Does BOV affect air fuel ratio?

[lambo]

Anyone knows about those return BOV that vent gas back? and the above post also

[greygirl1976]

bov that vent to atmos DONT change air fuel ratios on cars that only have afm ie sky,silvia coz were the factory plum back go to is between turbo and afm. So the afm doesnt register it .2 i built a rb20t in a silvia in qld with a turbosmart type 2 bov for a customor in sydney and he went to the rta to get it tested on emission and it passed with flying colours with the bov type 2 on it remember it goes pod filter afm factory bov inlet pipe turbo

[ANDY32]

Greygirl1976 what colour is the car that you built that passed the NSW RTA tests? I go down there every two weeks and i would like to see it. My mate is STILL waiting for you to post where S.B.performance is so he can go and look at your conversions. I see you reply to everyone else we want to give you work but we would like to see some of your work before we part with any cash. Want is the guys name or his rego number so i can see his car (the one down south).????????????

[xRHETTx]

Lambo, will try to answer ur questions, but im no expert. (dont even have a turbo car yet)

Originally posted by lambo

Does those BOV that vent excess air when the throttle is shut affect the air fuel ratio?

Yes, when the excess air is vented to atmosphere, a similar volume of air is sucked in through the filter, and through the air flow meter. The air flow meter (AFM) tells the engine to inject heaps of fuel to make up for increased volume of air. Therefore AFR goes rich and car puffs smoke and maybe even stalls.

Since the throttle is shut the air getting into the engine should be the same even without the BOV.

Its not the volume of air getting 'to' the engine thats important, but the flow through the AFM. When throttle is shut, no air (little air) is getting to engine. With no blow off valve or with a plumb back type BOV, air is recirculated back into intake, after the AFM, therefore making no difference to AFRs.

Isn't the job of the BOV is to pretect the intake turbine from blow back pressure from shutting the throttle abruptly.

Yes.. and it does. Both plumb back and atmo venting BOVs do this.

Hope that helped,

Rhett

[greygirl1976]

BLOW OFF VALVES DONT change air fuel ratio coz the blum back is after the afm go and have a look under the bonnet of a skyline turbo and u will see that the blum back is after the AFM .remember the afm only registers air goin one way

[raist60]

They are talking about an atmo venting BOV, which stuffs up a/f ratios.

[greygirl1976]

Originally posted by greygirl1976

BLOW OFF VALVES DONT change air fuel ratio coz the blum back is after the afm go and have a look under the bonnet of a skyline turbo and u will see that the blum back is after the AFM .remember the afm only registers air goin one way

even ones that vent to atmosphere it dont change a.f ratio

[raist60]

umm yeah they do, just give up your wrong, k. the air dumps straight out after afm saw it, ecu gives fuel for air that has since been dumped to atmo, hence riching up your mixtures something bad.

[greygirl1976]

Originally posted by raist60

umm yeah they do, just give up your wrong, k. the air dumps straight out after afm saw it, ecu gives fuel for air that has since been dumped to atmo, hence riching up your mixtures something bad.

u just said it after the afm thats correct so how does the afm register the air when the plum back is after the afm its simple it dont coz its after the air flow meter

air goes throu pod filter throu afm them meets up with plum back pipe is then in to turbo does everyone understand now or do i have to draw u a picture?

[DAMQIK GTS-T]

greygirl1973 maybe I can explain why raist60 is right,

With a atmo ventventing BOV the Afm has accounted for the fuel going into the motor, but not for it getting dumped to atmo thats why a atmo venting BOV will richen up the mixtures on a throttle release, this is however not harmful for the engine as it only happens for a moment it has been known to cause minor flooding of the engine causeing it to stall.

[greygirl1976]

thats y u have a tps {throttle position sensor} and a oxygen sensor to compensate for this

[GiJOr33]

Mine only stalls if i go about 1-20km/h and slam on the anchors to stop quickly. Stalls maybe 2 times a month tops.

Check out this thread dude... maybe you have this problem if your car stalls when you jump off the gas and onto the brakes. Something to do with the fuel pump ground wire...

http://www.skylinesaustralia.com/forums/sh...s=&threadid=408

Cheers,

Andrew

[raist60]

hahaha, are we trying to re-write the laws of ECU physics or something here. Just give up man. Please for your sake. We can argue all day long but we are still right, serious dude we arent lying

ATMO BOVs make rich A/F ratios when venting... ECU has accounted for air it expects to end up in cylinder so adds fuel for air that has since been expelled through an ATMO BOV. Ie the fuel gets dumped but the air never made it into cylinder therefore higher fuel ratio to air, therefore lower A/F Ratios. Hoora!11

[greygirl1976]

Originally posted by raist60

hahaha, are we trying to re-write the laws of ECU physics or something here. Just give up man. Please for your sake. We can argue all day long but we are still right, serious dude we arent lying

ATMO BOVs make rich A/F ratios when venting... ECU has accounted for air it expects to end up in cylinder so adds fuel for air that has since been expelled through an ATMO BOV. Ie the fuel gets dumped but the air never made it into cylinder therefore higher fuel ratio to air, therefore lower A/F Ratios. Hoora!11

ok time to talk technical

raist60 as u dont understand what im talkin about ive just learnt about this at tafe {yes im a mechanic} ok here goes

all fuel injected cars run lean when u snap the throttle off. The tps tells the ecu to shut off fuel to the injectors only for 1/100th of a second to allow for the excess fuel to burn off in the engine as this is happening the oxygen sensor is reading the exhaust gasses and tells the ecu what is goin on as soon as the o2 sensor sences a weak mixture it tells the ecu to flow more fuel so when a bov vents to atmo or not it discludes that air coz the tps has told the ecu to shut fuel off which in turn runs the engine lean

if u dont beleve me take your car to a automotive workshop and do a test on the gass anailzer with a bov plumed in and a bov venting to atmo u will see it for yourself these computers r allways learning {called fuzzy logic} all fuel ratios r controled by the o2 sencer

[GiJOr33]

But what about the Air Flow Meter? you didn't mention that... and if that plays no part in it, why do we have them?!?!

And why is it that when you see a turbo car with an atmo BOV racing, it blows black smoke on the gear changes?

If the air that is already measured by the air flow meter and the signal is then passed on to the ECU so it can inject the right amount of fuel, then when the air is not there to burn with the fuel as it's been vented, then you'd expect more fuel/less air... richer mixture for that point. Maybe like you say the computer stops the fuel being inject the instant the throttle is closed, but what about the air that was measured before the it was closed?

Andrew

[DAMQIK GTS-T]

gerygirl1976

Yeah, Where is the AFM in your exellent but incorrect (when applied to skylines anyway) explanation?

You may need to go back to tafe and recover the module on efi and fuel mixtures.

ok time to talk technical Are you sure what you said isn't applied to a map type efi only? because what you said dose sound correct for map sensor efi.

To take the point one further, I have perviously fixed the stalling due to overrich with an atmo bov problem by adjusting the air bypass valve at the back of the inlet.

[greygirl1976]

the turbo cars racing blowing a puff of black smoke r soo fuelld up with too much fuel to start off with my car does this and i dont have a bov on my car and as for the afm

it plays its part but when the throttle is snaped shut the computer kinda ignores the afm for an 1/8th of a second coz theres all this fuel in the engine but no air comming in{throttle is shut} so the ecu stuts off the injectors for that 1/8th of a second to burn off the fuel and the air in the plemun chamber then when the o2 sensor senses that the excess fuel has burnt off the o2 sensor tell the ecu that the engine is very lean and turn the injectors back on and at the same time starts talkin to the afm

all the above happens in less than second

if u stick a sniffa up the exhaust and do this as soon as the throttle is snapped shut the anlizer screen spikes to the rich scale about 12to13-1 for 1/8 of a sec then leans out to about 17to18-1 and the scale flattens out back to 15to 14.7to1 this all happens in under a second providing the car isnt runnin rich to start off with all the above happens the same way even with a na motor do u need me to explain more

and im not trying to b a smart ass im trying to help so every 1 can understand what goes on

[DAMQIK GTS-T]

Mate I run A Link Lambda on my car and before my new ecu it stayed rich for more than 2 sec on back off (blow Off Venting to atmo) on the dyno it run so rich it was off the scale 10:1 and richer.

By what you are saying the ecu ignores the afm for

1/8 of a second well it takes longer than that for a bov to dump to atmo therfore the mixtures could go rich.

it takes 1/8 of a sec for the pressure to build high enough for the bov to open.

most ecu's only sample every 1/8 sec or 125ms

You are not correct with what you are saying Sorry...

[GiJOr33]

and aren't most O2 sensors either hi/low reading??? used mostly for the warm up period? wouldn't you'd need a wide band O2 sensor to read the air/fuel mixes properly... and as these are expensive i wouldn't have thought they'd be a factory item.

[DAMQIK GTS-T]

thats right they only read between 12 - 14 or so, and only once the motor is hot enough,

A wide band O2 sensor is around the $500 mark

Hey Theres another reason why the ecu cant use the O2 sensor as described by gerygirl1976 the signal would be out of range the factory ecu only uses its signal during cruse mode not throttle on or throttle off.