Civic HX misfire P0303
11-07-2013, 07:03 AM
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Civic HX misfire P0303
Hi All,
Have a 98 civic hx with around 200k miles. It has been running well, but lately my girlfriend complained of hesitation going up hills. I have cleaned out the EGR system before, and checked it again last night. It was badly plugged again. So last night I:
-Cleaned EGR valve and ports
-pulled the spark plugs and checked them, all look healthy
-checked compression across the board (185-190 on all cylinders)
Took it for a beat and it ran very well, could not get it to misfire at all, no CEL. She called again this morning and said it was again hesitating going uphill, no CEL though.
I gave the car a full tuneup about 35k ago, new 02 sensor, new NGK plug wires, new NGK plugs, cap and rotor, fuel and air filter, set timing etc.
I did notice that there was a little discoloration on the bottom of the spark plug porcelain, and the bottom of the spark plug boots. Not sure if it was abnormal or not, looked about even for all cylinders.
Not sure where else to go here, I am going to adjust the valves tonight because i have never done it on this car. Is there anything else obvious that I am missing? Strange that it misfires and won't give a code all of the time.
On a side note, the car did get overfilled with oil a few months ago. I think she ran it this way for maybe 2 or 3 days before i caught it and drained some oil back out. This is why i thought to clean out the EGR passages again, figured burning extra oil could have plugged them up faster. Not sure if there is anything else this could have messed up.
Have a 98 civic hx with around 200k miles. It has been running well, but lately my girlfriend complained of hesitation going up hills. I have cleaned out the EGR system before, and checked it again last night. It was badly plugged again. So last night I:
-Cleaned EGR valve and ports
-pulled the spark plugs and checked them, all look healthy
-checked compression across the board (185-190 on all cylinders)
Took it for a beat and it ran very well, could not get it to misfire at all, no CEL. She called again this morning and said it was again hesitating going uphill, no CEL though.
I gave the car a full tuneup about 35k ago, new 02 sensor, new NGK plug wires, new NGK plugs, cap and rotor, fuel and air filter, set timing etc.
I did notice that there was a little discoloration on the bottom of the spark plug porcelain, and the bottom of the spark plug boots. Not sure if it was abnormal or not, looked about even for all cylinders.
Not sure where else to go here, I am going to adjust the valves tonight because i have never done it on this car. Is there anything else obvious that I am missing? Strange that it misfires and won't give a code all of the time.
On a side note, the car did get overfilled with oil a few months ago. I think she ran it this way for maybe 2 or 3 days before i caught it and drained some oil back out. This is why i thought to clean out the EGR passages again, figured burning extra oil could have plugged them up faster. Not sure if there is anything else this could have messed up.
11-07-2013, 08:02 AM
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Re: Civic HX misfire P0303
i suppose i should add that the exhaust manifold has a crack near the o2 sensor bung. I welded it up a year ago, but i noticed its leaking again. There is definitely some leak there, but not enough to hear it. Not sure if that can cause this symptom or not.
11-11-2013, 08:10 AM
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Re: Civic HX misfire P0303
well, i checked all my valves, they were all pretty much spot on, re-welded the manifold crack, and it still has a bit of a hickup just as you tip into the throttle and leaves slight haze of black soot on the rear bumper. Going to replace the primary 02 sensor next. Damn thing is hard to diagnose, not giving any codes currently.
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