Do These Afr's Look Correct?

[ascenion24]

Finally hooked up my Techedge wideband today. At idle it was reading 14.5... good enough for a start.

Reving the engine at idle saw it move down between 12 and 13.

But if I reved the engine hard, when I released the throttle as soon as the revs start to die the AFR would go extremely lean for about half a second or so. And as it came to idle the AFR would return to normal.

Heres a snapshop of the data logging.

Is this normal? Im thinking when the engine is revving hard and the throttle is closed, the MAF sensors the less air so it reduces the amount of fuel injected as its designed too. But because theres this big pathway through the intercooler and all that piping, a decent amount of air still gets suck through, but now with no where near enough fuel hence the lean reading.

Edited February 18, 2010 by ascenion24

[MBS206]

Perfectly normal, and it's the ECU turning the injectors off when you drop the throttle.

[ascenion24]

Thought so, just double checking.

[ascenion24]

I wonder if it looks like this from the factory, I highly doubt it.

The ecu would know there is x amount of time before the air it senses at the MAF gets to the cylinders, and its this time delay that would be factored into the ecu for the firing of injectors.

The fact that my skyline now has a big front mount, extra piping, its creating extra lag from the MAF to the cylinders, and the injectors are reacting too early.

Does anyone know of such a setting in the ECU that can be changed? This is definitely something I would like to fix up.

[MBS206]

I wonder if it looks like this from the factory, I highly doubt it.

The ecu would know there is x amount of time before the air it senses at the MAF gets to the cylinders, and its this time delay that would be factored into the ecu for the firing of injectors.

The fact that my skyline now has a big front mount, extra piping, its creating extra lag from the MAF to the cylinders, and the injectors are reacting too early.

Does anyone know of such a setting in the ECU that can be changed? This is definitely something I would like to fix up.

For what? It's perfectly fine...

Ignore the AFR at idle, air flow is way too slow to be measurable properly.

My AFRs without revs moving, without timing or ignition moving, will swing ont he LM1 from 13 - 15.8:1 but the motor doesn't even change sound.

Low air velocity, large pipe.

[JonnoHR31]

the ecu cuts fuel under decel, the engine becomes an air pump during this time and AFR's will spike to over 20:1. perfectly normal and nothing to worry about

[ascenion24]

Yeah your right Jonno, apparently its there for fuel saving, the fuel doesn't cut back in till around 2000rpm or so. You can set it lower to round 1200 to save more fuel but apparently if you do this to an auto you get some more problems due to torque converting locking/unlocking.

I've found the settings in nistune so going to have a play with it.

[lachlanw]

there is a reason cars dont have these from factory . its called TOO MUCH f**kIN INFORMATION. were you perfectly happy untill you put the gauge in and got worried about this ?

[JonnoHR31]

Yeah your right Jonno, apparently its there for fuel saving, the fuel doesn't cut back in till around 2000rpm or so. You can set it lower to round 1200 to save more fuel but apparently if you do this to an auto you get some more problems due to torque converting locking/unlocking.

I've found the settings in nistune so going to have a play with it.

where it cuts back in depends on the speed the engines moving back towards idle. just lower it until it makes the car drive like shit and stalls. the only problem i found with having it too low in a manual car was on extremely light throttle down a hill in 5th it'd cut in and out sometimes, but thats a tps issue aswell

[ascenion24]

lachlanw, that would have to be one of the stupidest comments I've heard in a while.

You might as well say, hey I've made all these mods to my car, and it runs fine, but I wont worry about tuning it because theres obviously nothing wrong.

I'm sure you were just trying to get your post count up so ill disregard what you said.

[D_Stirls]

FYI

The factory ECU does have decel' fuel cut.

[ascenion24]

D Stirls, are you sure on this?

I've been told that it does.

I need to get a registered copy of nistune so that I can look into the files to see for myself.

But if indeed it doesnt then thats more of a concern because then I have an actually problem more along the lines of what I first thought that I need to fix.

[D_Stirls]

D Stirls, are you sure on this?

I've been told that it does.

I need to get a registered copy of nistune so that I can look into the files to see for myself.

But if indeed it doesnt then thats more of a concern because then I have an actually problem more along the lines of what I first thought that I need to fix.

100% sure

[ascenion24]

Dstirls, I've had 3 people tell me they are positive it does have fuel cut. One of them has played with it them self on Nistune.

So you must of got feed some bad information.

[GTR1993]

loling that u are both sating the same thing yet arguing about it.

[D_Stirls]

I just figured that, no argument here.

[Cowboy1600]

lachlanw, that would have to be one of the stupidest comments I've heard in a while.

You might as well say, hey I've made all these mods to my car, and it runs fine, but I wont worry about tuning it because theres obviously nothing wrong.

I'm sure you were just trying to get your post count up so ill disregard what you said.

I think what lachlanw was saying was not at all stupid. He's essentially saying "if it ain't broke, don't fix it."

You've had a few people tell you that it's perfectly normal and it should be left alone yet you are insisting on changing it for the sake of changing it. If you didn't look at the data you wouldn't know it was doing it, so why change it.

And your example of not tuning a car that has been modded is piss poor. It might run fine but as we all know an improper tune can damage engines. It would seem this is NOT the case with the fuel cut on deaccel, so why screw with it?

Just sayin'....

[MrStabby]

I think what lachlanw was saying was not at all stupid. He's essentially saying "if it ain't broke, don't fix it."

Or you could interpret what he said as "Dont ask questions and learn stuff". The OP asked "Is it normal?" not "How do i fix it?".

[ascenion24]

Dstirls sorry, I read over your post too quick and thought you said that it doesn't have fuel cut.

"it's perfectly normal and it should be left alone yet you are insisting on changing it for the sake of changing it"

thats like saying your spark advance is perfectly normal, no need to change it.

Anyways I'm sure we could sit here and go back and forth and turn this into a stupid discussion but I'm sure everyone is on the same page, we know why the car does this, we have learnt about it were all smarter for this and if you want to f*ck with it its up to you.