ok so short story is i've been having an EVAP problem that causes random misfires, usually after i fill up. the problem is that it seems to be purging the evap even at idle which causes a misfire. my understanding is that this is supposed to happen only at higher speeds when it doesn't matter so much to the engine.



valve is fine, i have pressure tested it. i DID however find the trouble....the damn ECU is holding it open at idle...had it sitting at idle, removed the connector and guess what? constant voltage.



so my question is simple: what should i start looking at and how should i handle this problem? i don't see bad wiring as this would cause a short to the ECU. however, the ECU itself could be the issue. what other electronics are involved? how does the ECU know when to purge the EVAP? is there a pressure sensor somewhere? very possible that it could be jammed....simple test would be to disconnect it.



any ideas? thanks.

 

from what i remember there is a sensor in the fuel tank somewhere. i'm not sure of the schematics for the newer Hyundais though. otherwise i don't know what's left to do. there might be a leak in one of the fuel lines. i had a smoke test done to determine where the leak was and low and behold it worked.

 

Im having EVAP problems in my tiburon.. after i replaced the PCV and the canister im still having problems.. drove it for 43 miles after resetting the ECU and the light comes on.. I need to get this junk inspected A S A P but cant because of my damn CEL.. Im about to just blow this thing up

 

yeah its a bastard to figure out and finding that sensor is only worse.



i should mention that it had pressure in the tank when i tested, i had just filled up. might try again tomorrow after i get home and bled all that crap out.

 

I'm not super positive on hyundais, but most evap valves (vent and purge) will always have key on 12v at the power wire and will open/close when the ecu switches the ground. Its tough to test evap wiring without a obd special tests tool being able to switch that ground for you.



If your sure its constantly staying open, it's possible that your ground wire has chafed is touching the frame or another ground source.





This is just from previous experience, i'm not sure if hyundai's work differently. I've just never had to fix evap on a hyundai before :biggrin:

 

wow actually thats actually very helpful, thank you. now i'm going to run the car with that valve removed but connected to determine if its passing or not. that could be the key!!



see, i know it won't pass with no power to it but its entirely possible that its passing with the 10V to it as you mentioned....and the voltage i was reading was the 10V! awesome!



this is why i like forums, i can get these little tidbits that allow me to reason the rest of the problem out



THANKS!

 

 

ok little more info and i'm hoping someone can confirm that this behavior i found isn't right and must be coming from the valve...



checked resistance on the valve, right in the middle of spec. 25.5 ohm. spec is 24.5-27.5.



next, removed hoses, left plug in and started car. valve didn't seem to budge. hooked up just the hose to the intake to apply vacuum to the valve. nothing seemed to happen at first....then started fluttering. had my pressure/vac gauge on the thing and left a vent so i could see what was going on....needle just bounces around. stethoscope on the valve is constant clicking on and off at idle....input voltage is 10.6-10.7. shouldn't open until 12V and the service info shows it can be as high as 14V to open and runs in 1Hz cycles....mine was a lot faster than that.



sounds like the valve for sure or any other things i should consider before ordering the part? thanks.

 

first off, what is the CEL code.

 

P0441 "evap emissions system incorrect purge flow"



also causes misfires that i usually can't feel on cyl. 1 or 4, sometimes random. i've narrowed it down to EVAP fumes being let into the intake at idle causing the misfires. at this point i'm simply trying to figure out if the cause is a faulty valve (appears to be) or if there could be a problem with the ECU. since voltage is quite stable, my guess is valve.