Tune 'n' 'charge 'n' tune

[Loren]

Here's Publio's tune. I'm just guessing here. I *think* it was the one that I spent a bunch of time on and got dialed in pretty well. The only thing it didn't have was good cold start. (wasn't cold when I messed with it)

[Native]

So since 2/16, I've had a chance to mess with things once. But, it was good messing. I was able to improve on the improvements Loren made, and now it drives much more like a normal car. The acceleration enrichment was set to kick in too easily, and overall the enrichments were too rich, or to say the pulsewidths too large. No more major bogging, and driveability is much, much better. Datalogging showed me that for AE, the upper threshold is too low still (I can hit a TPSdot of like 1300), and in that situation that lean spike followed by super-rich compensation is back, with some mild hesitation. In English, that means during an autocross, if I've lifted, and then suddenly floored the throttle, rather than gas it gets air for a split second, then too much gas. What's good is I think I know how to fix it! Oh, and cold start is way better, but hot start isn't (I think I know where to adjust that, too).

[Loren]

Good stuff!

[Native]

Hi again.
I was able to play a bit last weekend, or was it the one before...?
Still chasing a bog on throttle input, and have an idea of what to fiddle with next time around after looking at logs and stuff.
Also messing with starts - especially hot - as it won't turn over without a good poke of throttle. I figured it wasn't enough cranking fuel, but with some reading had my thinking fixed with the notion that if adding throttle, that means adding air, which leans the mix which means too much fuel, as opposed to not enough. Also read that small adjustments can make a big difference. So, working the other way, it now only takes a slight touch of throttle for a hot start, and once, it actually caught by itself. Once. Heh. Getting there.

Cold start was "ok" but I messed with it, too. Of course, I have no idea where I stand until the next time I try to fire it up...

Also activated deceleration fuel cut. The cut is seamless, but it's a bit abrupt when it refires at the lower rpm set point, but I'll worry about that later.

[Native]

So the cold start changes were actually pretty good, and I made a few more tweaks...will have to wait to see.
Hot start is now functional - turns over without touching the throttle. But, it just barely runs, for a moment, so, there's more to play with, but solid progress there.

Have continued messing with the throttle response. It's trial and error at this point, and I have managed to get things better there, too. Slower throttle inputs are pretty smooth, but the quicker I get with the gas pedal, the more the hesitation. And I say hesitation as it isn't so much an outright bog anymore. I might maybe have a chance to fool with it tomorrow some. Or not. We'll see.

[Loren]

Way to go, Steve!

I see a lot of people dive into Megasquirt tuning with both feet and quickly get over their head, get discouraged, and give up on it. They either end up paying someone else to tune it, or they live with a wonky tune, or they yank it out and go a different route. I'm glad to see that you're sticking with it, gaining some understanding of how things work, and tackling your issues!

[Native]

Well, I am over my head, but I know it! So, I took, and take, the mindset that this is going to take some time, and a lot of learning. Indeed, I've spent more time at the computer at my desk than I have the computer in the car. And even with that, it's not coming quickly. But I haven't blown it up, either!

[Blue_Heron]

...But I haven't blown it up, either!

That doesn't happen until after you put the blower on, Steve.

[Native]

Hopefully that blower isn't far off:
I made some pretty big gains this last weekend. What I've read has said in so many Megasquirt words that small changes in settings can equal big changes in the way the engine runs. Well, I've been making changes to acceleration enrichment by tenths, to no good end. This time I said to myself, screw that, I'm making larger changes, so I started messing with solid round numbers. Way, way more enrichment. Like 2-3 times what I was using before. And it worked! The bog/hesitation is virtually gone. I tried to datalog it, but did something wrong there (of course... ), but I'll get that data next time, to just satisfy me that what the car feels like actually shows on the graphs.

Still chasing that solid hot start...

[CaptainSquirts]

Hmmmm, so you're saying you will be driving the miata this Sunday then?

[Native]

Heh. I probably could, but I'm not. But eventually I will. Just not yet.

[Native]

And a month later, I had the chance to play again, and I think I licked the hot start matter - made some changes to the IAC valve settings, and reduced the amount of fuel added during cranking and immediately after starting (it was flooding itself). Seems to turn over pretty reliably, and usually falls into a nice idle.

I've further refined the throttle response. I could sort of, kind of, feel some slight hesitation at higher rpm and rapid throttle opening, and the datalog, that I didn't mess up this time, confirmed what I was feeling. But, now I know what to tweak, and hope to have that adjusted sooner than in a month from now...

[Loren]

Isn't it awesome when you start wrapping your head around how the whole thing works, and can make it do what you want it to do?

[Native]

Well, I don't know that I'm quite there yet...

Been messing with it a lot this week - it's sooo close.
I've almost got the acceleration enrichment dialed in. Still working away a fast-throttle cough...
It starts well enough, but sometimes will take a pulsing/hunting idle, but usually on a warm restart - the first cold start is pretty good. Also sometimes after starting, it falls right into the programmed afr range. Other times it settles leaner, and may hunt. Other times it's even richer. In my head, it doesn't make sense based on cranking and afterstart settings, and sometimes it almost seems as if there's two settings fighting each other...I just need to get that straight.

[Native]

Handed the keys to Loren yesterday, and he offered a fresh review of the tune. Made some suggestions about sizes and durations of acceleration enrichments, and also reviewed some of the finer points of idle tuning. Also discussed redefining some of the fields in the fuel and afr tables to be more "friendly" to each other.

Gonna keep at it.

[Loren]

[Native]

Messed with this more today. But mostly inside on the internet.
Accel. enrich. is fine once the throttle is open, but initial tip-in coughs still. Tried all sorts of stuff - higher enrichment, short duration; vice-versa; everything in-between; cursing. It doesn't quite work. So, in thinking about a brief comment Loren made yesterday, about an AE setting for "TPS-based WOT%" that was "on", he said "good." But we never looked at it. I did today, and it took me several hours to get my head around it. I'm not sure I have, but here's the thing: the table has rpm on one axis, and TPS on the other. Currently, (well, currently it's "off") but the table is set to curve from like 20% tps at 1000 rpm to 100% tps at 7000 rpm. What that means is that, at low rpm, like at throttle tip-in, after the throttle position hits 20%, the computer thinks that's wide open, and it cancels enrichment. And at high rpm, it allows enrichment through most of the throttle (which I don't really need). Also, it's said to make the enrichment response more "sensitive" which is what I think it needs (because I understand "sensitive" to mean "immediate.") So, next chance I get, which will hopefully be some time on Sunday, I think I'll change the curve, such that at 1000 rpm, it's like 80% tps (at least to start)... If I've got this, that means it'll give more enrichment, and more quickly, and the cough goes away. (ohpleaseohpleaseohpleaseohplease).

If this doesn't work, I'm probably going to redefine the fields in my fuel and afr tables, and start from scratch. Gonna do that even if it does work, but I'm feeling stubborn.

[Native]

Ok, now we're getting somewhere. I set that TPS % WOT to 100% through the whole rpm range (which in hindsight is probably the same as turning it off) so it should not be messing with the enrichments. That helped. Then, as I was futzing around with datalogs, I noticed that MAP changes are much more sensitive to touch-of-the-throttle than TPS changes, and so I opened up MAP--based acceleration enrichments, and started combining that at a low introductory level, and that helped too. So much so that I added a bit more MAP combined TPS AE...I think it's 85% TPS and 15% MAP-based now, and that stumble is far improved. Still there though, but I think it's actually working but now I've added too much enrichment, which is what causes the stumble (and the occasional faint puff of black smoke in my rearview when I hit the gas just so...).

Isn't it awesome when you start wrapping your head around how the whole thing works, and can make it do what you want it to do?

Now it's starting to feel that way...

[CaptainSquirts]

So explain in less than 20 words for people that don't get the whole scu talk of what was done. Or a "I'm 70% done" kinda deal.

[Loren]

Hmmm... stages of Megsquirt tuning (more or less):
Initial setup (wiring, settings, installation) - check
First Start (set base timing and verify control of everything) - check
Basic Idle Tuning (get the idle stable) - check
First round "autotune" (initial fuel tuning by driving the car and adjusting to the WB02 feedback) - check
Start-up Tuning (easy cold and warm starts) - check
Acceleration Enrichments (getting rid of the stumbles, smooth transition to acceleration) - where Steve is now
Idle-up Tuning (smooth transition to faster idle for AC, etc) - check

And then you basically redo most of that again a few times, making it better each time.

And, as Steve is alluding to, once you've gone through EVERYTHING, and gotten things "kinda close", you've learned a LOT in that process. So, if you go back and start from scratch, you're likely to get it even better the second time, and it won't take nearly as long.

I'd say Steve is 90% there if he wanted to leave it alone. And it won't take him long to get to 95%. It's that last 5% that takes a long time. Partly because you have to actually drive the car in different conditions. Cold starts. Really cold starts. Warm starts. Hot starts. Really hot starts. And the entire warm-up process on any of those starts. Running with 80 degree ambient air, running with 110 degree ambient air. Strange conditions that you never really encountered in your street tuning, but apparently you do on every other autocross run. There are thousands of little bitty details to chase.