Evap Emissions fault

4

4orester

The OBD in my 04 Forester tells me I have a small leak in the fuel evap
system. Any Idea what could be causing this? I've erased the fault 3 times
now, but it comes back after about 80 km or so.

I don't see any fuel on the driveway or smell any fumes. Gas cap is
original, clean and tight.

Has anyone had a similar expereince?

Thanks for your help.
 
The OBD in my 04 Forester tells me I have a small leak in the fuel evap
system.  Any Idea what could be causing this?  I've erased the fault 3 times
now, but it comes back after about 80 km or so.

I don't see any fuel on the driveway or smell any fumes.  Gas cap is
original, clean and tight.

Has anyone had a similar expereince?

Thanks for your help.


Any work or wrecks before the problem came up?

These can be hard to find so, anyplace where some maintenance or
repair has been done would be a good place to inspect. The evap vacuum
and vaporlines go all over the place. Sometimes a 'smoke test' will
show a leak in a vacuum line.
 
The OBD in my 04 Forester tells me I have a small leak in the fuel evap
system. Any Idea what could be causing this? I've erased the fault 3 times
now, but it comes back after about 80 km or so.

I don't see any fuel on the driveway or smell any fumes. Gas cap is
original, clean and tight.

Has anyone had a similar expereince?

Thanks for your help.


Any work or wrecks before the problem came up?

These can be hard to find so, anyplace where some maintenance or
repair has been done would be a good place to inspect. The evap vacuum
and vaporlines go all over the place. Sometimes a 'smoke test' will
show a leak in a vacuum line.

===========================

No work was done other than the regular oil changes. I should have added
that this problem (as expected) got progressively worse with time, with the
intervals between fault resets getting shorter and shorter - much as I would
suspect with a decaying gasket, hose or loosening connection, but nothing is
obvious so far.

Does any fault registered with the OBD cause the system to go to a default
mixture? My mileage sucks when the light is on.
 
Any work or wrecks before the problem came up?

These can be hard to find so, anyplace where some maintenance or
repair has been done would be a good place to inspect. The evap vacuum
and vaporlines go all over the place. Sometimes a 'smoke test' will
show a leak in a vacuum line.

===========================

No work was done other than the regular oil changes.  I should have added
that this problem (as expected) got progressively worse with time, with the
intervals between fault resets getting shorter and shorter - much as I would
suspect with a decaying gasket, hose or loosening connection, but nothingis
obvious so far.

Does any fault registered with the OBD cause the system to go to a default
mixture?  My mileage sucks when the light is on.

There IS a 'limp home' mode. Not sure exactly what/how many conditions
would trigger that - likely the CEL would be flashing though.

I THINK 04s still have the Engine Temp Sensor (not Temp gauge sender -
which would be separate). If it's bad, your car can stay in 'choke'
mode all the time, run rich, and won't throw a code.

Definitely have a look around and ubder the intake system for loose
hoses. Not impossible for a gas cap to go bad I suppose.

Perhaps getting the frezeframe data and looking at the fuel trims
might help a little.

If you search/post around http://www.subaruforester.org/
ultimatesubaru.org and scoobymods and NASIOC etc., you might run
across the 'most common' evap/vacuum problem areas. Be prepared to
tell them the miles,condition of your car and the exact trouble code
you get.
 
Do remember that this fault can be posted for just a loose gas cap. So check
the cap and also the top of the tank-filling pipe where it attaches: Just a
bit of really tough dirt, that did not get wiped off when you put the cap
on, could cause enough of a leak to trigger this. Maybe not too likely, but
certainly an easy check, and fix if it pays off!
Bob Wilson
 
The fuel evap system has little to do with the engine itself, but has to
do with the ECU. In fact, the only relation between the two is the line
running from the carbon canister to the purge control solenoid valve
that connects the canister to the manifold vacuum.

I have uploaded the Evap system description for the 03 Outback here.
Hope it helps you understand how the system works.
http://dl.dropbox.com/u/33330380/8_Evaporative.pdf

I have uploaded the H4 diagnostics for the 03 Outback (I know, not an 04
Forester). I can imagine that this may be of some help in pinpointing
the problem. Refer to section 19, PFD page 121 for the small leak
diagnosis.

The file can be found here:
http://dl.dropbox.com/u/33330380/2003 Outback Diagnostics H4.zip

I always find Evap system troubles to be a pain.

Good luck,

AS
 

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