Mazda3: PO304 Cylinder 4 Misfire? (Update: Sparkplug missing tip!)

[JEDI]

2005 Mazda3i 2.0L AT
125k miles

got a check engine light this morning:
PO 304 Cylinder 4 Misfire

Was going to replace the sparkplug, but which is cylinder 4?!

And any other suggestions for this CEL?


update:
bought new Iridium sparkplugs (same as old ones). when i removed the one in cylinder 4, i noticed it was covered with soot. then i noticed that THE TIP WAS MISSING?!!??!?!?!

Missing tip:

So have i damaged my engine?
the checklight only came on a couple of hundred miles ago, but what i thought was a slipping transmission has been occuring for the past 5k miles.

also, ALL the sparkplugs had lots of soot.

 

[bbs lm-r]

Cyl. 4 is at the back of the engine. In your case it'd the one closest to the driver's side.

You could also check for damaged plug wires. If you have a DVOM or something similar, you could check their resistance to see if their in spec. IIRC, should be about 4,000 Ohms/ft.

 

[Mxylplyx]

Might as well just replace them all. Might want to replace wires too.

 

[brblx]

look for carbon tracks or other signs of a damaged plug. compare the tip to that of the other cylinders, look for an an electrode that's eroded away or a bright, shiny ground.

i would replace all four plugs with OEM or the closest you can get at a parts store. (NGK platinum prolly). if it still misfires on that cylinder, it's probably the coil.

inspect the coil body for cracks, especially the plastic part underneath the windings that travels down the spark tube. also make sure the spark tube itself is clean and dry.

if it's missing constantly, you may have a wiring issue, but it's likely that it would set a seperate injector or coil code if that was the case. if it's intermittent, it's probably a bad coil. injector is possible but less likely.

 

[punjabiplaya]

upload some pics of the plugs. I'd def replace all 4 once you have one out

 

[JEDI]

upload some pics of the plugs. I'd def replace all 4 once you have one out

will do once i buy my spark plugs.

in the meantime i streched out the coil incase it somehow stopped making good contact w/the spark plug.

should i replace the sparkplug wires while im swapping out the spark plugs? 125k miles.
and does my car have a coil pack?

 

[JEDI]

another thought:
could a misfire feel like a transmission slip?
(for the past 5k miles it feels like my transmission has been slipping around 45mph)

 

[punjabiplaya]

not a slip, maybe more of a sputter/cough. I don't know of a better word to describe if anyone can think of something better.

 

[kornphlake]

Misfire could be described as surging or hesitation, like you press harder on the gas and it takes a few moments before the engine responds, then it surges ahead. You might also notice a rough idle, or roughness at speed, you may be able to hear one cylinder misfire if the exhaust goes pft-pft-pft-----pft-pft-pft----- pft-pft-pft----.

A slipping transmission would feel like somebody stepped on the clutch when you try to accelerate.

 

[brblx]

will do once i buy my spark plugs.

in the meantime i streched out the coil incase it somehow stopped making good contact w/the spark plug.

should i replace the sparkplug wires while im swapping out the spark plugs? 125k miles.
and does my car have a coil pack?

i think you have your parts terminology a bit off. the 'coil' that you stretched out is just a loosely wound spring that is used to conduct electricity between the output of the coil pack (that thing with the shiny epoxy on top that you removed to get the plug boot out of the cylinder and expose the end of the spark plug). the coil pack is essentially a transformer controlled by the ECM. it uses low voltage through a primary winding to induce high voltage in a secondary winding, which is what fires the spark plug. the car has four cylinders and hence four coil packs.

Misfire could be described as surging or hesitation, like you press harder on the gas and it takes a few moments before the engine responds, then it surges ahead. You might also notice a rough idle, or roughness at speed, you may be able to hear one cylinder misfire if the exhaust goes pft-pft-pft-----pft-pft-pft----- pft-pft-pft----.

A slipping transmission would feel like somebody stepped on the clutch when you try to accelerate.

pretty much, except that 'surging' and 'hesitation' are really two totally different symptoms. surging is mostly associated with engine performance at lower speeds- while it may idle poorly, usually an engine that is surging will have problems when making 90* turns, driving through parking lots, ect. the engine is under a bit of load with the throttle mostly closed, and some malfunction is causing the RPM's to vary, typically upward of the normal range. if the RPM's are simply dropping and the engine sputters then recovers, that's often due to something simple like a dirty throttle body. 'surging' implies more that the engine is speeding ahead when the RPM's should be dropping; and while quick fluctuations could cause the bucking and jerking often associated with misfiring, they're not the same. the latter is either a spark, fuel, or compression (engine mechanical) issue. surging is typically related to electonics issues with the air delivery (bad electronic throttle, flaky MAF, ect).

hesitation is simply an unresponsive engine, no misfiring implied, though a badly misfiring engine would certainly 'hesitate.' it's just that is can also hesitate without doing so, perhaps also due to an electronics problem, or something like an intake or exhaust restriction or low fuel pressure.

how bad is this car missing? if the check engine light has ever flashed at you, quit driving it until you find and fix the source of the misfire.

 

[JEDI]

update:
bought new Iridium sparkplugs (same as old ones). when i removed the one in cylinder 4, i noticed it was covered with soot. then i noticed that THE TIP WAS MISSING?!!??!?!?!

Missing tip:

So have i damaged my engine?
the checklight only came on a couple of hundred miles ago, but what i thought was a slipping transmission has been occuring for the past 5k miles.

also, all the sparkplugs had lots of soot.

 

[lavaheadache]

odd to see this thread, over the past few days I have been working on my moms 6 cylider mazda 6. She had multiple random misfires. Cylinder #4 on her car had the same issue. Ground strap on the plug was completely gone. Looking to do a compression test next

 

[LTC8K6]

Well, that missing ground electrode is somewhere. I'd want to look inside the cylinder with a borescope to see if it's in there and see if there is any indication of damage. Hopefully it just went out the exhaust.

 

[JEDI]

Well, that missing ground electrode is somewhere. I'd want to look inside the cylinder with a borescope to see if it's in there and see if there is any indication of damage. Hopefully it just went out the exhaust.

how did the ground electrode break off?

And why is there sooooooo much soot in all the sparkplugs? is there a way to easiliy clean the soot out of the engine?

 

[LTC8K6]

Not sure how it would have broken off. Hard to believe it wore out. Maybe it wore down to the point where it was thin and then broke off?

The soot is probably just from running a little rich and may not be anything to worry about.

You can do a seafoam treatment to try to clean the cylinder heads up. You will get arguments about the effectiveness of that, though.

I would not worry about it.

I'd look inside that cylinder and if it was clear, I'd put the new plugs in and drive on.

 

[Meghan54]

Not sure how it would have broken off. Hard to believe it wore out. Maybe it wore down to the point where it was thin and then broke off?

The soot is probably just from running a little rich and may not be anything to worry about.

You can do a seafoam treatment to try to clean the cylinder heads up. You will get arguments about the effectiveness of that, though.

I would not wory about it.

I'd look inside that cylinder and if it was clear, I'd put the new plugs in and drive on.

I know the Seafoam treatment does do an excellent job in cleaning carbon buildup and freeing up the rings in an outboard engine. One of the most recommended treatments for outboards. I trust it.


As for the grounding electrode missing....very odd. I'd take it somewhere and have the cylinder bore scoped, as others have suggested. A bit of metal bouncing around in a cylinder can have no good consequences.

 

[kruss]

I know this is an old thread, but I'm having the exact issue in the exact cylinder. I have a 2004 Mazda 3 2.3L. Did you ever find a solution to your problem?

 

[JEDI]

I know this is an old thread, but I'm having the exact issue in the exact cylinder. I have a 2004 Mazda 3 2.3L. Did you ever find a solution to your problem?

nope

car was at 125k miles when I created this thread about cyl #4 was eating the ground prong of the spark plug.

I just left it in there.
my car is at 200k miles.

car is rated 34mpg hwy.
i still get 32mpg in 70% hwy/30% city driving.

i have NO IDEA how cyl #4 is working w/o a ground prong, but it's not affecting my gas milage or operation of my car.