Need help with DFCO decel
You don't want to prevent DFCO. That is not a good move. That just covers up a tuning issue that needs addressed. It improves fuel economy and emissions. No down side at all. There is no valid reason to disable DFCO. No knowelagble tuner would ever do that. I've undone at least five this year tuned at a shop about 100 miles from here. All were mostly stock vehicles that lost mileage, and some had a slight surge when first coming to a stock. There is no upside to that.
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From: Northwest AR
I agree, I did not mean to imply I was intentionally locking it out. The point of this thread was to figure out how to make it work properly rather than jumping back and forth on the highway or simply disabling it.
I just meant when I put the truck MAP table in, it stopped doing that so following your advice of adjusting the MAP table to accommodate values a cammed car will see should put me back on the right track.
I just meant when I put the truck MAP table in, it stopped doing that so following your advice of adjusting the MAP table to accommodate values a cammed car will see should put me back on the right track.
Every calibration I have seen , from the factory the MPH thresholds are set way too low to go into DFCO at highway speeds. Guys here seem to think when they see their timing fall way off that is DFCO. That is not the case. I can't think of a stock cal I have looked at that allows DFCO above 35 MPH.
What was happening to make you think it was going into DCFO?
I have raised the MPH thresholds to allow DFCO at 55 MPH before to stop popping on deceleration. Flowmaster mufflers seem to be the worst offenders there. Besides sounding like crap. LOL
I have raised the MPH thresholds to allow DFCO at 55 MPH before to stop popping on deceleration. Flowmaster mufflers seem to be the worst offenders there. Besides sounding like crap. LOL
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From: Northwest AR
When cruising along on the interstate and I would lift throttle you could feel the converter unlock then a second or 2 later the car would go from a very free feeling coast to heavy engine braking. During this time the spark advance drops and rpms would fall from 2200+ to 1200 or so rpm.
A second or 2 later RPM would rise again, timing comes back to high 30s-40*, and the car would coast again rather than decelerate.
The latest tune revision I adjusted table B3316 from where it was in the tune posted above to 1%. I also copied the DFCO MAP activation table from my 99 Silverado since it was quite a bit different. I made no other changes I can recall. Now when I let off the throttle the car simply coasts, the obvious heavy engine braking is no happening.
A second or 2 later RPM would rise again, timing comes back to high 30s-40*, and the car would coast again rather than decelerate.
The latest tune revision I adjusted table B3316 from where it was in the tune posted above to 1%. I also copied the DFCO MAP activation table from my 99 Silverado since it was quite a bit different. I made no other changes I can recall. Now when I let off the throttle the car simply coasts, the obvious heavy engine braking is no happening.
DFCO also has nothing to do with the TCC. Coasting or "gearing down" is a function of the TCC. Staying unlocked or not when coasting. There is a binary switch to select (or not) TCC unlock on deceleration. A good scan tool will tell you if/when it actually goes into DFCO. The software I use does not use those numbers. Those tables all have names. I don't know which one you are talking about.
Btw, you can not feel it go into DFCO. You are feeling something else.
Btw, you can not feel it go into DFCO. You are feeling something else.
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From: Northwest AR
I don't recall the exact name of the table but it is the throttle percentage minimum to allow DFCO to engage.
If you can't feel it engage then you must be right that it is something else. Now I just need to figure out what. I suppose it could be a matter of something causing the idle to hang and when idle drops it is enough to let the engine brake the car?
I might see if I can do a log while monitoring every item I can find that adjusts airflow and another log watching for anything that adjusts timing and see if something jumps out at me?
If you can't feel it engage then you must be right that it is something else. Now I just need to figure out what. I suppose it could be a matter of something causing the idle to hang and when idle drops it is enough to let the engine brake the car?
I might see if I can do a log while monitoring every item I can find that adjusts airflow and another log watching for anything that adjusts timing and see if something jumps out at me?
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From: Northwest AR
EFI Live has a table for MAP activation/deactivation it has 6 or 8 cells for each based on my poor memory lol. I think there is a different place where there are a min and max cell too.
Drove the car a decent bit on Saturday morning and it was driving great all day. The only complaint I had all day was the high idle on warm restart. The rolling idle and interstate driving was perfect.
I am going to have the rockers off sometime this week to do valvesprings and I am going to see if I can do a ghetto smoke test by blowing hookah smoke into a vacuum port with the tb taped closed and see if I might have a vacuum leak between the upper and lower Fast shell (or somewhere else for that matter) before I continue with TB modification or more air tuning.
Drove the car a decent bit on Saturday morning and it was driving great all day. The only complaint I had all day was the high idle on warm restart. The rolling idle and interstate driving was perfect.
I am going to have the rockers off sometime this week to do valvesprings and I am going to see if I can do a ghetto smoke test by blowing hookah smoke into a vacuum port with the tb taped closed and see if I might have a vacuum leak between the upper and lower Fast shell (or somewhere else for that matter) before I continue with TB modification or more air tuning.
I did one yesterday that Decel Spark went to zero. Most I have noticed used 10 degrees. I would watch my MAP on decel, then put my DFCO min & max MAP around that, then that DFCO MAP vs MPH table to keep it in DFCO. Camshaft changes raises MAP values. It saves fuel and lowers Hydrocarbon emissions on decel. If your software does not have the min & max MAP constant, besides the MPH table you may not be able to make it stay in with a modified engine. Usually raising the max value 10 KPA will do it.
Have you looked at your TCC tables? Check the lock & unlock MPH at zero TPS.
Have you looked at your TCC tables? Check the lock & unlock MPH at zero TPS.
Teching In
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Have to disagree! Can feel mine... now if it's Decel Enleanment this may be true.
Of course it goes lean. That is the whole point. That is the "fuel cut off" part. LOL
Disabling that is just ignorant. No valid reason to do that at all. Why would you want to **** fuel out the tail pipe when slowing down?
DFCO is not related to the TCC unlocking, or not. That is in the zero TPS line in the TCC control tables. Some calibrations leave it locked until a low MPH, some unlock it when the throttle shuts.
Disabling that is just ignorant. No valid reason to do that at all. Why would you want to **** fuel out the tail pipe when slowing down?
DFCO is not related to the TCC unlocking, or not. That is in the zero TPS line in the TCC control tables. Some calibrations leave it locked until a low MPH, some unlock it when the throttle shuts.
Teching In
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Was just giving an example of how he could see DFCO by AFR if he had a WB...
Before DFCO is entered there is a Deceleration Enleanment.
"This calibration increases or decreases the decel fuel cutoff air value when decel fuel cutoff is entered."
It's a short period but two different things. You would not feel the Decel Enlean portion.
Im not sure who recommended turning DFCO off? Was not me...
Also not sure who said TCC was a part of DFCO operation? Was not me. But what he describes about TCC unlock and then DFCO is exactly what you feel when it is happening. Again two different things. When you let off throttle TCC will unlock then DFCO parameters have to qualify to enter DFCO.
The calibration I'm looking at for MPH qualifier is over 15 MPH, but other qualifiers can't be met to enter DFCO until hard deceleration, like 70 MPH and let off throttle would qualify MAP parameters, but not 40 MPH and let off throttle. Still takes a few seconds to enter.
Both Low TPS and High TPS DFCO Spark Advance are the same in this calibration and show 0* at 2000 RPM and even lower under 2000 RPM.
So it seems DFCO is working properly. Yes you can feel the engine braking when DFCO is active.
So back to his original issue with TB?
Before DFCO is entered there is a Deceleration Enleanment.
"This calibration increases or decreases the decel fuel cutoff air value when decel fuel cutoff is entered."
It's a short period but two different things. You would not feel the Decel Enlean portion.
Im not sure who recommended turning DFCO off? Was not me...
Also not sure who said TCC was a part of DFCO operation? Was not me. But what he describes about TCC unlock and then DFCO is exactly what you feel when it is happening. Again two different things. When you let off throttle TCC will unlock then DFCO parameters have to qualify to enter DFCO.
The calibration I'm looking at for MPH qualifier is over 15 MPH, but other qualifiers can't be met to enter DFCO until hard deceleration, like 70 MPH and let off throttle would qualify MAP parameters, but not 40 MPH and let off throttle. Still takes a few seconds to enter.
Both Low TPS and High TPS DFCO Spark Advance are the same in this calibration and show 0* at 2000 RPM and even lower under 2000 RPM.
So it seems DFCO is working properly. Yes you can feel the engine braking when DFCO is active.
So back to his original issue with TB?
The engine braking feel is more pronounced when the TCC is locked on decel. Some calibrations leave it locked on decel, some unlock it.
About not disabling DFCO, some mentioned changing the MAP valued, and it not going into DFCO. I was addressing him, not you.
About not disabling DFCO, some mentioned changing the MAP valued, and it not going into DFCO. I was addressing him, not you.
