Keep getting a #6 cylender misfire and lean code all checks ok has new plugs and coil packs. new fuel filter. usually happens after rain, cleared up last summer. new plug wires too

My 96 century with a 3.1 v-6 gave me fits for years shooting a 171 code(running too lean) I wound up changing the fuel filter and the problem went away. If it's been a while since the filter was changed, try it.

it sounds like low fuel pressure. Change fuel filter first then fuel pump if that fails. Misfire could be a coil pack and may not be related.

Hi there:
DTC P0300 - Random/Multiple Cylinder Misfire Detected



There are many issues that could cause this concern. Most common would be spark plugs and wires. A bad coil will also cause this issue. If this is the only code stored, it may be just that easy.


Other causes could be the engine is running lean, such as a vacuum leak in the intake. Also low fuel pressure or a injector that is dirty or going bad. A clogged catalytic converter may also cause a mis-fire condition.

A code P0300 may mean that one or more of the following has happened:

• Faulty spark plugs or wires
• Faulty coil (pack)
• Faulty oxygen sensor(s)
• Faulty fuel injector(s)
• Burned exhaust valve
• Faulty catalytic converter(s)
• Stuck/blocked EGR valve / passages
• Faulty camshaft position sensor
• Defective computer

Additionally, I would check all vacuum lines it is very common on this vehicle for there to be a vacuum leak, if none are found I would get the fuel injection system cleaned it is often the cause of a misfire.
Hope this helps; also keep in mind that your feedback is important and I`ll appreciate your time and consideration if you leave some testimonial comment about this answer.

Thank you for using FixYa, have a nice day

usually this code is followed by another number 1-4 or 1-6 or 1-8 depending on how many cylinders your vehicle has ,, what the code you got is a basic P0300 Random/Multiple Cylinder Misfire Detected A code P0300 may mean that one or more of the following has happened:

• Faulty spark plugs or wires
• Faulty coil (pack)
• Faulty oxygen sensor(s)
• Faulty fuel injector(s)
• Burned exhaust valve
• Faulty catalytic converter(s)
• Stuck/blocked EGR valve / passages
• Faulty camshaft position sensor
• Defective computer
• I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.
  Random misfires that jump around from one cylinder to another (read: P030x codes) also will set a P0300 code. The underlying cause is often a lean fuel condition, which may be due to a vacuum leak in the intake manifold or unmetered air getting past the airflow sensor, or an EGR valve that is stuck ope
  

CODE PO300 MULTIPLE ENGINE MISFIRE DETECTED CONDITIONS, MISFIRE CONDITIONS COULD BE LEAN MISFIRE,CAUSED BY WEAK FUEL PUMP FUEL PRESSURE SHOULD BE 50 - 60 PSI WITH NEW FUEL FILTER.CLEAN FUEL INJECTORS BY ADDING A BOTTLE OF SEAFOAM TO 3/4 TO A FULL TANK OF GAS.SEE WHAT HAPPENS.

P0300 - Random/Multiple Cylinder Misfire Detected

Basically this means that the the car's computer has detected that not all of the engine's cylinders are firing properly.

A P0300 diagnostic code indicates a random or multiple misfire. If the last digit is a number other than zero, it corresponds to the cylinder number that is misfiring. A P0302 code, for example, would tell you cylinder number two is misfiring. Unfortunately, a P0300 doesn't tell you specifically which cylinder(s) is/are mis-firing, nor why.

Symptoms may include:
* the engine may be harder to start
* the engine may stumble / stumble, and/or hesitate
* other symptoms may also be present

Causes: A code P0300 may mean that one or more of the following has happened:
* Faulty spark plugs or wires
* Faulty coil (pack)
* Faulty oxygen sensor(s)
* Faulty fuel injector(s)
* Burned exhaust valve
* Faulty catalytic converter(s)
* Stuck/blocked EGR valve / passages
* Faulty camshaft position sensor
* Defective computer

Possible Solutions:
- If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.
- If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.

Random misfires that jump around from one cylinder to another (read: P030x codes) also will set a P0300 code. The underlying cause is often a lean fuel condition, which may be due to a vacuum leak in the intake manifold or unmetered air getting past the airflow sensor, or an EGR valve that is stuck open.

Keep us updated and remember to rate this answer.

P0171------ system too lean bank#1
Po174------ system too lean bank#2
For these 2 codes, try cleaning the maf sensor (mass air flow), that is mounted in the big black hose that goes from the air filter housing to the throttle plate, if it is dirty, that will cause those 02 sensors to send a signal to the computor to lean the air fuel mixture. If cleaning it doesn't work, the sensors will probably need changing.
P0300---- Random/multiple cylinder misfire
P0316---- Cylinder misfire at start up---- first 100 revolutions.
On those 2 codes, you have to do some testing to find out why there is a misfire.
Possible causes:
dirty/malfunctioning injectors
weak coil pack
fowling spark plugs/wires
Low fuel pressure

P0304 Code - Cylinder #4 Misfire Technical Description Cylinder #4 Misfire Detected
What does that mean? A P0304 code means that the the car's computer has detected that one of the engine's cylinders is not firing properly. In this case it's cylinder #4.
FB.init("dd7d9e9681341cde77587bc6a2029f6f"); OBD-Codes.com on Facebook SymptomsSymptoms may include:

• the engine may be harder to start
• the engine may stumble / stumble, and/or hesitate
• other symptoms may also be present

Causes A code P0304 may mean that one or more of the following has happened:

• Faulty spark plug or wire
• Faulty coil (pack)
• Faulty oxygen sensor(s)
• Faulty fuel injector
• Burned exhaust valve
• Faulty catalytic converter(s)
• Running out of fuel
• Poor compression
• Defective computer

Possible Solutions If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.
If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors
.

A multi misfire may mean that one or more of the following has happened:
Faulty spark plug or wires, Faulty coil (pack), Faulty oxygen sensor(s), Faulty fuel injector(s), Stuck/blocked EGR valve / passages, Faulty camshaft position sensor, Defective computer.

The engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wire, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the the problems were faulty fuel injectors. 

Random misfires that jump around from one cylinder to another (read: P030x codes) also will set a P0300 code. The underlying cause is often a lean fuel condition, which may be due to a vacuum leak in the intake manifold or unmetered air getting past the airflow sensor, or an EGR valve that is stuck open.

Good luck and hope this information helps, keep me posted, be glad to help you get the truck running 100% again. Not sure if your running a K&N air filter, and if you are there may be a flim of oil on the MAF sensor that is making you run lean. You may want to spray down the MAF sensor with a can of MAF cleaner. 

Sounds like two problems. P0300 and P0303 are possibly spark plugs. They could be a coil pack but I'm leaning toward a spark plug problem because of the other two codes - they're indicating O2 sensor problems. If the O2 sensors are screwed up, the car reverts to preprogrammed, rich fuel maps that send excessive fuel through the engine. The reasoning is, if the ECU can't trust the O2 sensors to determine how much fuel to burn optimally, it'll pump a bunch of extra fuel through the engine to keep it safe. Having too little fuel (aka running lean) can destroy an engine, so the ECU plays it safe and runs rich (too much fuel) instead. The consequences of rich running are relatively minor compared to lean running, but can and do tend to create excessive carbon buildup on the catalytic converter and O2 sensors, as well as fouling spark plugs.

First thing to do though is to swap the wires on your coil packs and see if you end up with a misfire code for the same cylinder #3. If you do, then it's the plug or wire. If it moves, it's the coilpack. Replace whichever part is faulty. You'll probably need oxygen sensors too, before you can clear all the codes.