Join Date: Jan 2009
Location: San Antonio (moved back home)
Thanked 112 Times in 87 Posts
Feedback Score: 0 reviews
A short drive to the dealer should be ok... otherwise you don't want excessive unburnt fuel to burn up the cat on that cylinder bank.
More info -
Common Causes for an Engine Misfire and Code P0304
An Ignition System problem is one of the most common reasons for an engine to misfire. As the spark plugs, ignition cables, distributor cap and rotor, and ignition coil wear over time, their ability to transfer the needed spark to ignite the air/fuel mixture inside the combustion chambers becomes compromised. In the early stages, the spark will only be weaker and the actual misfire will be subtle. As the ignition components continue to wear, the misfire will intensify and the combustion process can be interrupted completely. This will cause a severe jerk or shock in the operation of the engine (the engine may even backfire through the air intake system, producing a loud "pop").
Carefully inspect all of the Ignition System components for wear and heat damage. The Spark Plug terminals should have a sandy color and not be blackened with soot, white from an overheating combustion chamber, or greenish from coolant. Neither the Ignition Cables nor the Coil(s) should have any signs of arcing. If possible, Scope Check the Ignition System to ensure that the firing voltages are even—about 8 to 10 kilovolts per cylinder. If there is a Distributor on the engine, remove the Distributor Cap and Rotor. Inspect their terminals and contact points for wear, signs of arcing, and/or any buildup from corrosion. Though all ODB II vehicles have computer controlled timing, be sure to verify that it is within spec, even if it uses individual coils.
The lean misfire is another common reason for an engine "miss"—this is due to an imbalanced air/fuel ratio (too much air/too little fuel). Since an engine needs a richer (more fuel) mixture for a smooth idle, this problem may be more noticeable when the vehicle is idling. The lean misfire may decrease or disappear as the engine speed increases because the efficiency of the volumetric flow into the combustion chambers increases dramatically. This is one reason why a vehicle gets better mileage on the freeway than in the city. An EGR valve that is stuck open, a leaking Intake Manifold Gasket, a defective Mass Air Flow Sensor, a weak or failing fuel pump, or a plugged fuel filter are some of the many causes for a lean misfire.
Pay very close attention to the Long Term Fuel Trim values because they indicate how much the Powertrain Computer is compensating for an imbalanced air/fuel ratio. If the Long Term Fuel Trim is over 10 percent on one bank of cylinders and not the other, there might be a vacuum leak or defective/cracked intake manifold on that specific bank. It is important to determine what is causing this amount of compensation. Check the Fuel Trim "numbers" over the full range of operating conditions. A healthy engine should have Long Term Fuel Trim numbers around 1 to 3 percent, either positive or negative.
Mechanical problems can also cause an engine to misfire. Common causes of a mechanical misfire are worn piston rings, valves, cylinder walls, or lobes on a camshaft; a leaking head gasket or intake manifold gasket; damaged or broken rocker arms; defective fuel injectors (and/or the electronics that control them); and a slipped or incorrectly-installed timing belt or timing chain. Generally, this type of misfire has more of a "thumping" feel to it. It is usually noticeable regardless of engine speed; in fact, it may even intensify as the engine speed increases.
A Compression Test and an engine idle Manifold Vacuum Test are two very important methods of determining the mechanical condition of the engine. Compression readings that are consistent (within 10 percent of each other), and at least 120 PSI per cylinder and a minimum of seventeen inches of steady vacuum, are required for reasonably smooth and complete combustion.
Sometimes, the engine has nothing to do with a misfire. One common cause for "jerky" performance that feels like a misfire is a problem in the transmission and its ability to properly up- or down-shift. If the misfire occurs during higher speeds, it could be a problem with the operation of the overdrive gear or a chattering clutch in the Lockup Torque Converter. If the vehicle jerks or feels like it is "missing" during deceleration, it could be due to harsh transmission downshifts, badly warped rotors, out of round brake drums, and/or sticking brake pads or brake shoes.
Vehicles can set misfire codes when badly warped and out of round rear brake drums violently jerk the entire powertrain when the vehicle slows from highway speeds. Make sure that you have the vehicle properly inspected in order to determine the root cause of the misfire. Entire engines have been replaced to solve a wrongly perceived mechanical misfire problem that was actually rooted in the transfer case, transmission, driveshaft, or front/rear differential.
2009 R/T Challenger
Bought on Dec 26, 2008