misfire code p0304 help please

Guvy

Member
I have a 2002 Protege5 with about 64K on it, I am the original owner and have been doing pretty much all maintenance myself.

It all started a couple of months ago. My CEL came on for the first time.
I had the codes checked at Auto Zone and it said P0304 Cylinder four misfire.
1- So I looked at the spark plugs (NGKs) ($10)and indeed number 4 looked really bad. So I changed the spark plugs and reset the ECU and the light went away for a few days and came back again.

2- I thought, OK time to change the original plug wires. CEL went away for a day or two and came back. ($65) (pissed)

3- Time to change the Coil Packs, ($90) I thought. No help, and the light came back again.
4- Removed, cleaned and replaced the EGR valve. No help
5- Complete Fuel injector Cleaning.($59) No help
6-Changed the #4 Fuel injector itself.($110) Samething.
7- Removed fuel pump and cleaned the "fuel filter". No help.


When the light comes on: I feel the car is very sluggish. It struggles to maintain speed and feel like I am dragging a tractor behind me.
When I reset the light, the car feels completely normal and drives just fine. Also when the light is on the engine sputters and shakes like it wants to stall.

I am running out of options. I'd hate to take to a dealer and have them rape me.
PLEASE HELP!!! Anyone else had this problem? and what did you do to fix it ? Any idea is welcome.


Thanks.
 
Maybe a problem with the plug for the #4 injector or the wires leading up to the plug. Is the spark plug still coming out looking bad? If it is I would swap the coils and just double make sure the problem doesn't follow the coil. If the problem still persists on #4 then we can start looking at other things. What did the plug look like? Was it oil fouled or white? Got any pictures?
 
xelderx said:
Maybe a problem with the plug for the #4 injector or the wires leading up to the plug. Is the spark plug still coming out looking bad? If it is I would swap the coils and just double make sure the problem doesn't follow the coil. If the problem still persists on #4 then we can start looking at other things. What did the plug look like? Was it oil fouled or white? Got any pictures?

-I had all 4 injector wires tested using I little light tool, I'm not sure what it was exactly. (auto-zone guy did it for me)


-Number 4 Spark plug WAS actually "oil fouled" with a lof of gummy build up.
I will try the coil swap idea.
any other ideas, or anybody who went through this and found a successful solution? It is very frustrating.
 
Last edited:
Guvy said:
It WAS actually oil fouled with a lof of gummy build up. I will try the coil swap idea.
any other ideas, or anybody who actually went through this?

http://www.verrill.com/moto/sellingguide/sparkplugs/plugcolorchart.htm

"Too much oil is entering the combustion chamber. This is often caused by piston rings or cylinder walls that are badly worn. Oil may also be pulled into the chamber because of excessive clearance in the valve stem guides. If the PCV valve is plugged or inoperative it can cause a build-up of crankcase pressure which can force oil and oil vapors past the rings and valve guides into the combustion chamber."

have you tried the PCV valve? that would be an easy, cheap fix to try...
 
PCV valve is pretty new. I change it every few oil changes just to make sure.
also. I am not loosing any oil between changes to suggest I am burning/losing oil.
 
The plug is fouling with oil somehow. We need to figure out where the oil is coming from. That is probably where why you are getting a misfire. The sparkplug can't fire properly when it is fouled like that. You could try to go one heat range hotter on your plugs, but that is really a bandaid for the real problem. I had the same problem 2 years ago with mine and ended up having to rebuild the motor,. The rings were just shot and it was fouling the plugs.
 
xelderx said:
The plug is fouling with oil somehow. We need to figure out where the oil is coming from. That is probably where why you are getting a misfire. The sparkplug can't fire properly when it is fouled like that. You could try to go one heat range hotter on your plugs, but that is really a bandaid for the real problem. I had the same problem 2 years ago with mine and ended up having to rebuild the motor,. The rings were just shot and it was fouling the plugs.

ouch, that's a pretty uncommon problem, and probably not what this guy wants to hear. :(
 
Kansei said:
ouch, that's a pretty uncommon problem, and probably not what this guy wants to hear. :(

It could also be a valve seal, but I've never seen the valve seals just go bad. It doesn't sound like an easy fix at all. Oil fouling a plug means the problem is inside of the motor and not something bolted to it usually.
 
you guys are scaring me. I am hoping it is not as serious as what you're describing.
I did the MAF sensor cleaning this morning, swapped the coils and reset the ECU.
I will keep my fingers crossed and wait.
 
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