Something I catch with my ear that ECU's* cannot. I listen with a screw
driver or my favorite socket which is larger than most people's breaker
bars. It's large and it reduces the volume of outside noises. I close
the ear flap of my ear with one end to also deaden outside noises. I
listen to each spark plug as best I can - of course with them all
running.
Whichever sounds brighter is typically running strong
enough or "on time". Whichever is sounding duller is late or weak. If I
can't listen on the spark plug coil or wire, I'll listen as close as I
can to the combustion chamber. Sometimes on the intake side, sometimes
on the exhaust for where I can reach.
Coils that are bad can make
a little electric crackle. The test above is comparable to an ECU
counting misfires on a cylinder, except that it catches much smaller
problems that may not come up as a misfire yet. It may not be bad
enough. It, like the computer check for misfire can't distinguish
between spark plug wire or coil on spark plug setup, not for sure what
cylinder is misfiring.
Like I listen for a misfire the computer
can mistake an echo. When I'm evening the spark out across an engine on a
V engine what sounds bad on 1 bank may be a problem coming from the
other bank opposite of the cylinder on the V. If in the firing order the
previous cylinder doesn't have good enough spark, the next cylinder
will sound weak when it may have been strong.
Long story short,
this is why ECU's can get which cylinder is misfiring wrong. This video
has a very effective way of ruling out more than one problem at once.
Logically, I recommend it in a coil on spark plug setup over a spark
plug wire to spark plug setup, as the chances of mixing up spark plug
wires is much higher.
Thank you for inspiring this article Shrodinger's Box:
P0304 misfire Quick Diagnosis with just CodeReader-no scan tool
by AutoBravado
On my own cars and trucks, I usually get rid of a "misfire" before it's significant enough to show up as a check engine light issue. I'm making engines run smoother, and it really is a bit of a misfire, but not enough for the PCM to declare emergency with a blinking Check Engine Light (CEL). I show these techniques here:
