brillo

This is a great discussion that should be sticky. I can't remember, is WOT really 70% throttle or greater? I know its not just 100% pedal to the floor.

Given what we know about closed and open loop, how does the emanage control a turbo setup the under partial conditions?

zoom44

ahh that last question of yours is excellent considering the timing of jeff just having put his now TCd car back on the road

how is the emanage handling things MazdaManiac?

shelleys_man_06

From what I learned, closed loop control means your outputs are dependent on your inputs, whereas open loop is independent of input. Is that what you're getting at Hymee?

dannobre

iTrader: (3)

open loop still uses inputs and gives outputs......it just doesn't use o2 derived A/F adjustments........ie feedback loop

bureau13

Actually, I think you mean your input is dependent on your output (in closed loop) not the other way 'round.

jds

shelleys_man_06

What do you want from me, I failed my design class.

RX8FOREAL

I have an interesting set-up thanks to Acosta Motorsports. They have installed a Super AFCII air fuel controller. This is similar to the VTECH controller for those former Honda people as myself to adjust the AFR for multiple RPM points. To tune properly, they just installed an AEM Wide Band O2 air fuel gauge. This gauge is very accurate, in fact real time AFR readings, which is what is suggested for AFR tuning. I have been playing around with unit and "feel" some improvements. I have not had a chance to dyno, but I have made adjustments to low throttle as well a high throttle to add some fuel where the AFR was too lean. The air fuel gauge is mounted on the dash next to the A pillar. I am having fun monitoring since the gauge is digital but also has multi LED's, green (rich), yellow (stoich.) and red (lean). I am on a never ending quest to keep improving a good thing !

Hymee

iTrader: (1)

I'm really shocked at what I typed in my last post on this thread (it was a long while ago!!!). I'm not afraid to admit it though.

I remember typing that post after a long conversation with CZ about how Closed Loop can be tuned. I'm a bit shocked and embarrased that I let him convince me of some of that.

Closed Loop
By definition, Closed Loop mode means the computer is constantly monitoring the Air:Fuel Ratio (AFR), via the 02 sensor, and making fuel delivery adjustments to maintain the "ideal" air/fuel mixture (Stoichiometric) for complete combustion. This is an important function for reasons of efficiency and the environment. It is a feedback loop - if something happens to make the AFR richer or leaner, the computer puts in less or more fuel respectively. The only way to trick the computer would be to fudge the O2 sensor - but there is no point to that at all. It is a highly accurate device, and what it is detecting is very valuable info.

The engine is running in "Closed Loop" mode most of the time, except in "heavy" acceleration and also decellerating on a closed throttle. More on this later.

Open Loop
This is when the driver is commanding "power". The best AFR for power is richer than "stoich". And things are changing so rapidly (i.e. RPM rising, Air flow rising, Throttle position changing rapidly etc), that the computer does not really have time to react in a "feedback loop" manner. Hence the loop is no longer closed, but rather "open". In this state, the computer is looking at all of it's inputs (RPM, MAF, TPS, Temps, BARO etc...) and working out how much fuel to dump in for each injector squirt by looking at a fuel delivery schedule table locked away in the PCM somewhere. It doesn't take note of the AFR and make any adjustments - as there is no feedback.

Just where does the computer go from Closed Loop to Open Loop? Simply put, light throttle will be Closed Loop, and heavy throttle will Open Loop. A scan tool (such as the sCANalyser) can tell you directly if the engine is running in Closed Loop or Open Loop, as there is a mandatory ODBII parameter for it. But you can also tell by looking at the AFR. In the RX8 we already have a wide-band 02 sensor, and if we monitor that, or even any other o2 sensor shoved up the tail pipe or stuck in the eahaust manifold, we can easily see when it drops out of closed loop into open loop, and vice versa. How? Well when it is in closed loop, you see a nice AFR of 14.7:1 (or Lambda = 1.0) or very close to that. As soon as the AFR reading deviates much from that, you know you are in open loop. Simple!

I hope this clarifies my position. I am a firm believer in not tuning the car in closed loop. It is totally pointless, and without merit. By definition, the car is tuning itself in this condition, and all of my experience with logging RX-8 real-time data shows it does a very good job of it.

Cheers,
Hymee.

NOTE - I have not logged an "exact" Throttle Position where the transition from Open to Closed loop operation happens. Nor do I believe it will always be at a certain throttle opening. It probably depends on a number of inputs, such as TPS, MAF and RPM. It is probably more of a % Calculated Load type of thing, rather than a single physical sensor input.

smrx8

iTrader: (1)

When i talk to marcus at acosta he says you should see about 9 hp the most.i was going to have him install it and dynoing it but told me right off the bat.you will not get much.so i decided to stay away.

Hymee

iTrader: (1)

9 HP is the same ballpark to what we have seen on the AU cars and a piggy-back. So a few of us agree that the best use for a piggy-back would be in FI.

Cheers,
Hymee.

Zaku-8

Sorry to resurrect this thread but I was going through it and am still unclear as to the sub-thread between Hymee and MazdaManiac on the PCM still reading to the WBO2 sensor in open loop. Doesn't this mean that the PCM always operates in closed loop? If not, then for what purpose is PCM still reading the sensor?

Hymee

iTrader: (1)

The PCM operates in both closed loop and open loop. This can be verfied with an ODBII scan tool such as the sCANalyser. Even watching the O2 sensor readings you can see when it is drops out of closed loop into open loop, as the AFR alters dramatically from stoich.

Cheers,
Hymee.

Barf

This cache-lookup behaviour seems to explain something my wife first noticed on our '8. Shifting upgear on a certain rpm, you can actually notice a tiny anomaly in the sound on the exact rpm you shifted up on, after downshifting and reaccellarating past that rpm (shortly after the upgear shift that is). Probably the gearshift event causes a suboptimal entry in the cached table for that particular rpm/load. It gets passed that suboptimal entry too fast to actually retrim is guess, but the effect is noticeable.
This "memory effect" only occurs in a short timespan, so the cache expiry time is probably short.

Rasputin

Sorry to go off-topic but :

Who the hell are you Barf??? Are you Leo???

Fabrice

Barf

That's me allright! I never manage to stay anonymous. ;-)

rkostolni

For those of us with a turbo, it would be great if we could tune closed loop so we could get rid of that crappy dongle. How difficult would it be to spoof the O2 sensor.

Rasputin

Hi Leo,

The <<Dutch RX-8 club webmaster>> gave it away a bit...

F

Tim Benton

So in closed loop, if we are wanting to try to get better gas mileage, we'd have to have some way of changing the target A/F ratios the PCM is trying to achieve. I don't think it's 14.7 to 1 since if that was the target, I think we'd be seeing better gas mileage. Has anyone logged just their normal driving, steady state cruising and since it's closed loop what A/F the car was hitting? If it's 14.7 to 1 or clsoe to it and people are still getting 14 to 18 mpg, then, well, that sucks *****.

So changing exhaust and intakes should actually make your mpg go down since if your in closed loop mode for 85% of your driving it's looking at your MAF and O2's and then trying to hit its A/F targets in the maps for it's throttle position and rpm...correct. IE, if you swap intakes and it does breath a bit better or change exhausts and the overall breathing efficency of the engine is better, the PCM can tell more air is being sucked into the engine by the MAF. It uses that new MAF voltage for the incoming amount of air and adjusts the fuel to hit it's target. That was the drawback with the FD, using the speed/density system and not MAF, it didn't know when you changed intakes or exhaust since it wasn't actually measuring the amount of incoming air, just a table of values based on the speed the car was going and the density of the air. Seems the MAF sensor in a NA car would be better suited to show minute changes depending on the calibration of the MAF to changes in air and the voltage it take to see that change.

Am I off here?

Tim

Rasputin

The PCM works in term of Lambda when it comes to AFR control. But you're correct, if you change the target values to run leaner, you'll get a better FE. And the target IS Stoich lambda (=1) or 14.x AFR.

No, your MPG should not go down in the area where it runs in closed loop. Although what you describe above is roughly correct, you need to think in term reduced intake and exhaust losses. For the same BMEP (actual power), you actually ran at a slightly lower load and therefore you bruned less fuel.

Fabrice

Tim Benton

So we know for sure the PCM is set to try to get a target A/F of stoich (14.x to 1) under closed loop? Is that something that had been logged by more than a few individuals for closed loop driving?

So if the PCM does have it's target A/F ratio of 14.x to 1 during closed loop, what's the deal with such crappy gas mileage. Does that debunk the myth that it the car was set up to run pig *** rich to save the catalytic converter and also the fact that some individuals were claiming they lost their engine to carbon build up? How could there be that much build up if it's running 85 to 90% (if not more) in closed loop mode.

Tim

sco

I've seen close to stoich for closed loop in more than one '8. It doesn't debunk the myth about pig rich... catalyst protection strategy typically will only kick in open loop where the PCM is typically not targetting stoich.

I haven't read the latest on carbon buildup.. can someone else summarise the latest theory?

Hymee

iTrader: (1)

Tim,

Lots of us have monitored the AFR and in closed loop they run very close to 1.0 Lambda (Stoich). Especially those of use with a sCANalyser

They do run too rich when under WOT or heavy load - i.e. open loop.

In closed loop on the highway at a steady 100 or 110 km/h, MAF v's Lambda v's VehicleSpeed logging shows about 9'ish litres per 100km fuel consumption in my experience.

Cheers,
Hymee.

zoom44

14 tp 18 is in town miles and is based on how much driving vs sitting you are doing, how quickly your car warms up(cold it is in open loop)how you accelerate and how you shift.

on the highway under light load the car is in closed loop hunting stoich and easily returns 24 mpg or better when travelling at 55-70 mph in 6th gear

the problems with engine seizing are in automatics that have 1 oil cooler that are in extreme heat areas(las vegas phoenix lubbock etc) and sit in traffic alot or never get revved above about 35k rpm. its an oil issue not a fueling issue. dont be suprised if all 2006 ATs come with 2 oil coolers in the US

Tim Benton

That is great to hear. I think I'm going to order the scanalyzer from Mazdaparts.com for the ***** and giggles and log some long drives and also city driving, etc just to see what our car is doing. So like mentioned above, doing the intake and exhaust, maybe possibly the high flow cat, would theoretically help us get better gas mileage and save a few pounds as well? Since it's breathing more efficiently and not need as much fuel for the same HP output?

Tim

Rasputin

The difference in FE will only be marginal and far from offsetting the cost of your intake and exhaust modifications.

Most modern petrol engines require heavy fuel enrichment at high engine speed, high load for catalyst protection. Changing catalyst for a better one won't change anything unless you re-map the original PCM with a higher catalyst temperature limt (presently around 960°C).

However, using scANalyser will show you where the engine runs in closed loop, where it goes really rich so you can learn how to drive economically when you wish to do so.

Cheers,

Fabrice