There was no seal between the cap and distributor, and some fresh air was also drawn in from this area and ozone was pushed out. When fresh air flows through the distributor it is also a dryer to help reduce the accumulation of moisture. But the greatest amount of moisture gathering does not occur while the engine is running; it happens through condensation after the engine is shut down.
When the engine stops running, the rotor stops drawing fresh air through the distributor. The ambient, or outside air, will cool at a faster rate than the warm air inside the distributor. When the distributor’s ventilation is restricted, the warm air inside the distributor cap will cool very slowly, and because of the temperature difference to the ambient air, condensation will form on the inside of the cap.
In cooler climates, this rate of condensation is greatly amplified. Through convective heat transfer, proper distributor ventilation allows the warm air to move out from inside the distributor and draw the cooler ambient air in, equalizing the temperature change and greatly dropping the possibility of any condensation.
After a close inspection of the distributor cap, we noticed carbon traces leading from the brush area to cylinder number four. Cylinder four is the closest conductor to the carbon brush. Due to the design of this cap, the easiest path is through the number-four-cylinder-conductor inside the cap. Whenever you notice carbon tracking it is critical to check the ignition wires and spark plugs for wear.
We removed the screens and cleared the ventilation ports on the distributor, replaced the cap, rotor, ignition wires, and spark plugs and cleared the code. We took it for a test drive and it was running smooth, and the P0300 code didn’t return.
Remember, when a P0300 misfire code sets it could be an ignition, fuel, or mechanical issue. The first step in the diagnosis is to determine which system has the problem.
This entry was submitted by Mark Hicks and edited by Lauren Muskett.
Mark Hicks is an ASE Master and L1 certified. He is an independent shop owner of 15 years, and he has spent 21 years working for Wells Vehicle Electronics as a technical services manager.
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