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Posted on Jan 02, 2017
I would start with a test drive with a fuel pressure gauge on it make sure you have spec. 35 - 40 psi. Clear codes and record all the freeze frame data in obd2 as you will need this in the diag process. 442 and 456 are evap codes I believe, do they return with the 300 misfire codes? Either way you need to reproduce the problem with the gauge on it and get the first code it sets. Could be fuel pump/filter/sending unit assy. In this case you will need to pay attention to the fuel level when this occurs. (same level as before)
Posted on Nov 24, 2008
Main causes of misfire would be loss of spark; the air/fuel mixture is too far out of balance to ignite; or loss of compression.
Loss of spark includes anything that prevents coil voltage from jumping the electrode gap at the end of the spark plug. Causes include worn, fouled or damaged spark plugs, bad wires or even a cracked distributor cap. A weak coil or excessive rotor gas inside a distributor would affect all cylinders, not just a single cylinder.
"Lean misfire" can occur when the air/fuel mixture is too lean (not enough gasoline in the mixture) to burn. This can be caused by a dirty, clogged or inoperative fuel injector; air leaks; or low fuel pressure because of a weak pump, restricted filter or leaky pressure regulator.
Loss of compression means the cylinder loses most of its air/fuel mixture before it can be ignited. The most likely causes here are a leaky (burned) exhaust valve or a blown head gasket. If two adjacent cylinders are misfiring, it's likely the head gasket between them has failed. Also, if an engine is overheating or losing coolant, it's likely the head gasket is the culprit.
You can isolate the weak cylinder by temporarily disconnecting each of the spark plug wires, one at a time, while the engine is idling. When there's no change in the idle speed, then you have pinpointed the weak cylinder.
Posted on Aug 25, 2009
dear friend:if the vehicle seems ok then just remove the battery cable for a few minits,reconnect and see if faults is cleared,if not take it to a dealership to read the codes
Posted on Sep 23, 2009
I have changed plugs using the platinum plugs and the problem don't go away. These plugs can make a car run worse in some cases. I have found it best to use the OEM or a step above on 4 cylin and 6 cylin engines. The Plats work fine in 8 cylin engines. You could also have a bad plug wire. The plug wire could be jumping spark. At night, open the hood, start the car with lights off. Look around the plug wires for sparks jumping. If a wire is bad, the spark is leaving the wire and grounding itself to the nearest metal causing rough engine idle and misfire.
Posted on Jun 16, 2010
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