So I'm going through my car to just make sure everything is ready for summer and I did a routine boost pressure test. Everything is tight except the little box starts making noise at about 6psi. I noticed this last summer when I pressure tested my system but can anyone tell me if this is normal and what that box is? I also put on my XO2 exhaust and included a video of that too. For $450 this exhaust looks pretty nice (except for the tips, but they are ok for now). The install took less than 20 min once I removed the old exhaust. Oh and a tip for removing the stock exhaust is to remove the subframe brace so you can just drop the whole thing down in one piece rather than trying to grind off bolts or cut your exhaust in two.

First video is the boost pressure test:

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Second video exhaust start up and low reving:

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bump

 

Come on someone has to know what this box thing is?

 

Someone has to know what this is.

 

I don't no what it is, but when I did a pressure test it started make noise around 9 psi.

 

Looks like it has coolant into it and out to the throttle body (warm the TB up) and elsewhere..Maybe a small circ motor within it..Don't know what its called however..

 

^^ Yeah that would explain the gurgling sound if it has coolant in it. Guess it sounds like this is normal though. If anyone else has any input I would really appreciate it.

 

It's the purge solenoid for the EVAP canister.

Pressure is forcing it to leak a bit. A one way check valve of some sort may be a good idea on the manifold side of this solenoid to prevent the leak. I now wonder if mine does the same thing.

 

So are we all losing horsepower?

 

A simple answer is probably not enough to make doing anything about it worthwile.

It's doubtful that there is a big enough leak to really cause an issue. I just feel it is generally a good idea to make the system as boost leak free as possible. Also by looking at the system diagrams, it *may* be possible that a leak such as this could pressurize and damage the carbon canister or the fuel tank itself. Since there are many many cars running around FI and nothing I described has happened to this point, I'd say that it's very unlikely.

Technically, if you're running a MAS system, it is metered air that is not making it into the engine and could cause tuning inconsistancies. As I said before, it shouldn't cause an issue in the amount I can see flowing through that solenoid, unless it is getting blown completely open at some point. Something to keep in mind is any extra amount of work the compressor has to accomplish to provide the airflow at pressure causes the turbine to work harder and leads to efficiency losses in the turbocharger system.

It's often overlooked how cold side restriction or leakage effects turbine inlet pressure and volumetric efficiency overall.

 

Everything you say makes sense and I also have to assume that every 350Z out there with FI has the same leak. I have never heard of anyone talking about it so I guess we can just consider this part of the "way the car is". I think there may be risks in tampering with this solenoid as that's the way it came from the factory. I don't understand what it's purpose is so for now I'm just going to leave it alone. But hey if it is discovered that this a source of boost leak that can be fixed with a one way valve or something then we all might have a new trick to squeeze out a few more hp from our cars.

 

I do remember when I did mine, I pinched the line coming from the throttle body with my fingers, and the sound would change. I'd say there probably is a check valve in there.

 

The purpose I believe is to regulate/evacuate fuel vapors from the gas tank. An electric solenoid is not suppose leak. Either it is purging vapors or it isn't. Hmmm....

 

Correct, the solenoid is operated when certain conditions are met to purge the fuel vapors from the carbon canister. The solenoid is designed to have a vacuum applied to it, not pressure, hence the leak.

A check valve in the hose between the intake manifold with flow direction going towards the manifold would easily solve the problem, if a problem really exists.

 

Whatever it is designed for, the solenoid is either open or closed. I don't see how boost vs. vacuum would make a difference UNLESS the solenoid is open when it shouldn't be. That would indicate an electrical fault. Not saying I know for sure, but the underlying problem may not be obvious...

 

So if vacuum is all the canister needs then would putting a one way valve solve the problem as its been suggested?

 

I think that would fix it, but the question is whether this is a true fix or not. If you think about it for a second, what happens when the EVAP solenoid tries to vent but you are in boost. The one way valve will prevent boost from entering the rear canister, but the vapors still cannot vent. This might happen as fuel temps increase, for example. The EVAP system really needs a constant vacuum source all the time. I suppose with FI, if you want to be safe (but eco-unfriendly and illegal) vent to atmosphere through a catch can.

I need to read the FSM and do some research... I know for a fact some folks get rid of the EVAP system all together. I presume they vent to atmosphere but I would love to hear from someone with firsthand knowledge.

 

The way these solenoid valves work, they can be forced open or operate improperly if outside the designed operating range, this includes temperature, pressure, direction of flow and fluid. Think of fuel injectors, they are designed to operate below a specific duty cycle and fuel pressure. Get above that and the injectors can go static, leak, or not open at all.

This specific valve is intended to seal a higher pressure (atmospheric pressure or slightly above) from a lower pressure (intake manifold). With that type of pressure and direction applied, the valve is designed to use the pressure differential to help force the plunger against the seat and seal the valve. Working backwards with more pressure than the valve is designed to see is overcoming the spring pressure and forcing the plunger off the seat at a positive intake manifold pressure, causing the plunger to vibrate, that's the noise experienced.

I've been boosted for 12K miles now and have never had any EVAP codes, I'd almost be willing to bet that at the BSF that purge is operated is below BSF when in boost, that's why the ECU doesn't freak out. The FSM doesn't give me any specifics on when it operates, it does however explain that the canister vent valve is normally open and only closed to check for a pressure drop when the system does it's leak checks.

Removing the system as a whole would most likely result in a handful of codes and a lighter, less cluttered vehicle. I have not accomplished this myself.

 

BTW: It is the EVAP canister purge volume control solenoid valve specifically.

 

Damm Bro, your new exhaust sounds good with vortackkk!

chefj