Fuel maps

[lamcote]

I asked Scannerdanner (YouTube ECU guru) a question about fuel maps and he has replied.

I asked if the ECU used learned closed loop fueling to modify open loop maps.

He says no, because the car isn't interested in achieving stoichiometry in open loop, it never modifies open loop maps.

Interesting.

[jonbill]

I reckon there might be a few assumptions, guesses and lack of imagination in that answer.
Clearly fuel trims calculated during closed loop targeting stoichiometry could be used used to adjust fuelling in open loop targeting other lambdas.
Unless scannerdanner writes all the ecu software out there, he/she can't know it isn't used.

[lamcote]

I don't think you can have target lambdas in open loop because there is no mechanism to measure lambda in open loop as the O2 sensors are ignored because they're narrow band sensors which are only useful for indicating stoichiometry, ie they don't report actual lambda.

[jonbill]

The open loop map is targeting something, whether it has a feedback loop confirming it reaches its goal or not.
So for the sake of argument, let's say the open loop map is targeting max power with an acceptably long life. That will have a strong correlation with a certain lambda, perhaps 0.9.

Now consider, as the ecu software designer, that you can see that the closed loop fuel trims might tell you the ecu is adding 10% more fuel above the original map in closed loop conditions.
Its pretty likely that whatever caused the lean condition in closed loop is also there in open loop.
Why not add 10% fuel to the open loop map every where? Its likely to be a good move.
Its very unlikely to be a bad move.
How can scannerdanner know that toyota ecu designers didn't do this? Or anyone else for that matter?

[lamcote]

He is pretty competent, have you seen his videos?

[jonbill]

He is pretty competent, have you seen his videos?

No of course not, I don't let things like that stand in the way of holding a contrary opinion [emoji28]

[shnazzle]

All I would say is; reset ecu. Go for a drive and monitor open loop right at the beginning.
it will be 0. Because open loop does not feed off o2 readings.

... Then keep driving... And you'll find your fuel trims changed for open loop.

[lamcote]

Just having a look round at open loop fuel trims, there is some evidence that US and EU ECUs treat them differently on some cars!!

Can't we get some hard feedback from someone, one NSX site has the entire fuel logic mapped out in a diagram showing all the inputs and decisions being taken by the ECU. That would be so helpful.

[shnazzle]

This is turning into another "post-cat o2 doesn't affect fueling"

[lamcote]

The question is, what is it that affects the open loop trims. If I'm honest I find it hard to believe Toyota just extrapolate from the closed loop trims. When you consider that in closed loop there seem to be multiple cells for the fuel trims for the same load/revs meaning trims in closed loop are massively complex, are they really then just going to guess what might be right in open loop. It just seems so unlikely?

[jonbill]

The question is, what is it that affects the open loop trims. If I'm honest I find it hard to believe Toyota just extrapolate from the closed loop trims. When you consider that in closed loop there seem to be multiple cells for the fuel trims for the same load/revs meaning trims in closed loop are massively complex, are they really then just going to guess what might be right in open loop. It just seems so unlikely?

I think extrapolate is a good word for what they can and may be doing. Call that guessing If you want.

It's also possible they're using the o2 sensors in open loop.

[lamcote]

I don't think narrow band O2 sensors are accurate or fast enough to work in open loop.

It's so frustrating to think that there might be a whole strategy working away that we just don't know about!

[shnazzle]

I don't think narrow band O2 sensors are accurate or fast enough to work in open loop.

It's so frustrating to think that there might be a whole strategy working away that we just don't know about!

Correct. Narrowband is too slow for open loop.

There's definitely a strategy working away, which is frustrating, but also gives a lot of confidence.

The fact that @spit runs a turbo kit on the stock ECU speaks volumes of how many strategies there are and how good they are.

[lamcote]

Oooh, I didn't know about the spit turbo thing. Is there a thread with all the details anywhere?

[shnazzle]

Oooh, I didn't know about the spit turbo thing. Is there a thread with all the details anywhere?

Ha there probably is somewhere in the dispersed annals of early 2000s ROC. I'll have a dig but I think it's as simple as tinkering with the fuel pressure.

[lamcote]

Cheers. Presumably it was boosting about 4-5psi ish?

[jonbill]

I don't think narrow band O2 sensors are accurate or fast enough to work in open loop.

It's so frustrating to think that there might be a whole strategy working away that we just don't know about!

Correct. Narrowband is too slow for open loop.

There's definitely a strategy working away, which is frustrating, but also gives a lot of confidence.

The fact that @spit runs a turbo kit on the stock ECU speaks volumes of how many strategies there are and how good they are.

Too slow for an instantaneous corrective feedback loop, yes. Too slow for any kind of adaptive algorithm though? I doubt it.

[shnazzle]

I don't think narrow band O2 sensors are accurate or fast enough to work in open loop.

It's so frustrating to think that there might be a whole strategy working away that we just don't know about!

Correct. Narrowband is too slow for open loop.

There's definitely a strategy working away, which is frustrating, but also gives a lot of confidence.

The fact that @spit runs a turbo kit on the stock ECU speaks volumes of how many strategies there are and how good they are.

Too slow for an instantaneous corrective feedback loop, yes. Too slow for any kind of adaptive algorithm though? I doubt it.

Easier to extrapolate the adaptive from the closed loop areas when the narrow band can keep up with the various load changes instead of potentially being behins the curve all the time in open loop. Even for the occasional reading.
Also, more hydrocarbons in the exhaust at higher loads (open loop) which greatly reduce the reliability of narrowband readings.

[jonbill]

Yes, extrapolation still seems a good strategy to me, but the alternate strategy I'm thinking  of that uses the o2 sensor in open loop is this:
Forget correcting the 'now' fuelling.
Requires o2 sensor latency to be consistent and known. Let's say 200ms for the sake of argument, but it doesn't matter.
Then, when we get an o2 sensor reading, we can adjust the fuelling for the map location of 200ms ago. It doesn't help us now, but it will help us next time we visit that map location.

Dunno about the affect of slightly richer mixture on whether the o2 sensor can accurately read. I would expect it can accurately read for any AFR value intended by the ecu designer. I can't find anything on the Internet about it - have you got a link?

[shnazzle]

Yes, extrapolation still seems a good strategy to me, but the alternate strategy I'm thinking  of that uses the o2 sensor in open loop is this:
Forget correcting the 'now' fuelling.
Requires o2 sensor latency to be consistent and known. Let's say 200ms for the sake of argument, but it doesn't matter.
Then, when we get an o2 sensor reading, we can adjust the fuelling for the map location of 200ms ago. It doesn't help us now, but it will help us next time we visit that map location.

Dunno about the affect of slightly richer mixture on whether the o2 sensor can accurately read. I would expect it can accurately read for any AFR value intended by the ecu designer. I can't find anything on the Internet about it - have you got a link?

Doesn't quite work that way. For that to work, the car would need to maintain a running buffer of a lot of system parameters alongside a timeline to then be able to place the o2 reading at the right load levels, which can change a hell of a lot over a second. So the buffering would need to be at millisecond accuracy at the very least. Then you need to know the exact latency of the reading in relation to the firing event. If that were possible, we'd have open loop tuning
Instead they came up with a much more reliable solution... a wideband sensor. And even that has a latency. But take Helen's car for example, it adjusts fueling automatically to a set target based on wideband feedback. Constantly.

[lamcote]

I've always assumed that the reason there is an open loop strategy is precisely because that's the area where the O2 sensors are no good.

If the O2 sensors could manage, that would be included as part of the closed loop strategy.

[shnazzle]

I've always assumed that the reason there is an open loop strategy is precisely because that's the area where the O2 sensors are no good.

If the O2 sensors could manage, that would be included as part of the closed loop strategy.

Well we are talking mr2 specifically here.

With wideband you don't need a complex strategy. You just need a PID adjustment strategy and a target.
So no long term or short term because its all on the fly. Only short term.

[lamcote]

I've always assumed that the reason there is an open loop strategy is precisely because that's the area where the O2 sensors are no good.

If the O2 sensors could manage, that would be included as part of the closed loop strategy.

Well we are talking mr2 specifically here.

Agreed.

I'm still not happy with the extrapolation theory though!

[shnazzle]

I've always assumed that the reason there is an open loop strategy is precisely because that's the area where the O2 sensors are no good.

If the O2 sensors could manage, that would be included as part of the closed loop strategy.

Well we are talking mr2 specifically here.

Agreed.

I'm still not happy with the extrapolation theory though!

Take up your complaint with the fine chaps at Toyota

What I will say though is that, oddly, the long term fuel trims in open loop seem to want to be at 4.7. It'd be interesting to see what others have