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Thread: Soften deceleration fuel cut on low RPMs

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Posts: 21-30 of 44
2013-07-24 22:57:33
#21
Originally Posted by JKTUNING
Originally Posted by Evlnxr
Fuel Cut tables have always baffled me, the description in help says a lot of stuff, but not what changing things higher or lower rpm, and/or making the rpm values closer or further apart will change the driving experiance.

I recently picked up a GTIR Pulsar, with totally stock ecu, and its a joy to drive compare to my P10, it starts and idles perfectly, can be driven at light load low speed easily, has rock steady idle all the time. My P10 is a pig in traffic, and idles horribly at times. Yeah the P10 with the tuned ecu is faster and fine under load, the the light load and idle stuff is baffling and so hard to work out what and where needs to be adjusted to sort these issues out.


I think that you will find that the majority of the idle problems that customers have are tied to mechanical issues.

The idle and light load is ALWAYS the hardest part of the tune to dial in and get just right, but anything like a MAF leak or vac leak at the IM will cause all kinds of problems.

To the OP, if you car is literally stalling after over run fuel cut .. it is HIGHLY likely that you idle air valve is not opened far enough to catch the idle OR that section of the fuel/ignition map needs some adjustment.

A lot of people also make the mistake of thinking that they can idle larger injectors (earlier style) at the same AFR as smaller stock injectors. This can definitely cause an erratic idle, try adding a little fuel to the idle portion of the map or even adjusting your battery offset tables.

I do understand that the idle and fuel cut parameters can be a little overwhelming when you first look at them.

But if you take the time and really read how it all works together and adjust 1 thing at a time to see a trial and error you might get the hang of things.

Also, if you guys have some more specific questions, other than this stuff baffling .. we can give you a more specific answer on what to change!


Thanks John,

I'm sure , like me we read over all the notes to try and grasp what all this stuff means over and over. While not getting it at all. Then one day you read it again and you understand it a lot more haha.

BTW Nicoxis has stated what his issue is. The very slow, parking lot speed of light to no throttle and you get that embarrassing wild bucking horse phenomenon
2013-07-24 23:05:23
#22
Nicoxis, maybe were heading the wrong way. I just thought that since it doesn't do it in the cold we should try the colder values for the entire table BUT maybe try to lower the rpm down a bunch more, like from 40c to 100c
2013-07-25 01:40:29
#23
Originally Posted by Haulin200sx
I'm sure , like me we read over all the notes to try and grasp what all this stuff means over and over. While not getting it at all. Then one day you read it again and you understand it a lot more haha.

BTW Nicoxis has stated what his issue is. The very slow, parking lot speed of light to no throttle and you get that embarrassing wild bucking horse phenomenon



The easiest way around this is for him to take a log (TCL) and post it on here for us to view, also include your tune file (TCD) so we can suggest some changes.

One definite thing that will cause this issue is a TPS that is not functioning properly.

If it is right on the verge of hitting fuel cut and you keep your foot there, it will constantly surge back and forth between fuel and and fuel cut restore. This is something we can see in the log by watching the fuel cut flag.
2013-07-25 16:23:01
#24
You can watch the Throttle Closed flag and make sure it is consistent while opening and closing the throttle, and you can graph the TPS Voltage and make sure it is smooth and follows throttle movement consistently. Engine does not have to be running, only ignition ON.
2013-07-25 20:41:03
#25
i think RT was soo much easier to tune, wasnt too much of a jump going from nistune to RT, SA is a whole new beast, im still learning, its tough tho not really having gas to play around much, but im finally on SA an have a tune that doesnt run like poop lol.

good luck to to op hopefully yall figure it out.
2013-07-26 15:07:42
#26
Originally Posted by lynchfourtwenty
i think RT was soo much easier to tune, wasnt too much of a jump going from nistune to RT, SA is a whole new beast, im still learning, its tough tho not really having gas to play around much, but im finally on SA an have a tune that doesnt run like poop lol.

good luck to to op hopefully yall figure it out.


Just like anything, it takes some time and trial and error to learn something new.

Be patient with it and I assure you the end result will be something you will enjoy!
2013-07-29 06:34:27
#27
How does the fuel cut table control fuel cut on overrun? If i am doing say 3000rpm and back off, it seems to go into fuel cut as the afr goes to 22:1, but the fuel cut table are like 1900rpm or so.

Also do FC tables affect a situation where coasting up to a intersection with throttle fully closed, road is clear so press accel again, and power comes back on with a harsh kick.
2013-07-29 14:00:36
#28
When the throttle closes, if the RPM is above the RPM from the FUEL CUT ON RPM TABLE, fuel cut is activated. So in your example, if the RPM is above 1900 when the throttle closes, fuel cut is activated.

There are parameters in the SA version which let you tune more of the overrun fuel cut operation.

Dave
2013-07-30 09:53:10
#29
Oh. So Fuel cut on, at say 1900rpm, is actually when fuel cut turns off as the car decelerates on vacuum? Fuel cut transition is when 2 of the injectors come back on, and then fuel cut off, is when fuel cut turns back on as rpm drops.

I think the FC tables now make a bit more sense, but maybe the labels are a bit misleading. Reading the Help file does kinda reflect this, but i had never managed to interpret the words that way.

I think i might be able to make some use of this, cheers Dave.
2013-07-30 12:55:07
#30
Fuel cut ON = Fuel OFF
Fuel cut OFF = Fuel ON

Cheers,
Dave
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