what country? what engine, USA is 2.0L chain cam.
7 engine world wide,?
my wild guess is uSA as 2002 cars in many countries
have no OBD2. till later.. no 303 to show. my weak guess,....
it's means , ONLY that #3 misfires. ( P0303 not just spark )
there are lots of ways to misfire. huge.
but here they are. (some)
1: bad spark to #3 (cop? coil swapped, got 4 coils or 2 or ?)
no country stated, some have wasted spark with 1 cops per pair of cylinder i presume its 4 COP 4cylinder engines.
2: bad injection #3 (injector clogged or weak, or bad conn, to ECU.
3: weak compression to #3
4: coolant leaks to #3
5: valves sticking on #3 (or oil leaking past valve guides #3)
6:Does the spark plug re-foul, yes/no?
is that fouling (if true #3) oil , water, green, or fuel soaked?
color of spark tips are a huge clue, learn to read them.
in most cases, guessing never works, you need to do tests.
start with compression. at spec. all cylinders. are they equal.?
Does the strobe light show, misfire at idle?
is the fuel trim in OBD2 looking ok , near zero . Long term fuel trim.
"LTFT" mine runs -4% not -40 rich or +40 rich
are there only 303s, no others?
is the engine ECU holding closed loop at idle and light flat cruise?
you do ,know all engines have 1 weaker cylinder, (marginal)
and if fuel mix is off, the weakest cyl ,fails first
so ignoring fuel mix above, fails to find a real culprit.
closed loop. does closed loop hold?
keep in mind this.
the ECU detected a weak power stroke on #3.
it has no idea at all why , only that its 100% true ,that fact..
well, if the cam is not bouncing.... rare, if chain , common with belt drive. then that too can show misfire in very odd ways.
(cam and belt bias , facts are complex but can show up ,in odd ways. turn a cam head off, and feel that bias. this fact add to the belt or chain bounce and cat favor a cylinder or a tad weak one.)
so if the belt or chain bounces, oops. (the chain will yell , im bad)
didnt try to look up which motor you have., so chain or belt.
of stated suz. engine type.
2 liter? or 2.3L? j18/20/23? its called.
no miles stated, 100k ,300k? what?
the chains can fail about 120k, and the tell you,
the WIKI worldwide, shows
1.3 L I4
; 1.5 L
I4; 1.6 L I4; 1.8 L I4; 2.0 L I4; 2.3 L I4; 1.4 L Diesel I4