Question about BOV and fuel mixtures.

[LANFOH]

G'day all,

I was just wondering....... if I install an air/fuel controller ie SAFC with an atmospheric BOV and have it tuned accordingly will the mixtures still run rich due to the air flow meter being tricked by the BOV? Is this also the case if I have my car tuned with a Power FC?

Any response would be appreciated.

Cheers

[joh21m]

how are ya? got this of nengun website, hope it answers ure question...

The second-generation S-AFC is a fuel computer that adjusts fuel/air ratio by modifying the air-flow meter/MAP sensor signal. The S-AFC features a user-definable, eight-point, adjustable fuel curve that can be set in 500 RPM increments. The range of fuel adjustment is +/- 50% at each of the user-defined setting points. On hot-wire vehicles, the Deceleration Air Flow Correction function is capable of curing the erratic idle and stall problems associated with open-atmosphere blow-off valves on hot-wire air-flow meter systems. The S-AFC is capable of monitoring and replaying the following data channels in Numerical, Analog Meter and Graph displays: Intake Manifold Vacuum/Boost Pressure, Air Flow Capacity, Intake Manifold Pressure, Karmann Frequency, Engine RPM, Throttle Position, and Air Flow Correction %.

[joh21m]

actually i just read ure post again and it doesnt really answer ure question, lol, but im guessing it would fix ure problem...

[LANFOH]

Thanks for the reply mate, I think it sort of answers my question but I think even if you tune the mixtures to certain rev ranges the atmo BOV will still trick the standard computer that the throttle is still open, but I dont really know...... I think the go is simply fitting a plumb back BOV.

:headspin: :headspin: :headspin: :headspin: :headspin: :headspin: :headspin:

[R33vit]

SK mentioned how they get the backfire out of their cars by leaning out the mix near idle and advancing some timing.

Do a search for it..

[LANFOH]

cheers

cant really find the answer tho

[geno8r]

I was just wondering....... if I install an air/fuel controller ie SAFC with an atmospheric BOV and have it tuned accordingly will the mixtures still run rich due to the air flow meter being tricked by the BOV? Is this also the case if I have my car tuned with a Power FC?

You'll only run rich for a second until you open up your throttle again & then the airflow calculations will be correct again. Its nothing bad or dangerous, but may be annoying because you'll get stalls easy after venting out your BOV. I had to change my driving style 'tap the throttle after venting the BOV' to stop stalls.

[LANFOH]

You'll only run rich for a second until you open up your throttle again & then the airflow calculations will be correct again.  Its nothing bad or dangerous, but may be annoying because you'll get stalls easy after venting out your BOV.  I had to change my driving style 'tap the throttle after venting the BOV' to stop stalls.

Thanks for the response mate, you are right it is the the stalling that annoys me especially when you lose the power steering.... so I have also adjusted my driving style accordingly, however I would rather drive without bliping the throttle (after venting). So even with a safcII and mixtures tuned, you will still run rich for a moment and stalling will still occur? If so I think I will change my blow off valve to a plumb back before I install my A/F controller. Do you know if this would occur with a power fc and atmo BOV?

[geno8r]

Thanks for the response mate, you are right it is the the stalling that annoys me especially when you lose the power steering.... so I have also adjusted my driving style accordingly, however I would rather drive without bliping the throttle (after venting). So even with a safcII and mixtures tuned, you will still run rich for a moment and stalling will still occur? If so I think I will change my blow off valve to a plumb back before I install my A/F controller. Do you know if this would occur with a power fc and atmo BOV?

Yeh I'd imagine there wouldnt be any difference with the power fc, you'll still get stalls with an atmos BOV. You'll be fine with a plumback so just get one of those if it suits ya.

Only way to fight the stalls with atmos BOVs i believe is with a SAFCII. I actually have one of these, got it dyno tuned but i dont think the feature which is meant to help stop stalls with atmos BOVs has been tuned. There might be that function on the Power FC too?

I think the question would be to find somebody who actually has that feature on the SAFCII tuned & working!

[LANFOH]

Yeh I'd imagine there wouldnt be any difference with the power fc, you'll still get stalls with an atmos BOV.  You'll be fine with a plumback so just get one of those if it suits ya.

Only way to fight the stalls with atmos BOVs i believe is with a SAFCII.  I actually have one of these, got it dyno tuned but i dont think the feature which is meant to help stop stalls with atmos BOVs has been tuned.  There might be that function on the Power FC too?

I think the question would be to find somebody who actually has that feature on the SAFCII tuned & working!

Might just get a plumb back, bit sick of the sound my atmo makes anyway.... too loud.

Thanks again

[Sydneykid]

You can do it with an SAFC but is it is very tricky and doesn't always work. This is because you have no control over ignition timing and that helps to hold the idle. Power FC's have adjustable idle speed as well, so you can add a few rpm which helps.

[Dr_GTST]

did any of you guys notice poor fuel economy with an atmospheric BOV?

[Sydneykid]

did any of you guys notice poor fuel economy with an atmospheric BOV?

Not me, the "richness" is only for a tenth of second. Just enough tot stuff up the return to idle, but not really very much compared to the fuel you use in normal driving.

[WiZardOz]

I was plagued with the stall and unstable idle problem prior to my PFC upgrade

PFC doesn't seem to have problems with the atmo BOV on my car, altho my set-up is a little different to most with the stock re-circ BOV not being removed when the atmo BOV was added (don't ask me .. the car came from Japan like that). But I am happy because I don't have the huge 'Pssstttt' sound when it vents, as I see it it's assisting the standard BOV to vent quickly ( I could be wrong .. wouldn't be the first time

If it ain't broke don't fix it is my motto... so I have not bothered to remove the standard BOV

[USRB25S13]

Not me, the "richness" is only for a tenth of second.  Just enough tot stuff up the return to idle, but not really very much compared to the fuel you use in normal driving.

My car is running the stock BOV plumed back into my intake. When I shift from 2 to 3rd or 3rd to 4th I get what feels like lag but my boost is @ full boost (14 PSI) the car takes a second (more like 1/2 second) then it takes off. I am getting very rich readings on my A/F moniter. Since it only reads 10.1:1 I don't know how rich it gets but I feel this overly rich condition is why my car bogs between gears. I have even tried flat shifting but the A/F's still get rich. There doesn't seem to be anything I can do with the PFC to correct this. Is there an electronic device that will solve this problem?

[Sydneykid]

My car is running the stock BOV plumed back into my intake.

I assume that means it returns the air between the AFM and the turbo.

When I shift from 2 to 3rd or 3rd to 4th I get what feels like lag but my boost is @ full boost (14 PSI)

That's impossible, the BOV has vented the pressure. Either you have a very slow reacting boost guage or the BOV is not venting properly.

the car takes a second (more like 1/2 second) then it takes off.

That's a very long time, there is some delay in all cars, but 1/10th second is more like it.

I am getting very rich readings on my A/F moniter.

How fast is the lambda sensor? I have yet to find one that is accurate at 1/10th second.

Since it only reads 10.1:1 I

Sorry I don't understand what this means

don't know how rich it gets but I feel this overly rich condition is why my car bogs between gears.

10 to 1 is not overly rich, that's what it would run standard.

I have even tried flat shifting but the A/F's still get rich.

They should be no richer than when it is running at those rpm's. Do you have a dyno graph of the A/F ratios?

There doesn't seem to be anything I can do with the PFC to correct this.

What have you tried so far? We have 5 cars running PFC's (from 225 rwkw to 415 rwkw) and none of them have this problem.

Is there an electronic device that will solve this problem?

I don't even know what the problem is for sure. But I suspect it's either the basic setup of the PFC (injector lag maybe) or the tuning.

My best suggestion, post up a dyno graph of the A/F ratios, power and boost curve. Then list out alll the mods. There are plenty of smart guys on here with lots of Skyline experience, if we have the necessary data I am sure one of use will know the answer.

[USRB25S13]

I assume that means it returns the air between the AFM and the turbo.

That's impossible, the BOV has vented the pressure.  Either you have a very slow reacting boost guage or the BOV is not venting properly.

 

That's a very long time, there is some delay in all cars, but 1/10th second is more like it.

How fast is the lambda sensor?  I have yet to find one that is accurate at 1/10th second.

 

Sorry I don't understand what this means

10 to 1 is not overly rich, that's what it would run standard.

They should be no richer than when it is running at those rpm's.  Do you have a dyno graph of the A/F ratios?

What have you tried so far?  We have 5 cars running PFC's (from 225 rwkw to 415 rwkw) and none of them have this problem.

I don't even know what the problem is for sure.  But I suspect it's either the basic setup of the PFC (injector lag maybe) or the tuning.

My best suggestion, post up a dyno graph of the A/F ratios, power and boost curve.  Then list out alll the mods.  There are plenty of smart guys on here with lots of Skyline experience, if we have the necessary data I am sure one of use will know the answer.

Ok. Lets start with the setup.

I have a T3/T4 56 trim stage 5 wheel. Turbo mounted on the stock manifold with adaptor box for external wastegate.

Motor is a series II RB25DET

Apex PFC

Q45 MAF

S15 injectors (What should the lag settings be?)

Nismo FPR Pressure is set at 38 psi @ idle under vacum.

Walbro high flow fuel pump.

3" turbo back exhaust (no cat)

17X9X3" FMIC.

Running 14 PSI

Car when 13.0 @ 112 running 12 psi.

For my wide band I have a tec edge (not sure what model but it's the older one)

I noticed even when I am not running the car hard between shifts my A/F goes right and peggs the meter. The meter on goes down to 10:1. I have the car street tuned to run 11.5:1 or richer. See very little knock on the moniter (only jumps to 25-28)