QuestionHi, I just bought a couple of months ago the above car. Ever since I bought the car it has been misfiring and showing a check engine light. The dealer changed the spark plugs and coils on the driverside, did a fuel injection flush (they thought it was just bad fuel on the lines)and the car kept misfiring. I bought my own OBDII for codes, the last codes were P0300,P0301,P0306. I check all the vacuum hoses and replaced them ( they were breaking when touched). The P0300 and P0306 went away. Only the P0301 was showing, I changed the spark plug with one from autozone the NGK Iridium IX and clear the code. Engine light came back the next day and now I'm showing P0300, P0301, and P0302. Also the car jitters when in Parking. What do you think it could be? Should I buy the spark plugs from the dealer and change the coils from the passenger side? Do you think it could be the Ignition control Module?
AnswerHi Maria,
the reason the check engine light comes on is because the vehicle has picked up a fault with the emission system, i.e. the emissions have risen above the legal allowed maximum and the light is a way of warning you of this.
the codes you describe are as follows.
P0300-random multiple cylinder misfire detected.
P0301-cylinder 1 Misfire detected
P0302-cylinder 2 misfire detected
P0306-cylinder 6 misfire detected.
the cylinders are numbered starting from the front Left side when you are standing in front of the vehicle facing the engine. the first cylinder on the left closest to the radiator is cylinder one, the second one is cylinder two and the third one closest to the dash is cylinder three. then on the right side the closest one to the radiator is cylinder four and so on...
there are three main causes for misfires as follows:
Ignition-faulty spark plugs, faulty ignition coils,faulty camshaft position sensor, loose or dirty connections(especially on the plug leads) and some times moisture gets into the high voltage part of the ignition system causing short circuits which means the spark doesnt get to the plugs and cant ignite the fuel/air mixture.
Fuel-dirty injectors,low fuel pressure,fuel supply faulty(filter ad pump)
Compression-mainly caused by burnt valves(usually after the engine overheats but not right away) leaking head gasket or worn out piston rings.
other causes cqan also be:
leaking air intake system or even a stuck EGR valve!
to isolate the cause proceed as follows:
start with the ignition system. remove each spark plug and inspect it.(each plug has a story) do not mix them up so you know which cylinder is faulty.
a wet plug indicates a faulty spark, either the plug itself is faulty or the spark is shorting out to ground before it gets to the plug.(to see if there are any leaks in the plug leads start the vehicle in the dark and look for sparks(bright blue)
a plug that looks like its still new or lighter then the rest of the plugs indicates that no fuel is getting to the chamber, either a faulty injector or low fuel pressure(blocked fuel filter,faulty fuel pump or faulty fuel pressure regulator.)
also while the plugs are out have the compression tested(using a compression gauge) measure all the cylinders. they should be in the same range with a maximum permissible difference of 3 bar between them. big differences indicate a compression leak which can cause a misfire as that cylinder is 'dead'.
the ideal colour of the plugs after a few miles should be a light grey /beige some times with a red tan(caused by the additives in unleaded fuel.)
as for your other questions I doubt the ignition control module is faulty as if it fails then the vehicle usually does not start, how ever look at the connections where the plug leads enter, they should be clean with no signs of corrosion or moisture, white residue is normal, but not excessive.
and as long as you have put in good quality spark plugs then you should have no problem, unless you have been sold counterfeit products which shouldn't be the case if you have bought them from a reputable dealer.(in Kenya we have to be more careful as our consumer laws are not really up to date).
Also worth a check is the oxygen sensors, I have had a few cases where they cause fueling problems and there-by rough idling. Audi service recommended service interval is every 2 years, if the vehicle has been maintained by a dealer then there should be a record of oxygen sensor replacement in the service manual, (they are also called lambda probes)
and finally try this link out,
it gives descriptions of fault codes, their causes and also remedies.
http://wiki.ross-tech.com/index.php/Main_Page
hope this helps.
