Evap system help - P0440 - carbon in purge line?

[jaketrimble]

Hi!  I'm new to the forum, registering after having lurked a fair bit.  I have done a bunch of searching but decided to create a new thread because I didn't want to revive an old one and didn't see anything quite like what I'm encountering.  

 

My car is a 1997 Legacy with 170,000 mile or so.  I've had this P0440 code for a year or so and at one point had a shop do a smoke test and they verified there were no leaks.  They said the vent solenoid was functioning intermittently and that they could replace it, but for the moment it was working.  I didn't have them replace it, passed inspection then promptly got the CEL again and the same code.

I read that the code could mean the system is unable to achieve a vacuum, so I pulled the charcoal canister to weigh it.  I heard on a youtube video anything over 2.5lbs means that the tank was likely overfilled and gasoline leaked into the canister, which could throw the code.  The thing weighs 3.5 lbs. and is currently sitting in the sun to evaporate.  I also notice the activated carbon is leaking freely from the purge hole on the canister.  Is this normal?  AND, when I pointed the dangling purge hose toward the ground, a bunch of activated carbon fell out!

 

I then connected the green diagnostic cables below the dash and checked out the solenoids.  The vent valve by the canister appears to be fine (it clicks, although I didn't pull it off to check if I can blow through it), but the purge valve (behind the intake manifold) wasn't clicking, so I pulled it off and applied a charge and verified that it doesn't close at all.  It reads around 25 ohms, but if it doesn't close, that doesn't matter, right?  When I blow through the vent hose that was connected to the purge solenoid (that I think connects to the canister), it is totally blocked-- no airflow.  Should I be able to blow through the hose to where the canister was? I don't have a compressor so I was just blowing with my lungs. 

 

Excuse my ignorance, I'm new to cars (mostly worked on bicycles) and I'm trying to understand how this all works.  It seems to me the carbon should stay in the canister, so if its leaking maybe the canister's broken?  Can it be rebuilt or cleaned?  And if the purge valve doesn't close, that needs replacing too, right?  What about the hose?  Should it even be open with the purge valve and canister removed, or is there anything that would block it in between?  Let me know if I can provide more info / clarification.  Thanks for your help!

[Fairtax4me]

Yeah you need a new canister. At some point it has been saturated with liquid gas and that causes the structure of the carbon to fall apart over a period of time.

 

Likely some carbon chunks have been sucked into the purge line and it is clogged. Leave it disconnected from the canister and try blowing it out with compressed air. If you can't get any air to go through it at all, first try removing the rubber sections at each end and see if you can blow air through the steel line. If air flows without the rubber sections in place, just replace those sections. If you can't get air to move through the steel line, you may need to replace the steel line. Some coated steel brake line should work fine for that.

Don't put that canister back in the car. You'll never get all the peices of carbon out. They'll just get sucked into the line and clog it again.

 

 

The purge solenoid can be taken apart by bending the little tabs together. Pop the end plate off and the valve pretty much falls part. Blow the chunks out with compressed air and reassemble.

 

Hoses. From the purge valve to the engine, you should block that off because it will cause a vacuum leak and can cause a rough idle.

The hose from the canister to the tank you can just leave open for the short term.

[jaketrimble]

AHHH theres' charcoal everywhere!  Thanks for your reply Fairtax4me, it was very helpful.  Here's the update: I was able to open and fix the purge solenoid just as you described.  Bits of carbon fell out of it but now it seals shut and functions perfectly.  Today I was able to go up to a neighbor's place who had an air compressor.  Strange phenomena when we blasted air through the line-- there was a tiny amount of flow on the other end by the canister, but then when we would remove the nozzle of the compressor, bits of charcoal would spurt out of the same end where we were blowing through.  Seemed counter intuitive, I'd love if anyone knows the physics behind this.  It happened repeatedly but we were able to unclog the line in bursts with this method.  We had to pull off some of the hoses under the hood and clean them out individually but eventually we were able to get proper flow through the whole line and I am quite confident it's clear now.  So with the 25$ charcoal canister from the pick n' pull I'm all fixed now!  If I don't respond again that was the only issue, otherwise I'll post when the CEL comes on again.  Thanks again for the advice/help!

[Fairtax4me]

You put 30-40-100 psi into a line that's clogged its gotta go somewhere when you take the nozzle away!

 

Glad to hear you got it cleared out!

[psychocandy]

Holy thread resurrection.

 

I replaced the little tiny filter on top of the engine. I removed by charcoal canister. It weighed 4.5 lbs! 

 

I'll either go to the pick'n'pull & look for one, or try to find one online. Then report back if it clears the code. 

 

How do you inspect the filler neck? I looked down it with a flashlight. i don't think I saw anything. Previous posts imply that it's obvious if the filler neck is rusted out, but I'm still not sure what I'm looking for. After all, there's that little flap that makes it hard to look down the gas-hole. And can someone link to instructions on how to test the valves from under the the dash? Perhaps with pics?

[Fairtax4me]

Jack up the right rear corner of the car, take the wheel off, remove the couple of 10mm bolts that hold the stupid plastic cover on the fill tube and yank the cover off. Now if its rusted out you'll see where its rusty. Usually at the bottom of the bend.

[psychocandy]

Trying not to start any new threads since this is a common issue. I feel like I'm just throwing parts at this CEL (but they've been cheap parts, so not too concerned). Still, I'd like to get rid of it.

 

Don't remember any work done on the car or changes made to it before the CEL came on. with the P0440 code. It's a high mileage car with ~170k on the engine.

 

I have checked the fuel filler neck. There was a bunch of dirt/crud under the plastic cover, but no visible rust. Compared to some pics/vids I saw on the internet, it looked to be in VERY good shape (CA car, so it stays in a pretty dry environment, no salted roads, etc.). I also checked all the hoses attached to the neck. Again, dirty/dusty on the outside. But still nice & flexible, not brittle at all. Also, the gas cap rubber seal looks brand new and the top of the filler neck is also very clean.

 

I did replace the charcoal canister. I removed & weighed it and I think it was over 4 lbs. The replacement came from the pick-n-pull, so no real guarantee that the one I replaced it with wasn't past its prime either.

 

I have not checked the fuel shut of valve attached to the side of the fuel filler neck. If this valve was bad, would it throw a P0440? How do I test this?

 

Also, reading this thread again, I think I should also check the solenoids for the vent valves. I understand that there are some green wires under the dash, but can't seem to find a tutorial/step-by-step for this. I have a 97/98 Impreza Outback with the charcoal canister at the rear of the car. Can anyone point me to some either a step-by-step guide w/pics or maybe even a YouTube vid about how to check these?

 

Much appreciated, thanks in advance!

Edited August 14, 2016 by psychocandy

[mikec03]

You should be able to find the two green wires under the drivers instrument panel.  You have to work upside down of course.  When you plug them together, all the car solenoids and rad fans will click on and off in sequence.  It's a 90% chance in my opinion, that the solenoid that is on top of the charcoal canister needs replacement.   You should have grabbed it when you got the canister.

[Fairtax4me]

The connectors are bright green. The wires are black and blue or something like that. But you'll see the green connectors easy enough if you poke your head under the dash. Usually to the right of the steering column with a handful of other connectors that have nothing plugged into them. 

 

Plug them in, turn the key to ON, and the solenoids and fans start clicking on and off. 

The canister purge solenoid is under the #3 intake runner and kinda tricky to get to, but the vacuum hose to it should be easy enough to get to where it goes on the manifold. Pull it off there and try to blow through the solenoid.