I know, I don’t listen, I have to learn things the hard way. I've had a GFB 50/50 hybrid BOV(the first gen with no adjustment screw) on since the car had about 1000 miles on it, I'm close to 5000 now. I got it for a killer deal from Onizuka so I figured it was worth it for a little rice on my car, and a cool sound. I always noticed a slightly rough idle, it always backfired between shifts(and I don't mean the sweet cackle, I mean KABOOOM backfire), as well as a real mild idle search(you could see the rpms moving around a little at idle since I put the BOV on. I recently paid a visit to gruppe-s to have helix front and rear sways as well as end links installed along with group N motor, tranny, and pitch stop mounts. I left gruppe and noted the car felt completely connected and absolutely wonderful, albeit a bit louder, especially the tranny in the lower gears, aside from the extra NVH the car was wonderful. I lucked out and just had one stop sign that I pretty much rolled through and a green light until right before the highway when I got stuck at a light. HOLY CRAP this thing felt like utter crap. It was idling like a diesel truck. Really hard rough idle, but I could feel that it was the same rhythm as before, just much harder. I didn't notice anyone with this type of comment after installing the mounts so I was sure something was wrong. I looked at my blitz DTT(installed more for the boost gauge than TT) and it was happily sitting around -.62 which was what it used to be, so no vacuum leaks. WTF is wrong with my car. I battled the dreaded 880 commute back to San Jose, every time the car would idle I'd get freaked out because of how bad it felt. Any of you drive you car home knowing there was a problem but not sure what it was, and not sure if you'd make it? I was so frazzled when I got home I just went to sleep without eating.

I was worried I wouldn't be able to figure out what was wrong so I put it off looking at it for two days. Today I popped the hood, flashlight in hand. I looked everywhere and didn't see a damn thing wrong. Well, the first step in trouble shooting if you have aftermarket parts it take it back to stock. I figured the BOV would be the easiest first step, but everyone swears up and down about the hybrids being good to go. I reluctantly took it off and replaced it with the stock BPV. Cranked up it, but it was in cold idle so there was no telling if I fixed it. I hopped in and took it for a quick highway spin to get it warmed up. First thing I noticed are shifts are a lot more pleasant without the psssssshhhht sound, especially low pedal nice shifts where with aftermarket BOV would still make a noise no matter how nice you were driving. I got back to the city streets, fearful to come to a stop because I was sure the bov wouldn't have fixed the problem. Guess what...... it did...... The idle was a little harder than stock, but that's what I was expecting with mounts. I was so sure it couldn't be the BOV that I wasted the time to put the GFB back on... guess what.....the horrid idle returned. I pulled the GFB off, took it apart, and put it in my parts cleaner. I re-assembled it and put it back on. Can anyone guess??? Yep same freaking thing, I looked and made sure the piston was completely closing, but it was acting exactly like it should, so I yanked that biatch out and threw it in a box and put my stock back on. I took it for a pretty rough spin, pulled over, reset the ECU, then put the stg2 cali realtime map back in. Beat on it for a few more minutes, did a vishnu reset and beat on it for a few more minutes. The whole time noting much nicer and smoother shifts, no backfiring, zero idle searching when I was at a light, and no rough idle. go figure.

Moral of the story? It doesn't matter WHAT BOV you put on, you risking pissing on some part of your running. With stock tranny and motor mounts you might not notice it much because of how squishy things are, but it is screwing things up. Unless you have some sort of EMS that you can completely re-tune your curves account for the bypassed air, and the slight leak to the outside world at idle then DO NOT PUT AN AFTERMARKET BOV ON, it's not worth it. By all means if you want a worthless mod go for it, but after this experience I'm convinced no matter what the price it's not worth it.

 

well, i guess you mean for stage 2 peeps then cuz when you go stage 4, your gonna need an aftermarket bov.

 

Most people that go to that high of boost will have an EMS that they can reprogram the curves so you avoid the ****e idle and backfiring.

 

Lets make this simple.

Your engine figures out how much fuel to supply by reading a few things. One of those things is the voltage from the MAF (mass air flow) sensor. This sensor is on the plastic part of intake system and helps to calculate how much air is coming into the engine. Your BOV is forwards in the airflow from this sensor. This means that the air which already has been considered by the MAF, but has not yet reached the engine, is getting farted out your atmospheric blow off valve. So, the ECU thinks there is more air headed for the engine than there really is. Remember I said something about fuel supply? Well the ECU figures out how to best shoot the fuel injectors through some fancy calculations based partially upon what the MAF it. So, its injecting an amount of fuel based upon, like we said before, more air than is actually going into the engine. This means the air/fuel ratio (AFR) in the engine will be too low, or too "rich", that is: too much fuel. Engines act wonky when the AFR is rich, especially at low loads, low boost and low RPMs. It also makes for afterfires (not backfires, that's flames back into your intake system, not your exhaust... just think about the direction air is flownig). All that extra fuel in your exhaust system gets ignited on the next cycle after the blow off.

So you put in a 50/50? "So what?", I say. The mount of air you've removed is 50% less than that mistake you made with a 100% atmospheric BOV. You still have the same problem, just not as bad. You're still wasting gas and dirtying up your internals and you're not making your car any better than it was with the stock BOV.

No amount of ECU tuning will fix this. The only way I know of to fix this problem is to not use a MAF before the BOV. Can you switch their order? Not really.

The stock setup address this issue by returning the blown off air back into the intake system, after the MAF but before the turbo (and so before the BOV). This performs a sort of conservation of AFR while still letting the BOV do its job of relieving the turbo.


jason

 

^^^ should be a sticky, provided I'm right

 

Stock there's a "fudge" factor built in to account for the blowback when the BPV is venting. You can tune around the venting with a good EMS, or re-map. I was expecting the backfiring between shifts due to the rich condition I was creating blowing some of the air outside, what I wasn't counting on was the slight loss around the piston at idle. The stock BPV uses a pretty good sealing diaphram(similar to a valve and valve seat) that's only opened when the pressure in the intercooler is significanly lower than the manifold pressure, like when you let off the gas very abruptly for a shift or other reason. The GFB 50/50 BOV I was using uses a piston style seal which is a very **** poor seal. Even when idling when there should be no leaking what so ever, but I could hear a slight suction by sticking a tube by my ear then poking around right by the vent, so it was definately leaking. This very slight leak was enough to **** off the idle fudge factors. I'm willing to bet I was running slightly lean at idle because of the extra air sneaking in at the BOV. If you can re-tune the map, such as xcede or ecutek, it should be very easy to get around this, but I'm still an accessport weenie until january when I'm paying Mike a visit at gruppe and having an ecutek tune with my VF34 install.

 

Quick question - Im using a turbosmart plumback BOV , that shouldnt affect my AFR at all should it??

 

From looking at the model pictured on Turbosmart's website, it looks like it does exactly what the stock unit does - seems like it should be just fine. Honestly, its a waste of money though... unless you're running more boost than the stock BOV can deal with, you don't need to replace it.

jason

 

YA at 15.5 or so but plan to go higher ,looking into Xede so things will change . I just didnt want to run rich with an atmosphere plus I hear they run like sh** anyway

 

question: how would the ecu know how to increase/decrease fuel. when the MAP sensor is before the bov? evan with ecu tuning?

i could see how this would work if the ecu could some how sense the rich mixture after the bov.....

 

A fuel map is pretty easy, based on this MAF reading, give this much fuel, (well in it's simplest form). With something like ecutek, xede, or in the future access tuner, you raise or lower any of the fuel points depending on your needs. I haven't programmed a subby ECU personally, but I'm sure it's similar to the AEM EMS I was using with my turbo prelude(although personally I find the EMS is a MUCH more powerful ECU, aside from the learning capabilities).

 

i can see how a tuned MAP would work. raising lowering pionts etc.
but wouldnt you need something that is constantly changing/retuning the A/F MAP automatically. because of the bov venting at pretty much any moment.

meaning: the new MAP would be a constant pattern increasing fuel here decreasing fuel there.
i dont know about you, but i dont drive in a pattern. i let off the gas at any moment.
and without an extra sensor after the bov letting the ecu know when to change the fuel mixture, because i'm letting air out into the atmosphere and not into the engine. then how would changing the fuel MAP fix this problem? without an extra sensor of somekine?

thanks

-ROB

 

It's the same way the air is accounted for to begin with. The air vented back from the BPV is unmetered. They say at this % load, this much throttle, this MAF(Mass air flow) reading, this MAP(manifold air pressure) reading give me this much fuel, this much timing, and this much boost. They pre-condition the ECU to expect the air returning behind the MAF sensor. That's why adding an atmospheric BOV causes problems. Since the ECU is already expecting the air, the ECU dumps in fuel based on the sensor readings, which since there's less air it becomes rich. The same way an intake with odd MAF readings can be tuned for, a BOV not giving the same quantity of air back to the motor could be accounted for.

My EMS had a deceleration map also, which the subby might as well, which helped me tune so that at time the motor was decelerating is was the best it can be with no excess fuel, and ready to be stomped on again at any time.

Things like the xede modify the stock signals so to tune that properly you have to find out how much you need to lie to the stock ECU to keep it happy and make the most power

Edit looking at the Xede software, there are deceleration options as well as idle stability control, so you can tweak both of those to meet your needs.

 

i see...never heard of a deceleration map before.
so when you let off the throttle the ecu would just stop sending the extra fuel, that was previously sent by the intake MAF sensor.....correct?? allllright!

 

Couldn't it also be possible that due to the motor running rich, one of the cats coudl be clogged? I know a clogged cat can cause a ****ty idle, also. And if he's backfiring that badly, it's definitely a possibility, right?