Question about GMC C1500
P0300 = random misfire
most common problems are O2 sensor bad, intake manifold leaking, or catalytic converter plugged up
check your o2 data see if one side is reading lean or rich. make sure your short term fuel trim is ok.
if your o2 sensor is not reading normally replace the sensor.
look at your misfire data. if its one whole bank its probably a intake leak.
see them alot with o2 sensor problems and catalytic converter problems. if its not those 2 things then its an intake manifold.
basically thats the 3 things that fail on that vehicle, very common also there is a bulletin for a bad PCM ground. located at the front of the engine on some vehicles or on the back side. right bank. its a ground strap that attaches to the block. it can also cause an intermittent misfire problem
Posted on Mar 18, 2011
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Posted on Jan 02, 2017
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Sep 03, 2016 | Cars & Trucks
Inspect the EIS towers and plug the wire connections for corrosion or other signs of poor retention at connections.
The electronic ignition (EI) module supplies a signal to the PCM whenever it determines that the #4 cylinder fired on its compression stroke. Because of opposite coil tower polarity, the simultaneous fir of #1 and #4 cylinders are of opposite polarity as well. Under most conditions, except decel, the waste spark cylinder fires before the compression cylinder in sequence. The EI module can determine this polarity sequence and voltage amplitude by using capacitive pickup plates located under the 1/4 coil. If the module senses a positive to negative sequence and high negative spike when #4 is on TDC, it pulls the PCM cam signal to ground signaling that #4 has just fired on compression. This signal along with the double pulse received from the CKP sensor, synchronizes spark and fuel timing.
Beside plugs , plug wires need to be replaced as well !
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