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Discussion Starter · #1 ·
I’m getting a P0304 Code - Cylinder #4 Misfire code on my 2001 SEL. I’ve seen the various threads on this issue on how to trouble shoot it. However, I’d like to know, how serious is this problem? The only symptom I’ve noticed is that the car occasionally runs rough when idling. Otherwise, the car runs fine. Is this something that needs to be addressed immediately, at risk of ruininng the engine? I do intend to deal with it, I just may not be able to get to it until two weeks or so, but I drive the car 50 miles every day. I’m also aware that I’m using only 5/6 th’s of the engine’s power and probably wasting gas. Thanks.
:(
 

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the cats are already 10yrs old. with the unburned gas getting dumped into it there really isnt telling how long it will last. the fix might be easy, a plug/wire.
There are cars that drive for months on a misfire with no issues. But i have been burned in the past with the cat getting clogged from one.
 

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Discussion Starter · #7 · (Edited)
Okay, I replaced the spark plug, no resolution. (Noticed what appeared to be a drop of possibly oil on the spark plug tip? Not sure if oil or gas.) I replaced the wire to that cylinder, no resolution. Next step, I’ll change the coil. If changing the coil doesn’t work, next step check the fuel injector (groan)?
 

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Discussion Starter · #10 ·
Okay, changed plug, no resolution. Changed spark plug wires, ditto. I replaced the coil last night. Keeping fingers crossed for the test drive this morning. I got held up on changing the coil since my 2001 24 valve duratec SEL was blessed with Torx bolts affixing the coil to the engine block. Oh goodie! So had to run out and buy a Torx screw driver set. The previous posts said it was size T25 or T27. It was 25 on mine. I had no problem doing it once I removed the cowl covering over the cabin filter.
 

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Discussion Starter · #11 ·
Okay, drove car this morning and ... still getting the cylinder four misfire code. On to fuel injector Saturday.
 

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Are you turning off the light ea. time you replace a part with a scan tool or by disconnecting the batt. neg. (ground) cable for a few mins.? Now would be a good time to check/replace upper and lower intake manifold gaskets. Are you going to swap 4 and 5 injectors to see if the misfire code jumps to #5 cyl. or replace it? May end up needing a compression and leak-down test.
 

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Discussion Starter · #13 · (Edited)
Sheila and FOTRD, thanks for the heads up on the gaskests, will do. I'm just gonna replace the injector, not gonna open up UIM twice! (First time with UIM).
 

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Discussion Starter · #14 ·
Okay, I swapped out the UIM and LIM gaskets and the fuel injector at cylinder 4. Took a few test drives and no codes yet. However, there is still a moderate smell of gas from the exhaust. Could it be my catlytic converter is already shot? I'm not getting any codes for the the CAT converter. By the way, the first time I closed up the UIM, gas started squirting from underneath the hood. Opened it up again and turns out the O ring for cylinder six was torn. So I replaced all the O rings and no problem next time starting the car.

If the CAT converter is shot, does it affect engine function? I'm not concerned about the emissions inspection.
 

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Okay, I swapped out the UIM and LIM gaskets and the fuel injector at cylinder 4. Took a few test drives and no codes yet. However, there is still a moderate smell of gas from the exhaust. Could it be my catlytic converter is already shot? I'm not getting any codes for the the CAT converter. By the way, the first time I closed up the UIM, gas started squirting from underneath the hood. Opened it up again and turns out the O ring for cylinder six was torn. So I replaced all the O rings and no problem next time starting the car.

If the CAT converter is shot, does it affect engine function? I'm not concerned about the emissions inspection.
the cat has to warm up first, before the gas smell goes away. if you are still getting the smell of gas after driving the car for 15 +min the cat might be soaked. It might just burn off and the smell will go away with no issues.
A clogged cat will do a couple of things. The car will run sluggish for 1. a good way to tell is to drive the car till you are at normal temp at night. then take a look at the cats and see if its glowing.
I would drive it like normal and see what happens.
 

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Discussion Starter · #16 ·
I spoke too soon. Drove the car this morning and the cylinder four misfire code popped up again. So, on to the compression test and leak down test ... May be looking at big bucks if it’s the piston rings?
 

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I got this same misfire except on my #3. I changed everything spark plugs, coil pack, and wires. So for 6 months nothing then got the same misfire. I am still getting 25 to 26 miles to the gallon. the mechanic i take it too cannot figure out what is happening. I figure it is just mileage on the vehicle 200k.
 
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