2G BOV Recirc

[Slahm]

On a DSM with a MAF, while venting the BOV to atmosphere, I have read a number of post talking about running rich if I vent the BOV to atmosphere during shifts etc, but I thought the injectors will be in fuel cut when I release the throttle all the way at a full power shift.

How would the car run rich at a 0 percent TPS while shifting, other than at idle?

Thanks!

Peter

 

[Andrew_99_GST]

Sorry if I didnt understand the question correctly, but when you push the clutch in, your injectors fire.

 

[chrysler kid]

The turbo operates in a closed system, the air is drawn in through the mas where it is calibrated to be taken into the engine. When the bov lets air escape that initial gasp of air from the trottle body opening back up is suppose to be back in the intake being sent through the turbo, the computer thinks the air is already there, and when it is not the car adds too much fuel when it is not needed

 

[2gmitsueclipse]

This has been discussed 100's of times.
See this link:
http://www.dsmtuners.com/threads/venting-your-bov-to-the-atmosphere.113858/

 

[Meinleat]

The air has already been measured by the maf. When you release the air to the atmosphere when you shift your ecu will believe there is more air than there actually is in idle making for a rich or hard idle.

 

[Meinleat]

The only way you can run a non recirculating is with speed density conversion and a gm maf I believe.

 

[chrysler kid]

I think the better question is why would anyone want to vent the blow off valve. To be technical it is merely a boost pressure regulator, and the term blow off valve only came around because of the sound the aftermarket units would make


Hell the absolute best way to make the blow off valve louder would be to get an aluminum recirc tube and an aluminum intake. My greddy type S is louder and echoes inside of those aluminum intakes.

 

[pauleyman]

Bov does not regulate boost. A popoff valve will. Its purpose is to release pressure upstreamm of the turbo.

 

[Slahm]

I guess I was not clear, sorry, my question is why the car would run rich in a situation when from what I can tell, it should be in fuel cut... You are NOT accelerating, the engine is typically revving quite high, and one can only assume the TPS would be at zero for many people while shifting, so how exactly will it run rich? On a DSM, if your TPS is zero, or your idle switch is engaged, the car will fuel cut if very far above idle, correct? The engine should be DEccelerating, rather than accelerating, so it will not be injecting much(if any) fuel. So how does this result in a rich condition?

I DO understand why this would be if you could be blowing off AND accelerating(say a leaky BOV), as the Air measured by the MAF would certainly be wrong, and it would introduce too much fuel, but I don't understand how this could happen in a decel condition. That is my question.

Also, I am not trying to discuss whether venting to atmosphere is a good idea, I just don't understand how it would run rich in this case. This is more about me understanding the ECU than whether it is a good idea. Many others address this.

 

[Cox Abele]

I understand your question.

Your car does not always cut fuel injection when not on the throttle. If it did, the car would not idle. 0% TPS does not equal cutting injector pulse completely. Yes, there are instances where the injector pulse will be cut, but there are a equal number of situations where the BOV will open and the throttle is not 0%.

Go WOT, then back off to 50% throttle. Your BOV will open, but your injectors don't stop firing.

At idle, there is usually enough vacuum that the diaphragm pulls the valve open. This is where the fabled "vented and rich" comes from. Once on the throttle, vacuum decreases and the valve will seat until there is either enough vacuum to pull it back open, or enough vacuum on the top of the diaphragm and positive pressure on the valve face to open.

You are correct in understanding that going from WOT to snapping the throttle shut completely will generally not result in a rich condition because of the injectors being cut. This is about the only time you wouldn't be running rich with the throttle closed. This is only for the time that the engine does not need any additional fuel, however to keep from stalling, it will eventually (very quickly) begin to inject fuel in order to allow the engine to idle at which point the vented valve has released metered air. The venting of unmetered air will result in a rich condition.

 

[Slahm]

Your first example seems to be make sense, although I would argue that a properly adjusted BOV would not do this, but maybe it would, I have not really thought it through or tested it. When mine did that, I adjusted it to not open unless it developed a fair bit of pressure, but I could have it adjusted badly.

Your second example at idle(fabled "vented and rich") would not unless I misunderstand, in fact, it SHOULD result in a lean condition as it would be PULLING air in the BOV if at vacuum and leaking. It should not be pushing out the BOV if the car is in a vacuum condition. I suppose this could be wrong if it is in vacuum on the far side of the throttle body, and boost on the near side, but that seems like letting off quickly, as in the third example.

If I understand a normal BOV, it opens when there is MORE vacuum on one side of the diaphragm than on the other, not just under vacuum.

Thanks for the info, if anyone has any further thoughts I would love to hear them.

Peter

 

[Cox Abele]

Don't try to re-invent the wheel. It's recirculated from the factory for a reason.

 

[Slahm]

It's limited to mid to low hundreds of AWHP from the factory, it's set to a very low boost setting from the factory, so leave your car there, right? Maybe only use the factory injectors, and turbo right? Factory exhaust? No point upgrading the suspension, they put it on at the factory.

Maybe don't be intentionally unhelpful.

If you had read what I was saying, you would have understood that I am trying to LEARN about things, in this case, the ECU and how it reacts to the TPS, including how that affects the AFR, and whether the SPECULATION on here and elsewhere is accurate or not. I have given a couple of points that show the conventional thinking at least IN PART is wrong about the richness of the AFR because of the BOV,(at idle, as above) and was looking for more information, as I don't take everything I read on the internet on faith, particularly when I find otherwise, as I do in this case. Why be an ass rather than just saying you don't have anything to add?

Why does the world insist on saying search when they are to ignorant or lazy to add something useful, why have a forum except to discuss your thoughts on things? Google is for searching, forums are for asking or discussing, if you don't want to, at least stop telling people to search, maybe they are bad at searching as well as fixing cars! Why on earth tell me with NO explanation as to why, not to change something simply because it came that way when I bought it? Damn.

Oh, and thanks to those who actually read the question and gave thoughtful advice. I do appreciate it, as I already said.

I suppose one more question relevant to this would be to confirm that a properly operating BOV is ONLY open when the vacuum at the source(typically the intake manifold) is greater than the other side of the diaphragm(typically the upper portion of the BOV), is this correct? I am not wondering about situations where a BOV is opening incorrectly.

 

[chrysler kid]

Your first example seems to be make sense, although I would argue that a properly adjusted BOV would not do this, but maybe it would, I have not really thought it through or tested it. When mine did that, I adjusted it to not open unless it developed a fair bit of pressure, but I could have it adjusted badly.

Your second example at idle(fabled "vented and rich") would not unless I misunderstand, in fact, it SHOULD result in a lean condition as it would be PULLING air in the BOV if at vacuum and leaking. It should not be pushing out the BOV if the car is in a vacuum condition. I suppose this could be wrong if it is in vacuum on the far side of the throttle body, and boost on the near side, but that seems like letting off quickly, as in the third example.

If I understand a normal BOV, it opens when there is MORE vacuum on one side of the diaphragm than on the other, not just under vacuum.

Thanks for the info, if anyone has any further thoughts I would love to hear them.

Peter

It seems like you are questioning the difference between engine vacuum and boost and how a blow off valve works.



https://www.google.com/search?site=...bile-gws-hp..0.16.1114.3.tkBkU0llVbw#imgdii=_

 

[chrysler kid]

I didn't mean to be condescending with the Google link.

If you are just wondering why a vented bov would cause the car to run rich after release, it doesnt. It runs rich after the tb opens back up and the released air isn't coming back up the intake to stabilize the pressure. So the intercooler pipe is back at atmosphere pressure while the mass air flow sensor is picking up suction from the turbo.



So if you vent the bov and go back to idle, no problem, if you do an operation like shifting, there is a point where the intercooler piping would no longer be under vacuum and the mass air flow sensor is telling the ecu that there is vacuum being sent to the engine, but there is not. The engine opens back up expecting to immediately be responded with air, instead it gets a hiccup and can't breathe for a second. The air bubble doesn't get sucked in because it acts like a hole in the system. The vacuum of the air has to catch up to the pocket of air to be sucked back into the engine. If the turbo is recirculated that air goes directly back into the turbo and the vacuum to the engine and the tb was never lost

It's hard to explain. Poke a pin hole in a straw and put your finger over it as you take a sip of coke, when the straw is full and your drinking release your finger. The coke drink above the pin hole does not go into the engine and below the pin hole falls back into the cup, when you put your finger over the hole again, in order to suck the coke above the pin hole back in again the straw has to be filled with coke.

 

[Slahm]

I took no offense with the google link, I thought it was a nice touch!

I hear what you are saying and I am trying to understand what you mean, do you mean that when you get BACK on the throttle, AND the BOV is still open, it reads extra air, which I would understand would affect the AFR. Should the BOV not close as soon as the throttle is opened? Is this BOV lag what creates the problem? The reason I have never assumed that this was the case is that any time I have vented to atmosphere, I have had no performance issue at the point of opening the throttle, but I could understand this being a problem. Is this moment an actual problem to people? I would have thought performance wise a bit of extra fuel at this point would be good unless we are talking car stalling richness, although not for emissions, I suppose.

By that, I mean is there an actual performance problem for a second, or is this a theoretical richness thing to avoid? Could this not be addressed by a tighter BOV?

Not beating a dead horse here, just trying to wrap my head around what the actual issue is, and how relevant it is to an actual driver. So far, having done it both ways a few times, I have noticed none of the symptoms, and had assumed that at idle, people that were non recirculating and having problems had a leaky BOV, rather than a properly working one. I still don't really see any other explanation(at idle), but could just be stubbornly not understanding.

I had sort of assumed this was the chief complaint from my searching, although confirmation bias may have come into it I suppose.

From what I am reading now, here, and other threads, I am assuming the biggest concern other than that is a hesitation when getting back on the throttle. Having not experienced this, I have very little input.

Thanks again!

Peter

 

[chrysler kid]

Engine vacuum and atmospheric air are different.

Vacuum is the force of air being sucked into the engine, the engine is asking for air and in a close system it immediately receives the air it asks for.

Atmospheric air is not being directed to the engine, and only exerts force of well nothing. This bubble where air is released and is now not directed towards the tb means the suction from vacuum has to travel back from the mas air flow sensor to re establish the vacuum or suction

Boost is air being forced into the engine. Boost gauges make it complicated but vacuum and boost are both forces of air going into the engine.

In order for the mas air flow sensor to correctly calibrate the fuel, the engine must always receive the amount of air that is taken past the sensor.

 

[chrysler kid]

I'll go a step further, beyond losing boost when the blow off valve opens you lose vacuum.

That area from the turbo to the blow off valve now has no usable air, it is void of any usable substance for the engine to use to combust. The engine wants that air immediately, but as soon as the tb opens and the vacuum from the engine says bov close, there is immediate suction. That bubble of 0 pressure can't be sent to the engine. It is still air, but there is no pressure or movement that can be applied to it until the actual suction catches back up from the air taken in. (Think about my coke drink example, you have to bring back that suction to bring the drink back in)

At idle after blow off of vacuum and boost there is no immediate response of rich or lean, with the tb closed the engine isn't requesting much air out of the intake so you may see idle dip slightly if at all

Basically you displace the usable air in the intercooler piping that is before the bov. Now you have a gap where there is no boost, there is no engine vacuum. If you are sitting in the intercooler you are sitting in the eye of the storm where there is no wind and no suction.

The engine thinks that the constant loop is still in tact and sends the fuel for the correct engine vacuum, but now you have a section of piping in your car that is missing the air the computer expects to be there.

In a recirculated system this action is minimized by that pressure being immediately shot back into the turbo in case it is needed right away.