i had a BOV vented to the atmosphere and the car ran like junk. stalled at stop lights and idled funny. put stock one back in and much better. im going to get a BOV but re direct it back into the intake.

also my gas millage was very very bad with the BOV that dumped into the atmosphere.

 

That's interesting .... anyone else having similar problems?

Also, what do you consider bad gas mileage?

 

what blow-off valve were you using?

 

i would rather not say, but it was the same problem with another model also. anything that dumps back into the atmosphere the ecu already calculated the air fuel mixture for that air and now its missing when it goes back into the atmosphere so it needs to make up for it by adding more fuel.

gas mileage was like really bad. under 250 miles per tank

 

I had the same problem with my DSM but all I had to do was block the up where the air went back into the intake (with a rubber plug) and it ran fine. It also depends on the BOV, some have stiffer springs and some have lighter springs, and it has to be just right.

And yes, I got under 250miles/tank when I had my BOV VTA but it was well worth it, the sound is amazing!

 

That's bad??? I don't think I've got 250 on ANY tank yet! Usually around 210-220.

 

That's right around what I'm getting as well. No BOV though. This is what I have so far:

- Buschur 3" tubro-back w/ test-pipe
- Bushcur intake
- S-AFC - w/ Buschur settings
- Profec B spec - set at 21psi
- Blitz TT
- Boost and A/F gauges

 

So you mean you're getting 250 or 210-220? Did you notice any increase in gas mileage after leaning out your A/F with the S-AFC, assuming driving habits remained the same?

 

Oh my bad. 210 to 220 on 94 octane. I run high RPMs a lot though. It's kinda hard to find a happy medium, change gears and RPMS are too low, leave it and the RPMs are high, but our Evos love high revs and sitting in the high RPMS.

Didn't notice change in MPG after I added the S-AFC. Definitely quicker though. Seems to still run a bit rich but not as rich as stock. Better a little rich than lean.

 

I got to 260 miles once!! ONCE!! That was mainly highway.. I have yet to take it on a long highway trip though...

 

Rich is always good.

 

I'm assuming you're either being sarcastic or talking from a purely safety standpoint in which rich is good, but otherwise it's a power killer and gas guzzler, though admittedly less of a power killer than too lean which blows your engine .

 

An AFC will only really affect wide open throttle running.

There are two modes of operation in the ECU. One is closed loop, where the ECU adjusts the injector pulse-width according to feedback from the O2 sensor. This is what is being used at idle, cruise, light throttle, etc. The feedback from the O2 sensor means that tuning any piggyback like an AFC while in closed loop mode will do absolutely nothing to the closed-loop air to fuel ratio. The ECU will merely adjust its fuel trims to get the O2 sensor voltage back where it wants it. Ok, it isn't that simple, but that is the general idea.

Open loop mode is entered when the the engine is in a high load situation. Opening the throttle 100% will do this. So will going over a certain RPM. So will a certain airflow number. The ECU disregards the O2 sensor in this case. So it goes purely off the maps in its memory. The AFC can and will affect the air to fuel ratio in this case, and there is nothing the ECU can do about it.

Considering that very little time is spent in open loop mode compared to closed loop mode, closed loop mode is more likely to affect your fuel milage. And we already determined that an AFC won't affect closed loop mode. So it (and any fuel related modification) is unlikely to affect fuel milage much at all.

What will affect your fuel milage is opening up the intake and exhaust to get the engine to breathe better and reduce pumping losses. This tends to increase highway milage, but decrease city milage. I get 31mpg on the highway, but only 18mpg around town.

 

Also, venting a BOV to atmosphere is a bad idea! A BOV is set up to open while the intake manifold is under vacuum. This means that when you are cruising along, the BOV can be open, sucking air INTO the intercooler pipe that it is mounted to. If your BOV is vented to atmosphere, this means you are sucking UNFILTERED AIR into your engine! Don't do this!

 

crap, my car is running messy... idling odd, close to stalling like you said...other people had the same BOV... but had no problems... can I redirect this back and make it recirculate ??? Please reply, need help

-Shahul