Can anyone tell me what the pictured hose and device does?

 

 

 

 

 

 

I've been trying to find thecause of a cylinder 2 misfire.  I decided to start with a basic tune up since it was due, which included air filter, spark plugs, ignition wires, and PCV valve.   Thats when i noticed the hose was disconnected.  I'm not sure if it was off before i started, or if it might be the cause of the probelms.  thanks

 

*Edit* added better photos

Edited March 8, 201511 yr by sario

Not sure. but i drove around with out it on my brat for a few months and never had a problem. what all have you checked as far as the misfire?

Are you talking about the thing with the green line on it? Canyou zoom out a bit, for some reason I am disoriented with this pic.

It is the hose with a green strip.   It drives some people nuts, but I paint pen everything when i pull an engine.  I updated my post with what i hope are better photos.  Also, I don't think I mentioned this a 97 outback w/ auto.

 

The misfire is intermittent.  I've only had the light come on when it's cold outside, around 32, and I when i drive up a hill shortly after starting it.  But I have noticed my fuel economy was down to about 19.5MPG which is about 3 MPG lower than normal for my current work commute.

Edited March 8, 201511 yr by sario

Much better pic.

Edited March 8, 201511 yr by nipper

http://ww2.justanswer.com/uploads/baddad1/2011-04-16_163643_capture.png

http://ww2.justanswer.com/uploads/baddad1/2011-04-16_163643_capture.png

Thanks nipper.  From that picture i think its the "pressure sources switching solenoid valve."  Now i have a name, I have so googling to do.

The PSSSV switches the pressure source for the MAP sensor. It changes between atmospheric pressure and engine vacuum so the ECU can tell what elevation you're at. Not a super high priority sensor, the ECU only makes fine adjustments to fuel mixture based on MAP input. On your car it really only uses it for determining elevation.

 

That hose being loose will cause a small vacuum leak which can cause a lean condition at idle.

 

Misfire is likely spark plugs or old plug wires.

Front O2 sensor could cause this as well.

The PSSSV switches the pressure source for the MAP sensor. It changes between atmospheric pressure and engine vacuum so the ECU can tell what elevation you're at. Not a super high priority sensor, the ECU only makes fine adjustments to fuel mixture based on MAP input. On your car it really only uses it for determining elevation.

 

That hose being loose will cause a small vacuum leak which can cause a lean condition at idle.

 

Misfire is likely spark plugs or old plug wires.

Front O2 sensor could cause this as well.

Do you think the vacuum leak could explain losing 3mpg?

The check engine light seems to come soon after starting when cold.i think it's still in open loop at that time, and probably not the 02 sensor.  Anyway its supposed to get to 30 again tonight, I'll see what happens in the morning.

 

The PSSSV switches the pressure source for the MAP sensor

 

The OP car has a MAF.  Why would the MAF, which is really does measure mass air flow, need the pressure reading?

Don't know for sure but Subaru paired up on MAP and MAF sensors for several years. On MAF based fuel systems the primary air density calculation is done by the MAF and the MAP is only used for secondary checks.

 

Generally if the car has EGR it will also have a MAP sensor because the MAP signal is used to determine if the EGR valve is opening by measuring the pressure change in the intake manifold. This is paired with inputs from the O2 sensor to determine EGR flow.

 

Some also use the MAP sensor to check purge flow of the evap system.

And as said before, the MAP is used to determine elevation. Higher elevations need less fuel to maintain stoichiometric ratio because the air is less dense. The ECU checks this as soon as the key is turned On, and also periodically while the engine is running.