Why is cylinder 2 misfiring?? even stumped a mechanic
Day 1: Knock sensor 2 code was active (but the car has a light knock when
over-revving). Noticed the car was running pretty rough, with a lower than
normal idle RPM. Also notice it got rougher once I reached 40mph on
fourth gear. Then noticed oil pressure light was flickering occasionally
(went to a forum where everyone said the oil pressure light was likely
sludge or particulates clogging the oil intake screen). So I used the ZMAX
fuel system cleaning kit, which came with an engine oil treatment, fuel
system cleaner that was sprayed into the intake and fuel additive. I drove
for about 100 miles, during which the oil pressure light turned off. Then
after driving, I removed the oil pan, cleaned it, scrapped off all visible
sludge from bottom of engine in the oil pan area, then scraped all sludge
and deposits off the oil intake screen (which was very thick). Also did a full
oil change with full synthetic oil and new filter.
Day 2: car has been running much smoother for about 2 days. then check
engine light begins to flash at me along with the oil pressure light
intermittently, as well as rough idle and high speeds began again. So just
in case i performed another oil change using a detergent, as well as
flushed clean oil through the system to make sure all detergents are rinsed
out and replaced filter again. This took care of the oil pressure light again
(think i got it all this time lol). As for the check engine light, I had the codes
checked which showed an evap system leak, knock sensor 2 and cylinder
2 misfire. by an amateur mechanic friend, I was told that the evap system
leak could be the cause of misfire. So I searched the evap system and
found a vacuum hose that was disconnected from the air filter housing. I
reconnected it and waited till morning to check if the codes had been
remedied.
day 3: took car to autozone to have codes pulled. This time the evap leak
code is gone, however cylinder 2 is still misfiring and now cylinder 6 is
misfiring. got new plugs and replaced cylinder 2 and 6 plugs. cylinder 2 old
plug was caked in black carbon deposits and even appeared as though
the arching metal on engine side of plug had been slightly warped.
Cylinder 6 plug was immaculate aside from a light layer of white ashy stuff.
Then checked codes again. Now only knock sensor 2 and cylinder 2
misfire.
day 4: troubleshooting the misfire, I know the spark plug is good. I also
switched up coil 2 (on misfiring cylinder) with coil 4 (a known good
cylinder/coil/plug/wire/injector). The misfire did not follow the coil, so I know
the coil is not the issue. Then pulled cylinder 2 plug out, connected it to
boot and tested to see if spark will arc from the plug (effectively testing the
plug, the wire and the coil) it sparked very strongly. So now I'm down to
injectors. I did the same process of switching the "questionable" injector
with a known "good" injector. The misfire did not follow the injector.
conclusion thus far, I have a knock in the engine, so ofcourse the knock
sensor is throwing a code. Cylinder 2 is misfiring. Cylinder 2 ignition coil,
wire, plug and injector is working properly.
Question: Why is cylinder 2 still misfiring, despite tests indicating the coil,
plug, compression, wire and injector are good?
