Stock ECU VE table
 

has anyone ever decoded the VE table in the stock miata ECU?

I wondered about this a long time ago. I think in the early days of MiataTurbo.net, somebody (for some stupid reason I think maybe Joe Perez?) built a Megasquirt just for datalogging purposes and logged the stock ECU spark and fueling.
I do remember reading about it in 07 or 08 I think. I know somebody did this...
Why exactly would you want to know the stock ECU VE table though?

when I drive my wife's bone stock miata and then drive mine; you can't find much to fault the excellent job the miata development engineers did

my thought was to duplicate the OEM VE table for the <100kPa part of my VE table to regain the benefit of that development; initial issues would be accommodating the change in exhaust back pressure, higher capacity fuel delivery, larger injectors, ... [so much for blindly duplicating the stock settings--lol]

I just think the stock settings would be a good starting reference

Something to keep in mind is that oem ecus often have multiple tables for both fuel and spark that they can switch between to optimize operation based on conditions (anyone know if the miata ecu is like this?). You may not have the hardware to replicate this functionality.

Aside from that it doesn't sound like a terrible place to start.

Not a VE table exactly, but this is the stock fuel table from a '94 BPF3 ECU as used by Tunerpro, from the "socketed ecu" thread on m.net:
https://www.miataturbo.net/attachmen...ine=1334195236

Stock ECU doesnt have a "VE" table, because its not speed density, its mass airflow.
Which means that the fuel table looks like what Sclippy posted, target AFRs which are referenced against the MAF curve to calculate how much fuel to deliver.

yes looks like an AFR table with rpm across the top
now how to decode the vertical scale
interesting break between step 10 and 11

good point on the mass flow basis
means looking at the ECU code for calculating fuel quantity

I am thinking the mass flow system is more dynamic [continuous] than the speed density system with the required fuel being calculated based on a number of sensor values; whereas the speed density system determines fuel need by interpolating between fixed reference values from the VE table

think I will snoop some on the m.net postings

a SD setup requires alot more inputs to do final fuel calucations then a MAF system.
You won't be able to really interpolate them because load on a maf system differs from that of a speed density setup.

The vertical scale is load based on engine output\tq
You can watch the load scale to see how efficient your engine is.
the maf itself is based on airflow\horse power

Unless of course you run megasquirt on a maf.
More then likely that table is more of a closed loop commanded afr table.
I wonder though what their power enrichment table looks like.
I also wonder how much spark timing they drop if any on shifting

I wonder how they could ever target anything other than 14.7 with a narrow band O2.

I doubt that table is a stock Mazda OEM table. Doesn't make sense given the sensors on the car.

why does it not make sense to you?

I think someone logged AFR with a wideband/pencil/paper device.

What I really want to see is the spark table.

https://www.miataturbo.net/attachmen...ine=1334245646
http://i39.tinypic.com/34zlhug.png

It doesn't, it just adjusts the long term trims based on O2 feedback whenever the motor is running in the 14.7 AFR region. The richer numbers in the table are used to calculate fueling in open loop.

The Y-axis doesn't appear to be simply the AFM output voltage.

It looks like this:

AFM voltage -> lookup table to output airflow -> divided by RPM to get VE (this is the Y axis)

Thanks Techsalvager. They left a lot on the table with table compared to my current 89-octane table.

y axis is a load percentage on maf based systems if it was N\a engine you would probably see around 85-95 at max load depending on engine setup. like I said before at WOT with a maf based system it doesn't go to 100 on an N\A engine like it would on a SD setup. it follows tq output, so you can easily see when your tq has peaked and then just watch maf to see when the hp peaks out.

hustler that because its not geared for a SD setup.
on the highway I cruise at 20-30 load. light accel between 30-60, idle is around 14-18.

Right. I looked at the MS screenshot.

Right, and to get that from MAF, you need to divide by RPM.

MAF gives you airflow in lbs/min. "Load" and torque are proportional to air consumption in lbs per revolution, aka amount of air ingested per cycles, aka V.E. To go from MAF to VE, you need to divide by RPM. The resulting table will be very similar to a VE table driven by RPM and MAP.

Is there any reason I should not take the entire bottom of that timing map and match mine? I'm talking about from the -6 to -20 PSI?

I have a datalog of how it looks like to use that map if you want to see.

at 5.5K where the timing drops, is due to the increase in fueling...so take that into account.


I'm sure Reverant already has all this data pulled from "stiming" the stock ECUs.

I scored about 3.5 mpg on a hurt motor at 78mph by tuning the cruise area.

How does this look. Before is on the right.
http://img33.imageshack.us/img33/7034/timingq.png

do you set your car to go pig rich after 5.5k?


am i on ignore?

Wasn't sure if you were talking to me. If you look- after 5.5k not much has changed on my map. But my fuel map does not reflect any crazy change after 5.5k.

that's the whole reasoning behind the massive retard at 5.5K.

there's a correlation. haromony between AFRs, timing and EGTs and whatnot.


If it were me, I'd just copy the entire 5000RPM column across to redline. only retarding in the area where you acutally do have your AFRs set to go richer.

It looks pretty weak to me but you have a VVT job on there and I won't assume what the numbers should and should not be. Just get it on a dyno and get it right.

Hmm.. I found that my map was more retarded in some of the lower load lower RPM areas.

In theory I should be safe if I match the factory ECU timing if not increase above what they have the timing set to right?

And as far as the 5.5k goes- I rarely hit that area of the map as is. On the freeway at 80 I'm sitting at 3400.

Because a narrow band O2 is darn near an ON-OFF switch that switches at 1 Lambda (~14.7:1 for gasoline). You could never control to an AFR of 10.2 with a narrow band.

OTOH, if the entries other than 14.7 really get used as open-loop mode multipliers, then I can see how it is workable. Seems convoluted though.

Looking at these tables, I see emissions and warranty rather than optimized performance in a lot of areas. Targeting 10:1 AFR at high RPM/high load looks like a kind of "soft" rev limiter (especially considering the "high load" we're talking about is slightly less than atmospheric).

You need to translate the Y axis to MAP.

yes oems have to target alot to make a fuel\spark map that can be used world wide and meet a lot of emissions requirement as well as their own warrnties.

Also running the engine rich helps at higher loads to keep the temp of cat under control and not overheat it.

then make yourself hit it by holding in a gear and reving into the area at cruise.

Tons and tons of cars gain a lot of torque, smoothness, and overall drive "better" with the megasquirt maps and proper tuning. There is nothing spectacular at all about the stock ecu fuel and spark maps.
I really don't see why everyone is so interested in this.
OP, If your lowend is not as good as stock it just means its not tuned worth a damn, and you need to get on that instead of trying to waste time converting the stock table for a "starting point". 80% of it, as mentioned already, is warrantte and emissions crap that hurts your performance if anything.

Only thing I'd be interested is seeing how the stock ecu controls idle, since I still haven't mastered a FLAWLESS idle with ms. But looks like some folks (like y8s, Reverant, and others) have shown videos of flawless idle on the ms3x so I'll probably pester them for their idle tuning secrets.

I'm just interested in the areas that are more advanced than what I was running. No point in that.

My idle is amazing with Adaptronic. I've honestly never been happier with an ECU.

That's because you let the stock ecu controll it, right?
Mine was controlled by the adap and sucked big time:(

Nope. Adaptronic is controlling it now and it's flawless.

What issues were you having?

Mine targets 14.5 and doesn't fluctuate more than 3-5% and my idle target table usually targets the set idle within 75-100 RPM.

My car detonated at ~100kpa, sub 3000rpm with the factory computer and detonated at 100kpa and 6000rpm. That's why I'm fascinated. I'm leaner with more spark angle now and not detonating.

I recently watched a presentation from an MS guy who's an engineer for Ford and he talked about how they'd spend so much time on tuning and cold-start that I don't understand why they'd do such a "weak tune" aside from the wonderful 85-octane mountain fuel.

I fit's any consolation, Jeffman's car had some crazy whacked out crack ----- settings for spark at idle and idle valve settings on that supercharged car. They were pretty easy to get right on his supercharged car. For some reason the enrichment settings were a real bitch on my daily.

You really don't need crazy anything. I'm running 10 degrees ignition at idle with my idle valve in closed loop control. Once you get your PID settings correct (there is an excellent guide to this) you are all good. Just make sure your fuel is set properly.

I don't really remember what exactly the issue was with the Adap, all I know is when I switched to MS, id1000's and e85, 99% of the issues were gone and I was enjoying my car again lol.

Yeah. The only downfall I can see to the Adaptronic is that it allows you to change just about anything you could imagine. So unless you know what you are doing you can really put things out of whack.

But this in my opinion is way better than being frustrated with too few settings. My car legitimately starts runs and idles like its bone stock. Warm up and all.

The problems I had on his car with Adaptronic defied logic.

Because nobody has tried to tune the part throttle timing maps by looking for MBT?

THe Adap had a great feature, its "MBT finder", which nobody used... so it was taken out.

I messed with it using your suggested technique of staying under 100kpa and all that, but you're right: I don't think any of us REALLY used it.

What makes you think the OEM mapping is tuned to MBT?

It'll have to be pretty close, in order to improve MPG.

Am I the only person who is entirely uninterested in what the stock ECU does? I tuned a fairly stock '94 last week and found nearly 20ft.lbs of torque at 3000rpm by switching from the stock ECU to an AEM EMS.

If the stock ECU is that far off the mark, then I prefer to just ignore it entirely and build my own maps.

that's what I've been saying in basically every post

And Sav is saying the factory WOT maps aren't good.

Has anyone shown that the factory part-throttle maps are similarly lame?

Has anyone attempted to tune part throttle on the dyno?

I mean, what's the point of having a load holding dyno? If you are just doing WOT RPM sweeps then a Dynojet will be almost as good.

I will be doing driveability tuning on the local dynojet once I deem my car ready.
part throttle and traistition tuning.
and a dynojet can do it if it has a load cell

Are you going to attempt finding MBT at part-throttle?

ah forgot to post, but yeah that is the goal.

Only on my turbo car. I've added a ton of spark to my daily everywhere and not confirmed MBT on a dyno, but it's significantly faster and easier to drive. I can't imagine not tuning part throttle. I did this to maximize fuel economy...then promptly destroy that fuel economy with enrichment tuning.

Well mine is also running pretty advanced compared to stock, about 6 degrees advance on the whole map taking into account the fact that the car is pre-tuned for 91 RON, and we can only get 95 RON over here. But even though the drive is awesome, I'm worried that there could be detonation... Anyway to figure it out without buying some det cans?

Bump to say: yes, that's one of the things i found in the '94 BPF3 ECU code. The lookup table is between addresses EE1C and EF02 in the ROM and it occurred to me you could run a different model of AFM on the stock ECU just by editing that table.

A solution looking for a problem, I guess. It would be some use on a 1.6 where you could fit an RX7 AFM instead, but not much use on a 1.8.

Anyway,the law of the lookup table looks like this:

https://www.miataturbo.net/attachmen...ine=1337345639
(X-axis is input value, Y-axis is output)

hmm need to compare with obd 2 data output on a newer car
X is voltage\adc
Y is airflow
Don't know off hand what airflow units those are because 640g\s is way to much for this maf and 64g\s is way too little

It's only the shape of the chart that's meaningful; the actual numbers are arbitrary. It's not reading airflow in any particular units. It just takes a voltage reading from a 10 bit A-D input and uses that to interpolate a value from a 7 bit lookup table to produce a 16 bit output.

Whatever it does next with that value (divide it by rpm?) will rescale it again.

ok, appericate the feedback.

I reckon the AFR target table on the first page makes no sense at all. While on open loop the ECU won't cycle the fuel mixture according to the narrowband sensor, thus that table makes no sense for open loop. And on closed loop it always fluctuates between 14.5 and 15.3 (that, I tested myself) independent of load or speed. Of course, if you go near WOT, or into high revs, the ECU steps back to open loop, therefore that map does not have any meaning in practice. I reckon, if that map was stimmed, then it serves only as a very rough readout of AFRs on a mix of open loop and closed loop...

it very well has meaning. it is the commanded AFR map the ecu uses for fuel calucations

How so? It can either go one of two ways...

Either that map was read out of the original memory, and it only makes sense at a purely theoretical level (such as, the ECU calculating the fuel to match this AFR from the AFM data and the injector capacity), and it will not correspond with the actual value because there are always slight variations

or

this map was read from the ECU by stimming it and/or driving around and logging results, in which case it's a mix of open and closed loop driving. I know someone said some posts before this one, that the ECU can't read anything other than rich or lean from a narrowband (which is true) but it can use these values to modify the turnpoint of the lean/rich wave signal, which would work in theory, but like I said there is no change to the AFR targets in closed loop mode in practice.

So, I have no idea what to make of that. Would be nice to be able to set up a Megasquirt to run just the same as the factory ECU, and tune from there, though!