hello there,
i know this is not the first time anyone asks this question and how to deal with it. i've seen almost all topics did what they said still not gone.

bought a C6 2006 coupe. had a P0300 missfire code which stands for multiple missfire as we all know.

so in order to solve the problem i replaced the spark plugs with the wires. i used AC delco spark plugs from the dealer as well as AC delco wires 41-110.

after doing this went out and still felt the missfire and the code still there, asked several mechanics what could cause the problem they kept saying plugs, wires, coils and could be a bad oxygen sensor with a clogged catalytic converter. So what i did what was buy Dynatech headers and installed them today (very impressed honestly and eventually i was going to get them) by that way i got rid of the catalytic converters for good. still didnt take it to a tuner/computer programmer to turn off the check engine light, but i still have the missfire.

the question is, what could cause a P0300 code if i have new plugs, wires and no catalytic converter/oxygen sensor.

do u think i should replace coils or is there anything else to be checked?

i just hate driving it with a missfire, since i bought it i drove it to the garages only.


thanx in advance.

UPDATE: READ MY LAST COMMENT IN THIS THREAD ON HOW I SOLVED THE MISSFIRE.

 

dcould be a crank or cam position sensor. these monitor for engine misfire as well.are any other codes present?excessive vibration from sources other than the engine can cause misfire such as brake rotor wear,worn or damaged drive belt and driveline vibration.good luck finding it.do a crankshaft position system variation learn procedure before trying to diagnose

 

Any Tech with a good scanner can go in on the Misfire Monitor and see which Cylinders that are Missing firing... I do that first... Find the Cylinders that are missing... Do a Compression Check... If Compression is good swap a known good coil to those cylinders that are missing and see if it goes way... If coils don't solve it.. Start looking at possible Injectors...

 

check fuel pressure and compression. what did the plugs look like? when did the problem start? are you using any coolant ?

 

there is a knock sensor error but i guess its related to the missfire.
all brake rotors are perfect, engine and trans. mount in very good condition. dirve belt is good. a mechanic told me could be caused by crankshaft position sensor. i guess i'll be replacing it.

 

i tried several scanners all show P0300. P0300 stands for multiple missfire. if it gave me P0301-P0308 the last digit stands for the cylinder number.
tried that before with no use.compression check done. its good, perfect in fact.

 

honestly i just got the car, i flushed the radiator added dexcool to it. i even cleaned the injectors but still the same problem

plugs were replaced few days ago with the wires. i took the parts based on my chassis number from the dealer.


this missfire thing is giving me a hard time. my plan was get the car do a major service which i did. i had a list for mods i have some and ordered some but i may throw the list out for a while.


took it to the tuner/computer programmer. he says this missfire is not caused by a mechanical fault. he is positive that there is an electrical fault in my car.

 

Tech 2, Snap-on, OTC and many other scanners will show current misfires on each cylinder and misfire history for each cylinder... Cheaper to get it checked than just start throwing parts at it...

 

Sorry to hear you having so much trouble 8-(... My knowledge of C6 motor is nil but with P0300 is much.
Maybe go back to basics, on a cold engine running open-loop you really only need 3 things, air, fuel, and spark to get it to run...right.

Cuz it's such a modern setup you gotta trace all the wires, fuses, relays, etc.... to make sure you are getting proper fuel pressure, air, and amounts of fuel.

Air and Fuel are usually easier to check for so i would start there...you cleaned the injectors, are they firing at the proper time ? Plugs look fouled ? or lean ? or Okay ???

try not to through parts at it and get some tools and test parts are working (multi-meter to check ohms on injectors....)

Good Luck!
-ALF out....

 

you need to check compression. that will tell you if you have weak valve springs or possibly even a stretched timing chain, heaven forbid. cam sensor is a pain in the butt. can you see if there is any oil leaking from the front cover? that is where the cam sensor is.

 

did you perform the crank variation learn procedure?may be all it needs.service states this to be done before anything.your knock sensor error is picking up vibration and vibration is number 1 cause of your original code

 

Well honestly, where i live its very hard to find someone who knows all these steps and information. Luckly i found one. I asked him to fix the missfire issue and taking the vette to him tomorrow. Will update my post if the problem solved *fingerscrossed*

 

Yes the po300 is a misfire condition. The condition is sensed by the CAT TEMP heating from a lean condition If you already replaced the plugs and wires a vac leak can do it or a crappy connector maybe the ground on a fuel injector bank or a plug that services the ignition banks. Try pull a couple plugs apart.

 

SOLVED:

i picked up new set of spark plugs (Autolite 5245) and replaced the ones i just installed.

it turned out that the mechanic may have dropped the plugs before installing them or damaged them somehow.

another thing was the mechanic installed the rear O2 sensors in place of the front ones in the headers collector. so i picked up O2 sensor extension harness and installed them in the correct hole.

i scanned the car missfire is gone thank god but i have the O2 sensor thingy showing up which i will fix by taking the car to a programmer.


thanx guyz and hope my update helps anyone else facing P0300 code.

 

sometimes it takes some time to find the problem, good thing you are smart enough and don't have to pay someone to GUESS