Last night on the way home from work I starting noticing a misfire, then my CEL appeared. Ran the code reader and got a P0303. Stopped by the parts store and picked up a Champion plug, then proceed home (no tools in the truck).
Got home and the parts store gave me the wrong plug. So I checked the gap (which was larger than 0.040).
My thought was to test the plug (in case the coil had gone bad). So I put the problematic plug (after i re-gapped) and put it in the #1 position.
Cleared the code, re-started the truck and then I got a P0300
Got the correct plug and replaced the suspected fouled plug. Cleared the code and restarted.
No codes, but the truck still misfires.
Wont rev above 4000 while in park.
My volt meter is at work, so I cannot test my battery tonight. But this is what I think might be going bad???
Plugs,coils, and O2 sensors were replaced less than 1 year ago.
Battery is 4+ years old.
Is there anything else to look for?
Thanks in advance for any input.
*Bad plug <-----you already debunked
*Bad Coil Wiring
*Bad injector Wiring
*Improper Fuel Pressure <----check static and operating PSI
*Compression in Cylinder 3 <---good idea to check all cylinders
Im sure there might be a few more, but this is what pops into my head. All of these should be checked......remember you need compression, spark and fuel to create BANG
Battery checked out okay. Tomorrow I will replace all plugs and go from there.
I find it strange I am still not getting a code with the obvious misfire.
Most newer vehicles are rev limited by the engine controller while not in drive. Another possibility is that you have a cat starting to go out on you. you can test by removing the o2 sensor on the side you suspect and tie it off somewhere safe while still plugged in and go for a drive. If you see improvement, then the cat on that side is going. Found this thru experience.
.........OR just use a IR Thermometer to test the input and output temps. The outlet should be 100* hotter than the inlet after running @ 2500 RPMs for 5 minutes. If not then you have a bad cat.
What namresud described is an incorrect way to test and will cause the vehicle to stay in Closed Loop operation (not good)
P0300 Diagnostic Code - Random Misfire
Random/Multiple Cylinder Misfire Detected
What does that mean?
Basically this means that the the car'shttp://images.intellitxt.com/ast/adTypes/icon1.png 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:
A code P0300 may mean that one or more of the following has happened:
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 cathttp://images.intellitxt.com/ast/adTypes/icon1.png 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 vacuumhttp://images.intellitxt.com/ast/adTypes/icon1.png leak in the intake manifold or unmetered air getting past the airflow sensor, or an EGR valve that is stuck open.
Other P0300 Reading
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