flashing cel


Old 10-24-09, 02:41 AM
Thread Starter
Join Date: Oct 2004
Location: wisconsin
Posts: 135
flashing cel

2004 hyundai accent 1.6L; 82K
for almost a year, this happens everytime i fill'er up. i always stop at the same gas station and take about 10 gallons. i already put on a new fuel tank fille cap.
as i pull away from the station, the cel flashes about 25 times and then stops for a few seeconds then flashes about 25 times again and then it stays on. during this time, the engine runs noticeably rough [for the old guys, it runs like a warm car with the choke on]. after i enter the freeway and drive 20 minutes, it runs smooth again, but the cel stays on. the only code is P0304 [cylinder 4 misfire]. the plugs and wires are new hyundai parts. i clear the code and the car runs ok until the next time i fill it up. no-one has the slightest idea as to what is going on. any thoughts.
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Old 10-24-09, 09:19 AM
Join Date: Oct 2009
Location: MO
Posts: 10
Sounds like you may be overfilling your tank which overloads the evaporative control system until you've used some gas out of the tank. When refueling stop filling the tank as soon as the nozzle clicks off the first time.
Old 10-25-09, 03:28 AM
Thread Starter
Join Date: Oct 2004
Location: wisconsin
Posts: 135
thanks. i was kind of thinking the same thing. the station i always go to has some kind of accordion rubber cushion on the nozzle that really seals the filler. that seems to drive all the vapors into the tank.
today i filld it up at a staion that just has a splash guared at the end of the filler nozzle [some vapors escape into the air]. no problems at all with flashing lights and rough idle for the first time in a year. no CEL-hooray.
i think you are correct.

while we are on a roll, can you tell me what happens when the canister control valve fails to functions properly? that is the only device i can see on my system other than the canister itself, and the fuel tank air filter.

finally, if everything is ok with the evap system, are you supposd to hear air rushing when you loosen the fuel tank cap? i hear nothing when i loosen the cap.
Old 10-25-09, 05:14 AM
the_tow_guy's Avatar
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Join Date: Feb 2001
Location: SW Fla USA
Posts: 11,515
You should get the codes read to see what's up. Normally a problem with the evap system will light the light but not make it flash. A flashing CEL is a warning sign that you have a more serious problem than just something like a loose gas cap or overfilled tank and could be doing damage; the catalytic converter is a candidate for damage when you have a misfire sufficiently bad to flash the CEL. Check with AutoZone if there's one near you; they will usually do a code read for free.

Some reading material on the system:


Emission Control Systems
Old 10-26-09, 10:47 AM
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Join Date: Oct 2004
Location: wisconsin
Posts: 135
thank you. i learned a lot form the link.

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