Funny fluctuations

[Will guthrie]

Hi There,

I've been trying to fine tune my tune on my 1995 WRX STI, Generally it drives great, cruises well and holds reasonably close to target lambda during wide open throttle. But I can't seem to get the more transient zones right. when I button off the Lambda dips rich (suspect charge temp?) and sometimes when I just ease on throttle it can spike lean and over correct. I don't notice it in the drive of the car, but I'd love to know how to get it right.

I have road tuned it myself with basic knowledge. (links "What's this" function serving me well) 

log 12-8-23.llg 12th August 2023 tweaked charge temp table.pclr

[dx4picco]

If you don't feel jerking while it's has the transient lean/rich then I guess you shouldn't worry too much

[Adamw]

Your fuel control looks pretty acceptable to me.  The richness when you lift off is the fuel film or "puddle" evaporating off the port walls due to the higher vacuum in the port, it is normal and not much you can do about it.  

Your accel enrichment looks good for the most part, the only two places in the log where you get a small lean spike when you gently open the throttle is because there was an overrun fuel cut active at the time, so you have dry port walls etc.  If you cant feel this as a hesitation then I wouldnt bother trying to improve it.  If you can feel it then you could try increasing the accel load correction a little more in the 0%TP cell. 

For your interest, Shane T does a nice layman's explanation video of fuel film effect here:  https://youtu.be/LTXPF-6M1D0

 

 

[Will guthrie]

Hey guys

That's great, thanks heaps for taking a look! That guys video was brilliant. I thought I kinda understood the concept but he made it way easier to understand.

I've tweaked up the Accel load correction at 0% TP, I'll load that up and see if that helps.