Throttle Follower and Cracker

[goatkart]

Hey gang, was messing with the idle on my H/C car while i had some spair time... none the less... i was trying to pay particular attention to the follower and cracker, trying to see what they are doing in relation to my idle and surges etc.


what i was looking for are some guidelines... what should be doing what and when should it be doing it...

there are plenty of tables describing these tables but i couldnt find anything that concretly said.... adjust decay when X scenerio's occur, adjust total value why X scenerio occurs, adjust follower when this happens, adjust cracker when this type of thing happens...



my problem tends to be a decel surge(more rarely a stall), generally after an agressive throttle transition... say i do a quick rolling burp to spin the tires at a low MPH, often if i let off the gas completly, what will happen is either a surge, or a stall all together... do i need to make my follower/cracker tables more aggressive? decay slower?

my ltit and stit are zero +/- .2-.3 g/sec....

let me know your thoughts... and perhaps some things to look for...

[SSpdDmon]

http://forum.efilive.com/showthread.php?t=4661

I know it's "the dark side" for some of you folks...but, see if you can find these tables in HPT.



You issue may be timing related too. If your timing is bouncing around during decel, it may be perpetuating the problem.

[goatkart]

lol dark side!


its not a timing issue(fairly confident), timing is great, and when idle kicks in does its job perfectly...

decel is fine, no bucking etc, nothing really happens to cause my problems until the RPM's are getting low with mph higher(automatic with a stall)

i had a vision in my dream last night of how follower and cracker should work....

my thoughts were...

cracker is like RAF except at mph and rpm.... in other words, adjusting for idle condition at speed.... so while your slowing down with 0% tps, the effective idle air would be higher because rpm and mph would be higher.... kinda like if you idled at a higher rpm...

follower is all about rpm set down... more or less, how when your breaking the IAC closes up to idle..... and how softly it sets it there....

follower air being effectivly the idea of running to much idle air on purpouse... you run too much, and idle hangs, but if you can run to much, and decay the value to idle, you can slowly settle the rpm down to idle...

follower decay being how it flutters down...to slowly, and idle floats as your deceling.... decay to fast, and it dives to idle and probably over shoots....

follower delay being more about shifting etc.... more or less, we dont always want the air and rpm to drop.... if we dont,shifting will occur smooth kinda like rev matching.... so put a delay in the decay, and voila, rpms will hang before coming down...



this is how i am seeing this in my head at the momment.... this is also why so many like to run zero cracker at near idle conditions.... as cracker air will try and hold up the rpm.... and if you get fluxing rpm and steady mph or worse yet, fluxing BOTH... your cracker air will be going all over the place...


again, this is all in my head at the momment, which is why i am trying to figure out whats really going on...

[eficalibrator]

As a point of interest here: Keep in mind that RAF and throttle cracker airflows are based on whatever airmass estimation you have coming from either filtered MAF or dyn_air (speed density VE or equations). ANY error in either of these models will make RAF and throttle cracker calibration that much more frustrating.

Taken a step further: Since most people aren't developing their air models based on actual flow bench data, but rather based on wideband feedback, the errors mentioned above will also now include wideband error and mismatches in the fuel injector values. This includes IFR, short pulse adder and offset.

Yes, you read that right. If you tuned your MAF and VE based on wideband feedback but didn't use the absolute correct short pulse adder or injector offset, it can make tuning the RAF and throttle cracker difficult. This is why it's so important to start with ALL of the right values for the actual injectors being used.

This may or may not be the case here, but it's one of the first questions I'd ask before getting too deep into trying to correct something that may not actually be wrong! Always make sure the fundamentals are 100% correct first.

[SSpdDmon]

...but didn't use the absolute correct short pulse adder or injector offset...

Where do we find said data? Without a lab full of thousands of dollars worth of test equipment that is...

[goatkart]

As a point of interest here: Keep in mind that RAF and throttle cracker airflows are based on whatever airmass estimation you have coming from either filtered MAF or dyn_air (speed density VE or equations). ANY error in either of these models will make RAF and throttle cracker calibration that much more frustrating.

Taken a step further: Since most people aren't developing their air models based on actual flow bench data, but rather based on wideband feedback, the errors mentioned above will also now include wideband error and mismatches in the fuel injector values. This includes IFR, short pulse adder and offset.

Yes, you read that right. If you tuned your MAF and VE based on wideband feedback but didn't use the absolute correct short pulse adder or injector offset, it can make tuning the RAF and throttle cracker difficult. This is why it's so important to start with ALL of the right values for the actual injectors being used.

This may or may not be the case here, but it's one of the first questions I'd ask before getting too deep into trying to correct something that may not actually be wrong! Always make sure the fundamentals are 100% correct first.

your absolutely right unfortunately greg.....i wish i could argue the point, but theres nothing to argue.... its a compound of error situation.....

the best i can really say is i am certain i am "close" on all of those points, but thats all i will ever be able to say as a hobbiest tuner....

unless Bob over at PM-FL comes up with the maf tuning flow bench setup... which would be pretty sweet....

and you release injector values for us to use including offsets

that said....

i spent yesterday night logging follower and cracker data, and trying to tie it up to some significant insight.... which i cant say i got to much from honestly...


honestly, i got more insight from coasting down a hill off the throttle than i did from any driving and logging...

from a standing stop, i coasted down a hill, and when suddenly rpm jumped up and i looked to see the cracker jumped up too... and i realized i was seeing a similar condition to "too much RAF" where i was floating the idle while coasting down a hill...



so obviously, i was seeing to much "cracker air" for that situation...

and since its based relative to mph and rpm, it wouldnt decay until i came to a stop...



what i havent been able to do yet, is tie idle coast down surging to IAC air...

my mind is just not wrapping around that connection....

the best connection i can find is, like i mentioned up above..

cracker air is all about steady state idle style airflow except at a mph and rpm.....kinda like the RAF adder for movement.....

follower air is all about decel rpm....and setting the engine down "softly" so to speak....

and delay decay and airflow values are the three axis of how it gets there...



what im not TOTALLY clear on is, do both follower and cracker air need to be zero for idle control to take over.....


in other words, i have lots of questions running around about these two airflow controls...

[Bad WS6]

my problem tends to be a decel surge(more rarely a stall), generally after an agressive throttle transition... say i do a quick rolling burp to spin the tires at a low MPH, often if i let off the gas completly, what will happen is either a surge, or a stall all together... do i need to make my follower/cracker tables more aggressive? decay slower?

This is the EXACT problem I'm having with mine. Is it a follower/cracker issue, timing, too much fuel? If I get a copy of my tune and a scan can someone look it over for me?

And more detail on the car:

TSP 228R (228, .588, 114lsa), Patriot LS6 heads, LS6 intake, stock ported TB with hole drilled, tuned locally.

Everything about the tune is perfect except for coming off of throttle, it starts to surge wildly and sometimes wants to stall. When it's cold, it'll stall coming off of anything over 25% throttle. Quick throttle blips will get it pretty much every time.

[Bad WS6]

This is my current tune. Again, any help is appreciated.

[Eagle]

Your idle spark advance (in drive and PN) has quite a nasty swing (28 @ 0-400, 22 @ 800-1200, 30 @ 1600)... if you're swinging between these RPM ranges that timing bump is probably enough to get it surging.

Your ETC and IAT spark tables are both zero'd too... any reason why?

Throttle follower delay seems excessive too. I've seen much larger cams run on less.

Search for Russ K's idle.cfg and post a scan with some data... if you don't figure it out yourself after seeing the data!

[Bad WS6]

I'll pass that on to my tuner and see if I can get a scan with that config. Thanks!

[Eagle]

You bet, good luck!

[Bad WS6]

Did a scan in gear with the Russ K config last night. We updated the base running airflow with the results as well as making some other minor tweaks. The one that made the biggest change was lowering the adaptive idle minimum ECT to 150. The off-throttle surging is now gone above 150 and noticeably better over 110 or so. The cold start surging with any kind of throttle input is still unchanged from before the changes. Here's a copy of the scan and the current tune. Any input is appreciated.

[blownbluez06]

As a point of interest here: Keep in mind that RAF and throttle cracker airflows are based on whatever airmass estimation you have coming from either filtered MAF or dyn_air (speed density VE or equations). ANY error in either of these models will make RAF and throttle cracker calibration that much more frustrating.

Taken a step further: Since most people aren't developing their air models based on actual flow bench data, but rather based on wideband feedback, the errors mentioned above will also now include wideband error and mismatches in the fuel injector values. This includes IFR, short pulse adder and offset.

Yes, you read that right. If you tuned your MAF and VE based on wideband feedback but didn't use the absolute correct short pulse adder or injector offset, it can make tuning the RAF and throttle cracker difficult. This is why it's so important to start with ALL of the right values for the actual injectors being used.

This may or may not be the case here, but it's one of the first questions I'd ask before getting too deep into trying to correct something that may not actually be wrong! Always make sure the fundamentals are 100% correct first.

I ordered your books. Can't wait to get them. Hoping you're going to give up the goods on "the right values" .

[Bad WS6]

Took the car out for a bit this afternoon and the surging came back. I let it sit for about 20 minutes and came back to it with the ECT still at over 170*. It started surging like crazy while I made some parking lot maneuvers, then cleared up once I hit the road again. A little later, I was sitting at stoplight for 2 minutes or so and it started surging as soon as I took off again and then let off the throttle. Any ideas?

[Bad WS6]

Now when restarting the car hot, it just dies right away. Can anybody help me with this?

[Bad WS6]

Thanks for all the help.