That is a random cylinder misfire. Most commonly that is spark-related, and that would send unburned fuel into the exhaust system. If this just started when the new spark plugs were installed, the obvious suggestion is to recheck the gap, but in a real lot of cases problems are caused by switching to the latest gimmick the spark plug manufacturers come up with to sell parts. "Iridium" and "split-fire" are two good examples of solutions where there were no problems. Those should only be used when specified by the vehicle manufacturer. Besides just providing a place for a spark to occur in the cylinder, the engineers have fine-tuned their emissions systems to even place the plugs' gaps in a specific orientation and angle within the cylinders. The wrong type of plug can place the spark in a spot where the fuel is harder to ignite or takes too long for the flame front to make its way to the outer edges of the cylinder. To add to the misery, your engine computer detects which cylinder is misfiring by observing where the crankshaft is when its rotational speed slows down very slightly due to the misfire. We normally feel that misfire because the heavy mass of the crankshaft slows down, then speeds back up, but if the burn is simply incomplete, we may not feel the misfire even though the computer detects it.
When a random misfire becomes a problem and no service was done recently, fuel is the better suspect since that is the only thing all the cylinders have in common. Chrysler has almost no trouble with low fuel pressure, but fuel quality must be considered. If the vehicle's tank was filled right after the tanker truck refilled the tanks at the gas station, debris and water will have been stirred up. That water can make its way into your gas tank. The ethanol found in most gas today can absorb some of that water to get it through the system, but that water still is not going to develop any power in the engine just because it made it that far. In this case, the fuel could be just on the edge of burning completely or not developing full power. The engine may run poorly with too much water in the gas, but the engine computer can detect that long before it gets bad enough for you to feel it.
Wednesday, March 7th, 2018 AT 5:07 PM