A/F Question

[whooppee777]

I've noticed on my blitz rvit that when i am driving the a/f normally stays around 14 but when i come up to a stop sign or stop light and i pull the car out of gear and into nuetral to coast the a/f jumps up to 17 and stays there till i hit the brake or go back into gear. is this normal?

[cali yaris]

hitting the brake changes your air/fuel ratio while in neutral? hmmm.

[CASTREX]

It could be some kind of fuel economy feature...

[largeorangefont]

Yes the car is just saving fuel at idle conditions. I wouldn't worry about it.

[Tamago]

17:1 should throw a CEL though.. well at least it does in my car :(

[Nexus1155]

DFCO leans AFR on coastdown/stop for economy i suppose that is happening? Might want to read more on it, it activates different in different cars..

[whooppee777]

hitting the brake changes your air/fuel ratio while in neutral? hmmm.

just reporting the facts and not just in neutral but also when i take my foot off the throttle completely while still in gear too. my guess is it has something to do with vacuum.

Yes the car is just saving fuel at idle conditions. I wouldn't worry about it.

thats what i thought too but y does it change when i hit the brake? if it were something bad it should set a CEL. so until it does i'm not worried.

does the scan gauge 2 give a/f readings? if so can someone with a near stock yaris or near stock yaris let me know what it reads under these same conditions?

[cali yaris]

I don't think the scangauge does a/f. I know the blitz r-vit does -- whoopee didn't you have one of those installed at one point?

[turboyaris]

its not uncommon for an AF to read 17:1 when the engine isn't under any loads. if there is no real load on the engine, the likelyhood of detonation is less, not too mention, that detonation would happen around the same time as ignition spark anyways, as the timing as adjusted too... at least this is what I have been told. It more has to do with the throttle being closed and all then hitting the brakes I presume. Is your car manual?

I know on my tune, when I accelerated it was tuned to 12:1, then if i was just cruising at speed it was around 14:1 and as you said it went above that for idle and no load situations. The reason I was told is also to clean the plugs and engine out as I guess it burns any reminant fuel that hasn't already been burned off.... if that makes sense

[whooppee777]

I don't think the scangauge does a/f. I know the blitz r-vit does -- whoopee didn't you have one of those installed at one point?

i have the r-vit. i know not too many others do. i know more people have scangauge 2 but not that it matters considering it doesnt read a/f

[richardholdener]

The reason the A/F ratio changes under decel is that the injectors are switched off completely under this condition. They are switched back on to keep motor from stalling and keep idle stable. The idle air/fuel should be 14.7:1. Toyota does not run leaner mixture at idle (emissions reasons).

[whooppee777]

excellent. i am completely worry free now. thanks richard

[cali yaris]

when i come up to a stop sign or stop light and i pull the car out of gear and into nuetral to coast the a/f jumps up to 17 and stays there till i hit the brake or go back into gear.

it's the hitting the brake part that I still don't get. I understand DFCO conditions.

[whooppee777]

what the hell is DFCO?

[whooppee777]

Deceleration Fuel Cut Off. It is a fuel economy feature.

http://www.yarisworld.com/forums/showthread.php?t=4248

then in that cae...

I am assuming when he is applying the brake he is below 1000 rpm, so DFCO is gonna is gonna quit and he will see normal conditions on his a/f readings. When he puts his car back in gear again I am assuming he is hitting the gas which also will stop dfco.

Gotta love assumptions. Maybe whooppee can shed some light.

yes rpms below 1000 when braking and yes hitting the gas when putting into gear.

good to know my dfco is working properly

[whooppee777]

i dont know how to get the r-vit show mpg. i see fuel economy in the menu somewhere but it needs to be configured some how i guess buuuuut the manual was in japanese. so shit