NefMoto

Anyone else run into this with large MAFs?  Every other part of drivability is good, rock solid idle, but when having been in upper revs for a bit then pushing in clutch to come to a stop it will idle down too far and die.

This has happened off and on to me, mulitple cars, all mbox and all atleast an 85mm maf.  I would play with idle tq but I am wondering why its hit and miss even on the same car.  When it starts to do it you have to coast down in gear until you are under 1k rpm and then just pop the lever into neutral to stay running.

never had this issue... how are the A/F's?

are the injectors not coming back on in time?  when do they come back on for you coming out of over-run?

are you running a lwfw?  my guess is no on the unicorn, but from an engineering point of view you would want to take the two idle torque reserve maps:  with clutch-in and without.  To these maps you'd want to find a decimal K such that

new_map_with      = (1+K) * old_map_with
new_map_without  = (1+K) * old_map_without

For brevity assume that K is the same for both idle torque maps.
Calculation of K should be as follows:

K = inertia old / inertia new = (mOld*R^2) / (mNew*R^2)          are you running the same clutch diameter?  i never know with the unicorn, chicks dig it ya know.

assumption:  yes.     therefore:  K = mOld / mNew  --->

(28 lbs / your LWFW in lbs)  = (K+1), find K.

that's what i'd do anyways.

I am going to guess that your TVUB for injectors is all off (too little). I've had this behavior on dekas 660 and bosch 1000cc, TVUB was too small on both occassions. At a very low MAF reading, the TVUB value is majority of injector on time. If TVUB is only a little off, you will either get a lot less or a lot more fuel than you really need. In the case of TVUB being too small, the engine will just die as there is no time for ECU to intervene to bring AFRs up.

I had this when running 550cc injectors, just cut out at low rpm after a good thrash, raised TVUB and problem cured.  I have a TFSI in with the same issuse which I am working on tonight, fingers crossed it will be a simlar issue

I will have to explore the TVUB thing, ironically I have been planning to redo it on my car.  I think it does have to do with lighter mass flywheel/clutch setups as every car i have ran into this on was running something lighter than stock.  I run a CM850 twin and it is a lot lighter than stock.

I have left tvub alone all this time, my injectors dont even have published specs and so i am just going to have to jump in and tune it.

what injectors are you running?  also did you disable your LTFT's?  i've found them to be tremendously help for centering TVUB...

modified GM injectors (Lucas) at 90lb

I do not use LTFTs but I can, I just don't have the n80 hooked up.  On my personal car i don't care too much about getting tvub perfect but will make an effort.

the maf thing is just weird to me and I know it happens on other peoples tunes, even big name OTS stuff.   I will try to log it happening.

why not just calculate the constant i suggested?  i mean maybe it doesn't work but it seems simple enough.  what's your vacuum reading @ idle?  the other option is to look at your actual load versus rpm with the third axis being avg (wideband afr) and do the fueling correction on kflf.  a different method, but i suspect either would fix the problem you described.

 I feel like you could fix this a few different ways depending on what the real issue is, but the maps I might look into would be ,PVLDNV , PVLDN ,
 KFRLMN,KFMRES,KFMRESK,KFMDS. 

What is your pre-maf induction setup like?

Funny anecdote:  If you drive a Ford GT with the rear cover off, a light breeze can blow through the airbox and stall the car when you're declutched and coming to a stop.

4" dry flow down in the bumper, smooth bends to maf.  i would think its isolated but who knows.

(http://www.vlmspec.com/assets/images/s4/single/sm-4937.jpg)


(http://www.vlmspec.com/assets/images/s4/single/sm-4979.jpg)

I am having the same issue.  Is it possible that an inaccurate TEMIN value could cause this?

maybe, i lowered mine recently from .35 to .33 but havent driven it enough to see if it is changing better or worse.  Maybe its flooding it out coming into idle you think?  I can test a drastically low number and see if there is a change with this specific behavior.

another though, maybe its starved and needs more fuel and the lowered temin is doing it, every modded file for my cara nd other ko4 and up cars i have played with has gotten bumped down from .50

i seem to recall on mostly stock files i made for myself to test maf settings and a temin being left stock it didnt do this.

I just adjusted TEMIN from a stock value (AWP 1.8T) of .75 to .61.  I took it out for a few hard runs and didn't notice any difficulty holding idle after dropping from high revs.  This could just be a coincidence as the problem was pretty intermittent for me.  So I'll monitor and follow-up.

Finally cured this and I am Bummed I never took the time t dig into it.  It appears to relate to modified throttle maps, specifically max desired plate angle, I had made mine capable of 100% just out of idle, about 950 rpm, this is not the way to do it.

Basically it allows the ecu to over shoot its attempts to idle smooth, when the car has been ran hard and then you let off it has to come to a close and then bounce back open for a second to maintain idle, with the map edited too aggressively it will re-open way too far.  This then spikes the maf readings to way high for idle, adds to much fuel and snaps the throttle back shut abruptly and stalls the engine.

I simply made the map stock to 2500 rpm and then allow 100 after that, no more idle bouncing, no more issues.