Mechanics

WHAT IS CAUSING A CHRONIC MISFIRE IN CYLINDER 3?

2002 Mazda Millenia • 116,500 miles

First tune up ever 3 weeks ago. New plugs, wires, cap, rotor. 3 days layer, engine light popped on and car was shaking. Codes read cylinder 6 misfire and EGR valve. Wire in cylinder 5 was bad, not 6. Wire and plug in 5 replaced again, EGR valve cleaned. A week later, light starts blinking and misfiring. Light goes solid then. Driving below 40 is hard. Back into shop. Cylinder 3 misfire. Plugs and wires replaced again, cap and rotor replaced again. Nothing. Needed car for work, so drove home. This was Tuesday. By Friday, no engine light, no misfire, nothing. Friday night, back to misfire, dropped car off for mechanic to look at. Got a call nxt mornigng all the sudden now I had a fuel injector leaking fuel everywhere! Never had ANY issues before the tune up. New fuel injector and leaking stopped. Still misfired. Cylinder 3 compression slightly higher than others, so engine and parts were decarbonized. Still misfiring in cylinder 3! All plugs wires cap and rotor replaced again. Still misfiring under 40mph. Mechanic had no idea what it could be. Then suggested it was electrical and to go to Mazda. I had not one of these problems before I brought it in for a tune up. What did they do to my car and how can I fix it? I cant keep driving while misfiring. Not only do I have a 3 year old in the car, but I dnt want to destroy my catalatic converter or crack anything. I need my car to make it at least another year or 2. HELP!
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Amandaspina
September 6, 2012.




So do you have any codes that current now?So it runs good above 40 mph?

Saturntech9
Sep 6, 2012.
Is the EGR code still present? I believe the EGR valve is located on the 3rd cylinder manifold and if that is the case, you most probably have a fault with it causing the misfiring on cylinder 3 at low speeds, meaning engine RPM would be below 3000.
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KHLow2008
Sep 6, 2012.
Thats what made sense to me just did know it feed the number 3 cylinder. Thats why I was asking about the codes and conditions for it. Happening.

Saturntech9
Sep 6, 2012.
When I picked my car up, the engine light wasn't even on. I still felt some misfiring, but still no light. This was Tuesday night. The engine light popped onyesterday morning, and I have not gotten the code read again. Seeing as how my mechanic said it was still misfiring after the EGR valve cleaning, I assumed the code was just for the cylinder 3 misfire. I will stop by advanced auto tonight and have them check it again for me. A friend of mine suggested it could be a nasty fuel filter, and I asked my mechanic and was told right away that it wasn't, because a fuel filter related misfire would occur in multiple cylinders, not just one. Still havent checked it tho. Driving to work this morning, I drove with a bit of a heavy foot. When departing from a stop sign, as long as I hit the gas a bit hard, it did not misfire much, maybe a little rumble. I noticed as long as I put a little force behind the gas, it does not misfire, even at a lower speed. Traffic is a killer however. It just seems like pushing down on the gas a bit hard gives a burst of air flow or something to possibly something clogged or closed up. Possibly an intake issue? Possibly still an EGR issue? My mechanic flushed out my intake and other parts with Run-Rite. He let it really soak in there to get rid of any carbon built up. If this turns out to be an EGR misfire code, how best to handle that? Replace entire vavlve? Will an EGR misfire still cause the compression issue in that cylinder? If its reads cylinder 3 misfire, what are my other options for the cause? O2 sensors? I was told everything else was good mechaniclly. I know what code to look for if it was catalytic conveyor related. Driving with a misfire will eventually lead to catalytic converter issues, wont it?

Tiny
Amandaspina
Sep 6, 2012.
Lets see what codes you may have first if you have any please post the exact code numbers not code descriptions. As far as the egr it wouldn't cause a compression leak. We may disconnect the egr valve to see if it runs any better but we need to check for codes first.

Saturntech9
Sep 6, 2012.
I will check code tonight after work and then post. Thanks!

Tiny
Amandaspina
Sep 6, 2012.
Your welcome keep me posted

Saturntech9
Sep 6, 2012.
And the verdict is in: P0303 cylinder 3 misfire. Kinda knew that tho. The guy at advanced auto said something to me and I really have the urge to curse out the guys who have been working on my car. He remembered me from the last time I was in there getting scanned (that is so sad). Gave him brief rundown of how many times parts were replaced in the past 3 weeks and he just blurted out "check your coils" I dont know why, but I guess I already thought my guys had done that and thats how they came to the "idea" it was something electrical causing the problems because everything else was mechaniclly sound. Very interesting. How would I know for sure it was the coil pack? I guess by process of elimination is one thing: plugs, wires, cap, and rotor had been replaced about 4 times within the past 3 weeks, fuel injector replaced after it was apparently stuck in the "open freely and just pour fuel everywhere" position. Which is odd because that was never an issue before! Im just mad that I try to get rid of raggedy 2002 plugs and wires and stuff and it has caused more problems. Could this misfire also be something electrical? I just want my baby running nice again. : (

Tiny
Amandaspina
Sep 7, 2012.
Another quick question - would resetting my ECU do anything, or no because of the drivability issues? Is the engine light coming on because there truely is a problem that is causing a continous misfire in the 3rd cylinder, or is the cylinder misfiring because the engine light keeps coming on ( ie: a short somewhere)

Tiny
Amandaspina
Sep 7, 2012.
If it is only the same cylinder that is misfiring, that should be much easier than random misfire.

EGR. If the EGR is not functioning correctly, it can sometimes not throw a code. The system itself is not faulty, just that it is working when it should not be. This can be due to vacuum leakages upseting the MAP readings. Check for vacuum leaks. Try disconnecting the EGR to test if the misfiring goes away.

The coil would not cause the same cylinder to misfire but the cap, wires and spark plugs would. Swap the spark plug with another cylinder. Ensure the wires are securely plugged in and if you are using after market plug wires, make sure the plug side wire has not been pulled in too far. They are prone to movements. Ensure the plug wire is routed well and not clamped by anything nor causing possible shortings.

KHLow2008
Sep 7, 2012.

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