wfcall

There is some really great Info being brought forth here.

Silo does have a valid point. In open loop operation the stock ECU settings are aiming for something well under 14.7:1. when I go WOT before any mods the A/F always went to around 12.5:1.

Assuming these are stored algorithyms how does the ECU get long term feedback for self corrrection if the o2 sensor can ONLY tell the ECU that the A/F is above or below stoich; When the target A/F is well under stoich?

My observation proves; at least to me, that the ECU does learn in closed loop part throttle applications. I think every one agrees to that from what I'm seeing here.
I believe it learns in open loop too; I'm just not convinced how the system has the tools to do this.

Tony@Performance

iTrader: (16)

myth, but true.

It's a myth because there is no way the ecu can equalize or negate the power gains added by parts. if you add an intake and exhaust to the car, the ecu will not re-adjust itself back to stock HP etc....

But true, in the fact that the ecu is a self adjusting ecu. It's parameters are always changing, and the ecu is always changing settings, pulling timing when needed, etc....
nissan, subaru, and mitsubishi all have similar ecu setups

350Zenophile

iTrader: (20)

So wtf is closed and open loop?

'Closed Loop' is the term given to the ECU behaviour when the oxygen sensor signal is being used to largely control how much fuel the injectors are adding to the intake. The ECU works in closed loop most of the time - when the car is warmed up and idling, in constant throttle cruise - and so on. The ECU watches the oxygen sensor output and if the mixtures are getting a bit rich, it leans them off. If the mixtures are getting a bit lean, it richens them up. This causes the mixtures to fluctuate rapidly around 14.7:1 air/fuel ratio - what's called the stoichiometric ratio. The ECU aims to keep the mixtures at this number because its there where the cat converter works best at cleaning up the exhaust.

However, an air/fuel of 14.7 doesn't give the best power, so when you put your foot down, the ECU forgets about closed loop and goes instead into an operating system called 'Open Loop'. This just means that it ignores the output of the oxy sensor, instead picking the right amounts of fuel from its internal memories. Typically, the air/fuel ratio outside of closed loop might jump to 13:1, then 12:1 and then even richer still at 10 or 11:1.

The final typical operating approach is when the injectors are stopped completely - yes, they're actually switched off sometimes even when the car is driving along! This happens on the over-run - you're travelling along at 100 km/h, reach an 80 km/h sign and lift your foot. The ECU will then turn off the injectors until either you reapply the accelerator or the engine speed drops to near idle revs.

Like all things, these ideas apply to most cars - not all. Some Porsches, for example, stay in closed loop all the time - even when the mixtures are richer than 14.7:1. In other words, the oxygen sensor (a special one) is used to give mixture feedback to the ECU is all operating conditions. Other cars have a 'lean cruise' system, where on the open highway the mixtures will gradually lean out to say 15 or 16:1, so saving fuel. But for most cars on the road, the above approach is used.

350Zenophile

iTrader: (20)

Click on the first link

www.innovatemotorsports.com/resources/lm101.php

wfcall

I think when people say "negate power gains" some clarification is needed.

Assuming they self adjust;

Increasing the ability of the engine to move Air will obviously make it leaner before the ECU figures it out and gets A/F back to "target"

This temporarily lean A/F ratio before the ECU adjusts is where a lot of power gains lie. If you were able to adjust the A/F yourself on a stock engine to a "too lean" number you would also see a lot of power.

Maximum power always lies at an A/F ratio that is as lean as possible without detonation; The point of modifications is not to create a too lean condition it is to increase the ability of the engine to move air. The leaness created by these mods; even if temporary, is just a side benefit.

Even after the ECU adjusts to the "correct" A/F ratio the engine is still a better "air pump" due to the modifications because it IS moving more air and fuel for the same revolutions so there is a power increase remaining even though it is less than the initial gains produced by the TEMPORARILY lean conditions that existed before the ECU adjusted for the extra air it is seeing.

The ECU can negate a too lean mixture which is not what we were after in the first place.

The ECU will not negate the increased air moving efficency of these mods.

Therefore we would see a temporary spike in HP and then a decrease to a number lower than the spike and greater than the baseline.

HyperSprite

iTrader: (6)

Wouldn't the computer just take:

Air CFM multiplied times the map for manifold vacuum and intake air temperature = Fuel

If breathing mods add, say, 8% in breathing efficiencies, you are simply moving more air at lower revolutions.

Numbers just for illustrations (I have no idea what actual CFM is for this car)

Xrpm = Y cubic feet of air at WOT
Stock
2000 = 50
4000 = 100
6000 = 150

Add 8% breathing efficiencies

2000 = 54
4000 = 108
6000 = 162

So if the ECU sees 108 CFM at 4000rpm wouldn't it simply take incoming air of 108 calculate that with the vacuum table and air temperature table to decide how much fuel to squirt. RPM and throttle position would be unimportant in this calculation. So as long as you remain in spec for the totals the stock ECU is designed to deliver, it should be able to adjust for a few mods.

Chris

Brandon@Forged

So the real question...imo, is do the reflashes really work?

Another question...how do we go about getting around this?

Would a complete ECU replacement be necessary (and...the only way) to make real gains on mods? (I know this would be near impossible to do with the 350Z having a CAN system)

HyperSprite

iTrader: (6)

Maximum efficiency is best at most lean without detonation. Fuel economy is high here, power is not.

Maximum power requires a richer mixture, on most cars in the neighborhood of 13.5 to 12.5 to 1 (I have seen race cars get their maximum power at 11 to 1).

Even without detonation, if you were to run hard, say up a long grade at 14 to 1 or higher, you will see sluggish response and cooling problems.

Chris

Michael-Dallas

The ECU does not adjust for open loop operation. If it did, then it would be called closed loop operation.

The ECU runs rich in open loop operation because it's designed to be idiot-proof in open loop operation:

1- as stated before, narrow band O2 sensors aren't accurate given the condition (i.e. WOT)
2- the open loop WOT maps are tuned for the worst case scenario (i.e. if somebody runs WOT on 87 octane in 110 degree dry heat w/ the AC on and a heavy load going uphill) -- it's a Nissan one-size fits-all CYA

The ECU runs in open loop during WOT and during cold starts.

Here are a couple of things that need to be factored:

1- clogged injectors may require higher injector pulse
2- film accumulation on the MAS hot-wire may require more or less fuel

The O2 sensors are reactionary sensors that works w/ the other sensors in determining the optimal operating parameters after an engine cycle. Meaning, the ECU can not accurately calculate a/f (in closed loop operation) until at least one 4-stroke cycle has occurred.

Yes. My flash (not done by Technosquare) produced a solid 10rwtq throughout the whole power band w/o a/f tuning. There are other things you can tune besides a/f ratio (in the closed loop maps) such as throttle position, valve overlap, and the ever-so-popular ignition timing.

How does running 12.5:1 yield more power than 14.7:1? This may hold water if you run 12.5:1 w/ advanced ignition timing, but all things being equal, I'm not buying it.

Slightly off note: in one an SAE article published by Nissan, they say state that an engine produces more power w/ light detonation. I will see if I still have that article.

Michael.

350Zenophile

iTrader: (20)

OK...first off this article is a must read to participate further in this topic. It alone should save us about 18 pages of covering the basics of AFR tuning: Tuning Air/Fuel Ratios

Michael-Dallas - Who did your reflash and was it on a VQ35?

Michael-Dallas

Check your pm.

Michael.

HyperSprite

iTrader: (6)

It looks interesting to bad I am not a subscriber. Can you sum up what it said in the rest of it? I am very interested but to cheap to pay for it.

Chris

HyperSprite

iTrader: (6)

Even a simple carb and vacuum advance distributer is more complex than your above ECU scenario.

Open or Closed the ECU needs to know how much air is going into the motor. Low RPMs at WOT draw much less air than high RPMs at WOT. The ECU needs to know the density of the air going into the motor or a car set up at sea level would run terrible at high altitudes. Even if it is not using O2 as a variable, the map can still be trimmed based on what it reads during closed loop operation. So clogged injectors and whatnot can be compensated for through out the range of use.

Quote:

Yes. My flash (not done by Technosquare) produced a solid 10rwtq throughout the whole power band w/o a/f tuning. There are other things you can tune besides a/f ratio (in the closed loop maps) such as throttle position, valve overlap, and the ever-so-popular ignition timing.

How does running 12.5:1 yield more power than 14.7:1? This may hold water if you run 12.5:1 w/ advanced ignition timing, but all things being equal, I'm not buying it.

Slightly off note: in one an SAE article published by Nissan, they say state that an engine produces more power w/ light detonation. I will see if I still have that article.

Michael.

I have not read the Nissan article personally but I am almost positive it is talking about timing.

The ignition timing should always be a hair shy of detonation, how much buffer a car company gives it is their prerogative but having efficient knock sensors located in a few key places allows this "right on the edge" tuning. In lean, no load conditions, fuel is burning slowly so lots of advance needs to be dialed in so the actual expansion of gasses occurs in the earliest possible moment without knocking. Richer mixtures require less advance because of the faster flame front but it should still be as early as possible without knocking.

Chris

Silo

iTrader: (1)

Here's your answer - figures can vary by a few tenths for various engines:

Silo

iTrader: (1)

Please everyone understand:

"closed loop" = ECU using O2 sensor input
"open loop" = ECU ignoring O2 sensor input

Nothing more, nothing less! It appears by reading some statements that some people confuse the closed/open loop meaning and/or believe that in "open loop" operation the ECU ignores all other sensors too (e.g. MAF/MAP, knock, coolant etc sensors). This is NOT the case.

Open/closed loop refers exclusively to the input of the O2 sensor!

Z BOY

iTrader: (41)

nice diagram.

wfcall

Assuming that in open loop the ECU is factory tuned for worst case scenario which means that at wot the a/f is around 11-11.5 to counter high heat/crap gas situations. I say that it is because the wideband in our car read/logged around that number before ANY mods were made.

In that case adding a few breathing mods is going to move the a/f towards optimum power on the graph above.

When I said leaning one out makes more power I was not refering to making it leaner than stoich; I was refering to the a/f that the ECU aims for at WOT being a little richer than optimum because

350Zenophile

iTrader: (20)

I didn't realize you needed to be a subscriber?

I just Googled "Air Fuel Ratio Tuning" and that was one of the top links. Try refreshing your browser or using this link:

http://www.autospeed.com/cms/A_1595/printArticle.html

Mr B

iTrader: (2)

If you guys have any questions regarding how the ECU works, call me at Technosquare.
And yes, there is no open loop in our ECUs.

wfcall

The nissan service manual clearly states in the ECU section on page EC-26 that there is an open loop feature and also a self learn feature.