrees is reached.
Fuel Tab - DFCO Enable Normal Section:
Speed Hyst: Subtracts from Enable Speed vs. Baro table value.
RPM Hyst: Subtracts from RPM vs. Gear Entry table value.
TPS: Adds to TPS vs. RPM table value.
Map Hyst: Adds to Map vs. Baro table value.


In DFCO:
All of the qualifications have been met, Spark Cut Threshold has been reached and the fuel has been turned off. VCM sets the spark advance and looks for a reason to exit DFCO.
Spark Tab - DFCO Entry, Active, Exit Spark Section:

Active Advance vs. RPM A: This is the degree of spark advance while the fuel is turned off.
Min TPS for Table A: TPS must exceed this value to use table A.
Active Advance vs. RPM B: This is the degree of spark advance while the fuel is turned off.
Max TPS for Table B: TPS must be under this value to use table B.
Fuel Tab - DFCO Enable Normal Section:
Enable Speed vs. Baro: The vehicle speed must exceed this value.
RPM vs. Gear Exit: Engine RPM must exceed table value.
TPS vs. RPM: Throttle position must be below this table value.
Map vs. Baro Exit: Map must be below this table value.


Exiting DFCO:
VCM has found a reason to turn the fuel back on and start the spark exiting process.
Spark Tab - DFCO Entry, Active, Exit Spark Section:

Exit Blending vs. TPS: Spark is added at a rate of 12.5msec at the Exit Blending value. If your current spark advance (Main spark table, not Active Advance vs. RPM A/B) is 20 degrees @3000 rpm, and your add rate is 0.286, the VCM will add .286 degrees of spark every 12.5 milliseconds until the main spark table value is reached.
Exit Blending CT (Clutch Transition): This value over rides the Exit Blending vs. TPS table if clutch activity has been detected.
Stall RPM: This is the lower RPM limit for DFCO fuel cut.

 

When I coast in DFCO, my scanner shows my injector pulse rate at 0

 

I had the same issue with DFCO. On it creates backfires right at ~2000 rpm. Off none.

I will tune DFCO to improve once I get more critical aspects out of the way. I really like the engine braking affect, great at the track.