P0300 code misfire p0303

when did car last run ;perfectly? last month, last year, or don't know?
p0300 means all fail randomly (is the key clue here.
there are only 3 causes (engine,spark ,fuel) (bad list)
the P030x errors are all , bad combustion errors.
that means,
can be lean burn, misfiring or way way too rich or bad fuel.(old)
or weak compression on all cylinders below 150PSI WOT
bad spark on all. (spark must be good on all)
1/2 clogged injectors on all..(or some fail leak down tests)
so did not check LTFT, long term fuel trim?
check fuel pressure? to low or too high and not in spec range.
I bet P0300 pending's is not a lie.
most cars need to be hard driven to see all DTC possible.
some take 3 driving cycles to trip. so drive way tests are very limited.
is engine coolant at 180f hot? or more hot, if not thermostat is bad.
as all are that old if is.
24 year stats are junk now. even non linear or even stuck open/
stats that old fully capable of even being INTERMITTENT.
Scan tool hot. ECT = 180F? PID scanned, Ect.
only used real scan tools not $17 useless code readers,
the real too can scan any sensor on demand. called PID scans.
and see pendings never forget to check pendings.
at 180f hot engine does scan tool; show CLOSE loop status?
it must, if not fix that first. (and p0300 for sure)
front 02 sensors bad.
302 means cylinder 2 misfires, but I bet the all do if car driven hard and scanned at the same time. I never just scan parked, drive it hard.
if lean power will be horrible weak.
not told at all how it drives. and matters huge, what is seen odd.

we can't tell you what you can do, lacking skills and tools and spares.
I can tell you what a shop does. sure.
P0300 means all cylinders of the engine are missing,
means (physics) weak combusting on all cycl.
bad spark all or bad injections to all (lean) or engine cam out of time?
P1 codes are factory only codes. Jag codes
P1000 means car is not ready for smog tests, the , onboard readiness is not complete, means drive for a day or 2 and is caused by scan tool DTC reset or battery on car went dead or was disconnected.
next P1316 _
Misfire Excess Emission, get the shop to find it.
there are a battery of test to do.
even low fuel pressure can trip p0300.
goes lean ,combustion goes weak and BINGO gross misfire.
or bad spare, but how can all fail and not get one cmp or ckp errors>?
bad fuel> too. put diesel in the gas?
park parked over 1 year or parked less, with 1/8 tank for long long months?
we can not guess history of any car.

Yes a misfire could cause a false 02 code. As far as why it's misfiring could be a plug and wire issue but hard to say without looking at it

code p 0420 refers to cat converter system bank 1---efficiency below threshold====causes ---cat converter---wiring---HO2S (heated oxygen sensor, the one in the exhaust manifold before the cat converter)
code p 0300 is random misfires
I would suggest changing the HO2S as it reports to the ECM on exhaust content so that the ECM can adjust the air/fuel ratio
so it is logical that if that unit is not reporting correctly, the cat converter may be having trouble burning off the gasses correctly
The oxygen sensor(O2S) reads the results of the cat converter operation and helps fine tune the ECM settings

MULTIPLE MISFIRE CAN BE CAUSED BY.CLOGGED FUEL INJECTORS.ADD A CAN OF SEAFOAM TO A 3/4 TO FULL TANK OF GAS.CHANGE FUEL FILTER, IF ALL READY CHANGED SPARK PLUGS AND WIRES.A WEAK FUEL PUMP AND A CONTAMINATED MASS AIR FLOW SENSOR WILL CAUSE LEAN MISFIRE CONDITIONS.

P0300....Random/Multiple Cylinder Misfire Detected

i would suspect either the coil pack or the leads ,also make sure spark plugs are set to 25 th as too wider gap could cause this problem as well

Any time there is a misfire condition in an engine the o2 code will pop up,so you need to correct the misfire and that code will go away.To repair the misfire i would first try a new spark plug and then the coil for that plug.It could also be a faulty injector on that cylinder but that is not common,go with the plug first.note;all the plugs are the same age so if this is your problem,replace the rest also.

The code is a mis-fire code. This code does not tell you which cylinder is mis-firing.
Here is a list of other items to check :

- O2 sensor
- Catalytic converter
- EGR valve
- Cam sensor
- Bad computer

Please let me know what you find.

I have a 2000 Oldsmobile Alera that has a diagnostic code p0300 random misfire, runs very bad change- ignition coils- spark plugs and boots for plugs. change catalytic converter, and fuel pressure is 50 to 60 lb. And my car still runs the same, HELP HELP HELP!!!!!!!!!!

well the codes
p0300 multiple misfire
p0303 misfire cylinder 3
p0304 misfire cylinder 4
p0307 misfire cylinder 7

can be alot of things check cylinders for compression is what i would do first..