2004 Accent - auto. - 100K miles
Ok fellas, some you have seen my posts dealing with my CEL for code P0304. I thought I had it solved but now it comes on after every fuel fill-up. Its happened at least 5 times or more. I know what the code means (ign. misfire #4 cyl.).
I read and checked what affects the code but this one has me baffled. I thought at first it is the evap. canister but the car takes a fuel fill-up without any trouble and it is not hard to pump it all in and does not give me the code. If I put a bottle of STP gas treatment in the tank it clears the code after about 40 miles drivieng but it doesn't explain why it sets off the CEL on every fill-up. I also thought I may have sediment in the tank and the fill-up is stirring it up but I have filled her up and various capacities. Also, several weeks ago I got the CEL code P0441 for the purge control valve. I replaced it, cleared the CEL and it never came back on. Fuel filter has never been replaced because it is built into the fuel pump assembly.
Overall drinvability and MPG's are not effect. Any thoughts fellas....

Anyone wanna try and guess? CEL goes out around 2/3 of a tank of fuel.

The fuel filter IS replaceable, even though it is in the tank. It's not "built into" the fuel pump, but you do have to do some disassembly to get to it.

It sounds as if you may have bad gas or sediment. I'd change the filter and maybe start using a different gas station.

I've ruled out the bad gas since my wife uses different gas stations and it has happened several times. And I would think that the CEL would stay on and not go off if the fuel filter is clogged. When the tropical storm HANNA settles down I'll look at the fuel filter for a replacement. Thx...Anyone else?

i may not be 100% mechanical minded but if its saying "ignition mis-fire" have you checked your distributor, plugs and points? sounds kinda simple but it could just be the problem.. Does this fault affect driving? also, How did you first discover it? Last suggestion is a fuse has blown on the fuel delivery circruit / Bad ECU

Same problem here. I already put in new plugs, and coils and it didn't make a difference. Today I replaced the ignition wires with new Bosch set, and the same error code came back on.

I wouldn't think it would be a fuel filter, since it's always the same code, misfire on 4th cyl.

Any ideas???

since you already did plugs/wires and coil the next thing I would do is unplug the wire to the injector and see if the engine starts to stumble. If it doesn't you have a bad/clogged injector.

Yup, my wife's '04 Accent sputters after each fill too. And we also have the p0304 "misfire on cyl #4" code. Replaced all ignition wires, plugs, etc. What to do????

This post has been edited by strtbobber: Jul 14 2009, 01:13 AM

Replaced injectors, checked compression and still doing the same thing.

Anyone?

ok, my two cents worth. my 2004 accent with 82K miles is doing exactly what yours is doing. it has been going on for a year and it is killing me. i also had a 0304 code and an 0441 code. the dealer said repalce purge valve; i did; the 0441 code is gone. however. everytime i fill it up, the cel flashes about 25 times and then stays on and i get an 0304 code. the plugs and wires are new hyundai parts. the spark from #4 is very strong, just like the other three. the #4 fuel injector clicks regularly and well with a mechanic stethoscope, just like the other three. the cel light frequently goes out after about 1/3 tank is gone, after sitting overnight.
here's my theory: this all started when i began getting gas at a station that used those accordion type collars on the pump nozzle. i think that those pumps really push in the fuel under extra pressure, and that my canister cannot handle the load. therefore, two weeks ago, i started going back to my old station, where there is only a loose splash guard on the pump nozzle. lo and behold, yesterday morning, after the second fillup, the cel flashed 25 times, but then stayed off, whereas for a year it always stayed on. this is the first and only time in a year that i did not get the cel staying on after a fuel fillup and after the 25 flashes. i do not know if this is a cure, but i think i am on the right track.
therefore, i am having a friend try to get the entire canister assembly off of a junker, with all hoses and with the white plastic attached electric control module. i will switch the used one with mine [10 minute job] to see if there is any improvement. in any case, things did get noticeably better for me when i went back to the old style splash guard fuel pump.
final thought: is there any pattern here with users of gasohol? my state of wisconsin is a gasohol state. perhaps all people with this problem are gasohol state people.

ok. got back from vacation and replaced the entire canister assembly with a unit from the scrap yard. it made not one bit of differnce in this problem.

now, i have noticed that when my car is first warmimg up, there is no mis-fire. it is when it is warmed up that i get problems. for instance, when i recently drove to wal-mart, the car ran great. i parked. i shooped for 15 minutes. when i came out and started it, it ran lousy, with a good deal of mis-fire.
i told this to my mechanic, and he suggested a leaking injector as a possibility. does anyone have any toughts??

I don't see how it could be a temp related problem. 15 minutes should have been enough to cool the engine.

Pretty sad how many people have reported this issue and it seems that no resolutionm has been found still.

I was going to replace the filter today, and it looks like the service manuel and online parts catalog was wrong. There is no filter under the rear seat cover, and it's in the pump assembly. WTF.

Tomorrow i'll change the evap valve, and crank position sensor. This is going to be the last two items, other than changing the ECU or engine computer ..

Sounds to me like a fuel pressure problem. I'd be changing the fuel filter. If that doesn't work, I'd be checking the fuel pressure somehow.

Yeah, hmaservice shows the filter under the seat. See pic. Others have also said it's actually part of the fuel pump assembly. Here's a link to a nice DIY for Elantra fuel filter for the same period:

http://www.elantraxd.com/DIY/fuel.php

Looks like fuel filter is OUTSIDE the tank as shown in the diagram. Did you pull out the back seat and look at it?

http://cgi.ebay.com/ebaymotors/Hyundai-Acc...sQ5fAccessories

It's not outside. That's the wrong filter for the 04 accents. I pulled the back seat, and under the cover there is a fuel pump assembly only. There is no filter, at least not the one like in the ebay link (same thing many other retailers sell).

If it was a fuel pressure problem wouldn't there be random misfire codes, and not ONLY p0304?

You would think it's a plugs & wires problem, but he's only complaining when he fills the gas tank. It's possible fuel doesn't get to #4 somehow. Maybe the injector is bad, maybe fuel pressure is low and fuel injector is dirty?

This post has been edited by jsinton: Nov 29 2009, 09:41 AM

I have the same problem with mine, replaced injectors (coils, wires, plugs and checked compression) and it made no difference either (mpg did go up a little bit).