Weak sparks are orange or red and may be hard to see in daylight. If you did not see a spark, remove the coil wire from the distributor cap. Attach the spark tester to the distributor end of the coil wire. Crack the engine and check for a good spark at the spark tester.
Blisters on the insulator tip, melted electrodes, or white deposits are signs of a burned spark plug that is running too hot. Causes can include the engine overheating, incorrect spark plug heat range, a loose spark plug, incorrect ignition timing or too lean of an air/fuel mixture. The spark plug should be replaced.
The strength of the spark is revealed in the color. A red or yellow spark is weak and probably will not spark in the cylinder. A blue or white spark is strong and has enough voltage to fight across the spark plug gap even under pressure within the cylinder.
Black, chunky carbon buildup spanning the gap between the sparking end of the plug and the hook-shaped metal piece overhanging the end. Dark carbon residue built up on the ends but not spanning the gap. Oily residue on the end (most likely to happen with two-stroke engines that use a gas/oil mixture).
Loss of spark is caused by anything that prevents coil voltage from jumping the electrode gap at the end of the spark plug. This includes worn, fouled or damaged spark plugs, bad plug wires or a cracked distributor cap.
A good spark will be blue-white and will be plainly visible in daylight. If a good spark is present, the problem is probably not in the ignition system. Check the fuel system and/or stark timing. Weak sparks are orange or red and may be hard to see in daylight.
The most common signs of bad spark plugs include start-up trouble, rough idling, sluggish acceleration, declining fuel economy, engine misfiring, and engine knocking.
A weak spark is the first sign that the ignition coil may be failing. During acceleration, the air and fuel that is forced into the cylinders extinguish whatever spark there is, which causes the car to stall.
Intermittent misfires are almost always caused by a weak spark or a lean fuel mixture. That piece of knowledge may not tell you what exactly is causing the misfire, but it should lead you toward a coil problem or an injector problem. Random misfires are another type of misfire that can be very difficult to diagnose.
A spark-ignition engine is an internal combustion engine, generally a petrol engine, where the combustion process of the air-fuel mixture is ignited by y a spark from a spark plug. A bright blue spark is best. A yellow/orange spark signifies weak ignition. The hottest spark is ultraviolet which we can't see.
Black exhaust smoke
“When your exhaust pipe gives off black smoke, one of the things to get worried about are bad or worn out spark plugs. It means fuel burning in the combustion chamber is not being done 100 percent or burnt fully. It also means that air is not being well mixed with fuel to burn effectively.
The Spark-Plug Gap
If the gap is too small, the spark will likely be too weak and cause the engine to run poorly or with poor efficiency.
Visual Inspection. Remove and compare your old spark plugs to a new one. If the tip and/or electrode show excessive wear they should be replaced. Also, look for fuel and oil contamination.
A fouled or bad spark plug is a plug that has become covered with a substance like oil, fuel or carbon or one that is blistered from running too hot. Driving with fouled or bad spark plugs can cause a host of problems for your engine.
If there's too much air in the cylinders at the time of the spark, and not enough fuel, the spark won't be able to ignite all the fuel at once. Yet again, leftover fuel vapor will flow into the exhaust and could combust there in a backfire.
A weak or damaged ignition coil can cause engine misfires, stalling, poor performance, and lower fuel economy. A completely faulty ignition coil can often keep the vehicle, especially a 4 cylinder vehicle, from running at all.
The least likely cause of a weak spark is a battery voltage of 12.2 Volts. Even though the battery voltage is less than normal, it should be enough to allow the ignition coil (s) to become fully saturated and provide the correct spark to the spark plugs.
If your engine misfires or stalls when you are idle or when you stop suddenly or accelerate, there could be a problem with your ignition coil. A misfire — which can sound like a coughing or sputtering noise or feel like a jerk or strong vibration — means that one of the engine's cylinders is not firing correctly.
Bad Sparks
While a brief, odorless spark shouldn't worry you, it's time to contact an electrician if you see a spark that has one or more of these characteristics: It lingers and fizzles, as opposed to briefly flashing. It's noticeably white or yellow, as opposed to blue.
When To Replace Spark Plugs Quick Tips. Your owner's manual recommends when to replace spark plugs. Some require changing at 18,000 miles, some at 35,000 miles, and others at 100,000 miles. Reduced acceleration, engine misfires, and rough idling are symptoms indicating you might need new spark plugs.