Evap Emissions fault

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.

Reply to
4orester
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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.

Reply to
1 Lucky Texan

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.

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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.

Reply to
4orester

snipped-for-privacy@x7g2000yqb.googlegroups.com...

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

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and scoobymods and NASIOC etc., you might runacross the 'most common' evap/vacuum problem areas. Be prepared totell them the miles,condition of your car and the exact trouble codeyou get.

Reply to
1 Lucky Texan

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.

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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:

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I always find Evap system troubles to be a pain.

Good luck,

AS

4orester wrote:

Reply to
AS

WOW. Excellent info. Thank you Tin_man!

I should be able to follow this to the problem. I think I may have caused it myself by continually overfilling the tank to squeeze out those few extra miles between fill-ups. Maybe I have saturated the carbon cannister or flooded some of the lines making the valves inoperable/damaged. I'll report on what I find.

....and thanks to all who replied.

Reply to
4orester

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