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Discussion Starter #1
All,

Has anyone had issues with the fuel cutoff on decel where it turns the fuel back on while decelerating after the rpms drop below 2000 rpm? If I monitor my PI corrections, they sit between .95 and 1.05 nearly all the time. When decelerating, fuel cuts off so no PI correction. If I tip back in before the rpm drops below 2000 rpm, all is good and PI corrections barely move. If I let the rpm drop below 2000 rpm (or something a little lower) the decel cut off turns itself off and my corrections often peg at 1.5. The car acts fine but eventually I get a check engine light if I do this enough times during a drive.

Just wondering if this is happening to anyone else.

Thanks,
Ed
 

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Under Fuel>Decel>a_Decel_RPM(Gear), change the number to an unattainable number like 10,000 for all the cells and that will disable the fuel cut under decel. See if that helps. My car was horrible for shutting down after a hard pull until I disabled this feature.
 

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Discussion Starter #3
Under Fuel>Decel>a_Decel_RPM(Gear), change the number to an unattainable number like 10,000 for all the cells and that will disable the fuel cut under decel. See if that helps. My car was horrible for shutting down after a hard pull until I disabled this feature.
That and the f_decel_ramp_in_pip_count(Throttle_Rate) are the only things listed under fuel decel. I looked at them, was pretty clueless as to how they work or what they do. I wish there was a list of what all the calibrations are and how they work somewhere.

I don't understand what causes the decel fuel cutoff to stop after somewhere just lower than 2000 rpm. I was hoping to drop that number to 1500 rpm or something.
 

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I don't understand what causes the decel fuel cutoff to stop after somewhere just lower than 2000 rpm. I was hoping to drop that number to 1500 rpm or something.
It depends on which strategy version you're running. For all of them, the Decel RPM (Gear) plays a role, but exactly how is different. In the oldest version, the value you put in here simply was the point where decel fuel cut would be turned on and off. So, if you had say 2000s in the table, decel fuel cut would be on at any rpm over 2000 and off at any value under. In newer versions, it takes the value you have in the table and adds it to your base idle speed and then does a few other tweaks depending on version (like also adding the Hysteresis value). In all honesty it's not worth getting into the fine details. Suffice it to say that if you have 800s in the table and a base idle of 900, your decel fuel cut will flip on and off around 1800 rpm.

Long story short, that's why you're seeing the fuel come back in when you get under 2000. Like Helomech74 mentioned, you could just totally disable the feature by jacking the numbers way up to something like 10000. Alternatively, to do what you said you wanted to try to get the fuel to come back in at a lower rpm, you'd lower your numbers a little. For example, if your table has 800s in it now, you could drop them all to 700s or 600s. However, you may find that you'll start to experience some stalling issues if you do that. I'd say it depends on the car.

Editing to add: I had another thought here. The fact that your corrections are pegging when the fuel comes back in under 2000 and you're off the throttle might be suggestive of a vacuum leak. Unmetered air getting sucked in somewhere while there is high manifold vacuum is gonna throw the corrections up in the direction you're seeing. If you step into the throttle to end the decel fuel cut, then you won't really experience the corrections because you won't have as much vacuum to suck in unmetered air, plus with the throttle at least partially open, the percentage of air entering the engine that is unmetered becomes less. What are you're corrections at idle?
 

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Discussion Starter #5
It depends on which strategy version you're running. For all of them, the Decel RPM (Gear) plays a role, but exactly how is different. In the oldest version, the value you put in here simply was the point where decel fuel cut would be turned on and off. So, if you had say 2000s in the table, decel fuel cut would be on at any rpm over 2000 and off at any value under. In newer versions, it takes the value you have in the table and adds it to your base idle speed and then does a few other tweaks depending on version (like also adding the Hysteresis value). In all honesty it's not worth getting into the fine details. Suffice it to say that if you have 800s in the table and a base idle of 900, your decel fuel cut will flip on and off around 1800 rpm.



Long story short, that's why you're seeing the fuel come back in when you get under 2000. Like Helomech74 mentioned, you could just totally disable the feature by jacking the numbers way up to something like 10000. Alternatively, to do what you said you wanted to try to get the fuel to come back in at a lower rpm, you'd lower your numbers a little. For example, if your table has 800s in it now, you could drop them all to 700s or 600s. However, you may find that you'll start to experience some stalling issues if you do that. I'd say it depends on the car.



Editing to add: I had another thought here. The fact that your corrections are pegging when the fuel comes back in under 2000 and you're off the throttle might be suggestive of a vacuum leak. Unmetered air getting sucked in somewhere while there is high manifold vacuum is gonna throw the corrections up in the direction you're seeing. If you step into the throttle to end the decel fuel cut, then you won't really experience the corrections because you won't have as much vacuum to suck in unmetered air, plus with the throttle at least partially open, the percentage of air entering the engine that is unmetered becomes less. What are you're corrections at idle?


At idle my corrections sit around .99 to 1.01.


Sent from my iPhone using Tapatalk
 

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At idle my corrections sit around .99 to 1.01.
Sent from my iPhone using Tapatalk
I'm assuming you're looking at Variables-Fuel-Closed Loop-Bank 1-Bank1_UEGO_PI_Correction in the old calibration tool. If you are then it's not a vacuum leak.

Thanks
Michael Plummer
 

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That and the f_decel_ramp_in_pip_count(Throttle_Rate) are the only things listed under fuel decel. I looked at them, was pretty clueless as to how they work or what they do.
Notes, I made when I first got the Pro-M EFI when I started to use the decel function. These are the parameters listed under Configuration.

s_Decel_Hysteresis: The number in this parameter represents the difference, in RPMs, between the RPM values entered in the “Decel RPM” table, and when decel fuel mode actually occurs. EXAMPLE: If the Decel RPM is set to 2000, the decel mode will take place at 1900, and will be terminated at 2100. This allows a buffer between the two so the transition is less abrupt.

s_Decel_Min_ECT: This is the minimum coolant temperature required to enter decel mode.

s_Decel_Min_Time_At_Running: This is the minimum time (in seconds) that the engine must be running to enter decel mode.

s_Off_Idle_Decel_Min_Time : This is the minimum time that the engine must be above idle to enter decel mode.

s_Decel_ Ramp_In_PIP_Count: The amount of PIP counts it will take to “Ramp In” the fuel injectors. Decel Mode works by cutting the fuel injectors one at a time in the sequence of the firing order, and bringing them back in the sequence of the firing order. The higher this number, the more gradual the ramp in will be, and the less abrupt it is. If this number is too high, there will be too much delay, resulting in hesitation when you stomp on the throttle after a decel.

s_Decel_ Ramp_Out_PIP_Count: The amount of PIP counts it will take to “Ramp Out” the fuel injectors. Decel Mode works by cutting the fuel injectors one at a time in the sequence of the firing order, and bringing them back in the sequence of the firing order. The higher this number, the more gradual the ramp out will be, and the less abrupt it is.

Ramp In: Stepping on the gas pedal
Ramp Out: Letting off the gas pedal


I hope this helps
Michael Plummer
 

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Discussion Starter #8
Thanks for the answers. At least I now understand how these decel settings work. I will investigate the possibility of a vacuum leak downstream of my throttle body. My corrections are very small at idle and normal driving around never really get past .95 to 1.05 on either bank 1 or 2. I did, however, need to put my low slope at 60 (60 lb/hr injectors) which is higher than the recommended 63 for my injectors. I wonder if doing that has masked a slight vacuum leak at idle that is more pronounced when in decel mode and a higher vacuum level. It will me a small one I suspect, might have to go somewhere and get a smoke test done.
 

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Discussion Starter #11
Notes, I made when I first got the Pro-M EFI when I started to use the decel function. These are the parameters listed under Configuration.

s_Decel_Hysteresis: The number in this parameter represents the difference, in RPMs, between the RPM values entered in the “Decel RPM” table, and when decel fuel mode actually occurs. EXAMPLE: If the Decel RPM is set to 2000, the decel mode will take place at 1900, and will be terminated at 2100. This allows a buffer between the two so the transition is less abrupt.

s_Decel_Min_ECT: This is the minimum coolant temperature required to enter decel mode.

s_Decel_Min_Time_At_Running: This is the minimum time (in seconds) that the engine must be running to enter decel mode.

s_Off_Idle_Decel_Min_Time : This is the minimum time that the engine must be above idle to enter decel mode.

s_Decel_ Ramp_In_PIP_Count: The amount of PIP counts it will take to “Ramp In” the fuel injectors. Decel Mode works by cutting the fuel injectors one at a time in the sequence of the firing order, and bringing them back in the sequence of the firing order. The higher this number, the more gradual the ramp in will be, and the less abrupt it is. If this number is too high, there will be too much delay, resulting in hesitation when you stomp on the throttle after a decel.

s_Decel_ Ramp_Out_PIP_Count: The amount of PIP counts it will take to “Ramp Out” the fuel injectors. Decel Mode works by cutting the fuel injectors one at a time in the sequence of the firing order, and bringing them back in the sequence of the firing order. The higher this number, the more gradual the ramp out will be, and the less abrupt it is.

Ramp In: Stepping on the gas pedal
Ramp Out: Letting off the gas pedal


I hope this helps
Michael Plummer
Do you have a comprehensive list of all the parameters used by the Pro-M software? It would make a great sticky on this forum if you did.
 

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I'm thinking about this on a lot of levels here now. So you say with decel fuel cut on you would see the corrections peg at 1.5 once the fuel comes back in. For how long? Am I correct in believing that during this time with the fuel back on you also see 22.4 on the wideband gauges? I know they will definitely say that during the fuel cut. I want to know if they continue to say that once injectors are firing. If you log it, are you seeing desired lambda of approximately 1 but an actual lambda of approximately 1.48?
 

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Discussion Starter #13
I'm thinking about this on a lot of levels here now. So you say with decel fuel cut on you would see the corrections peg at 1.5 once the fuel comes back in. For how long?
Maybe 2 or 3 seconds.


Am I correct in believing that during this time with the fuel back on you also see 22.4 on the wideband gauges?
No, it was usually around 16:1


If you log it, are you seeing desired lambda of approximately 1 but an actual lambda of approximately 1.48?
I will have to log it or check for logs I already have.
 

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John Janek: Am I correct in believing that during this time with the fuel back on you also see 22.4 on the wideband gauges?
EDS_5_OH: No, it was usually around 16:1

16:1 is interesting because I always saw 22.4 A/F ratio. At RPM did you have it set for?

Thanks
Michael Plummer
 

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Discussion Starter #16
John Janek: Am I correct in believing that during this time with the fuel back on you also see 22.4 on the wideband gauges?
EDS_5_OH: No, it was usually around 16:1

16:1 is interesting because I always saw 22.4 A/F ratio. At RPM did you have it set for?

Thanks
Michael Plummer
It was about 1800 rpm (800's in the decel cutoff table) and a base idle of 900 rpm. Once I dropped below that threshold, it seemed to me that the ECU was trying to achieve 14.7 and was pegging the fuel corrections trying to do so for a few seconds.
 

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Micheal, I think EDS_5_OH is saying that he saw 22.4 while in fuel cut (which is to be expected) and the 16 when the injectors kick back in rather than instantly seeing mid 14s. And to get the 16:1, the corrections are pegged adding 50% more fuel.
 
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