Just a general question but what should be the effects of a disconnected BCS?

I'm going over my EVO II engine bay today and I have found those hoses disconnected from the previous owner.

WADAD

 

BTW would that qualify as a boost "LEAK"?

I'm going to hook it back up but just wondering if there is any long term damage that could be caused by this?

WADAD

 

depends on if you have an mbc you don't know about. if you do then you should be running whatever boost level was there before. he might have just left it capped so you don't throw any codes.

if it's just really unplugged and what you're saying is you're running no boost control. well... you'd be really slow, running pretty rich (throwing a code there).

do some searches and just figure out how the whole system works. there's diagrams available too.

 

Thanks for the reply. I was told the car is stock except for the kn filter and muffler he put on.

The Speed limiter has also been removed. That is all.

I'll check to hook it back up tomorrow but according to the boost gauge I am hitting a peak boost of around 13.5 to 14 PSI. Stock they run around 10-12. The hoses are just hanging there with the clips still on them so to me it looks like someone forgot to hook them back up.

WADAD

 

that means you're running on watsegate pressure and either your wastegate is strong or your boost gauge is weak. hook those lines up but be careful... he had a flash which is why the "speed limiter" was removed. you might want to get this seriously checked out.

 

I'm going to leave well enough alone then...

As I look around the engine bay I see things disconnected. Until I get a better knowledge of the car itself I'm going to just forget about tampering.

WADAD

 

One last question though...

Is it possible that a flash can bypass the use of the BCS. I called the mechanic who usually works on the car and he said that I'd be running wastegate boost if the BCS is unhooked and that I should be ok.

Any more guru opinions on that?

WADAD

 

Does anyone know if you can bypass the BCS with a flash or not?

WADAD

 

Once you understand the boost control system, you should be able to answer this for yourself fairly easily

It's a very simple mechanical feedback system. The amount of boost that your turbo is currently making is sourced off of some reference line, typically tapped from the compressor outlet or intake manifold. This pressure is fed through a rubber hose back to the wastegate. The wastegate has a spring with certain known fixed spring rate (like 14 lbs for example). When the pressure in the line going to the wastegate exceeds the spring rate, the wastegate opens allowing exhaust gases to bypass your turbine and therefore stopping it from spinning faster and creating more boost.

The boost control solenoid is introduced into this system in order to control the amount of air pressure reaching the wastegate. It is able to bypass air that would otherwise go to the wastegate and therefore allow you to run higher boost than the wastegate spring tension. The BCS does it's bidding under the control of the ECU ... this is how the ECU can 'control' boost ... it sends a signal to the BCS to tell it to bypass more or less air in order to reach the appropriate boost target.

So if you understand the above, you should be able to answer the question at hand.

No, a flash cannot 'bypass' the BCS. A flash can modify the boost targets and duty cycle of the BCS stored in the ECU, but if the BCS isn't connected, the ECU has no way of controlling boost whatsoever.

With the BCS disconnected, you are reduced to the simple mechanical feedback system of your exact boost being fed back into the wastegate ... meaning you'll run exactly as much boost as the wastegate spring tension ... also referred to as 'running wastegate boost.'

The only way to 'bypass' the BCS is with some other form of 'airflow into the wastegate' control like an MBC, or EBC that effectively does the same thing as the BCS (bleeds away air from the line going to the wastegate) but is controlled by something other than the ECU (like twisting a knob for an MBC, or external computer control for EBC).

Hope that helps.

 

Excellent explanation...

It doesn't get much clearer than that.

Thanks

WADAD

 

i actually thot that was a great question for another reason. if you're running an mbc... there's no way to do a bcs delete is there... but i don't know if anyone has tried.

 

I just want to get this on the net so I can have my buddy look at it who used to own the car as well but there is no MBC on this car and here are the pics of the disconnected items.

Hoses


BCS hoses 2


BCS itself


Firewall thing



Firewall items disconnected.


The BCS hoses are not plugged and there is no MBC.

If the car is running rich that would explain the bad gasmileage I am getting but there is still power. Up in 4th though the car is sluggish as hell and I want to do a 2.5 or 3 inch exhaust but I want to make sure that it will not throw the car closer to whatever edge it might be on.

WADAD

 

can we get a few pics of the car itself?? =D

 

So is there nothing at all connected to the wastegate nipple? It looks like you're running with the wastegate line disconnected, in which case you will run the max boost possible that the wastegate flapper will hold before just blowing open due to the pressure. This can be unsafe due to the potential for overspinning the turbo, but then again if you're only hitting max 14psi it's probably not all that bad.

I don't know anything about the turbo in the Evo II, so I can't say what the max safe boost is ...

The supra guys used to do this as a super easy mod ... pull the wastegate hose for ~30whp or so .

The good news is that it seems like you have a very soft spring in the wastegate so you're not overboosting terribly. If I was in your situation, I would hook up an MBC pretty quickly to have control over the boost ... the lines are already cleared for you! Also, how sure are you of the accuracy of your boost gauge? You might want to check it against a 'known-to-be-accurate' MAP sensor ...

 

I just installed a mbc & if my calculations are correct I'm running at 24psi. I didn't think this was a problem b/c before the install I was running at about 19-20psi (which I've been told is stock.) If he is running at 14psi, is that really low or is mine way too high?