Mis fire cylinder
Cylinder misfires come in many different flavors. Sometimes only 1 cylinder will fail, sometimes more, and sometimes it will jump around. The lesser amount of cylinders you have, the more noticeable the misfire will be. In all cases it depends on the condition of the electronics, and hardware (i.e.; spark plugs, spark plug wires, coil/coil pack(s), etc.) In my experience, the lesser amount of electronics you have, the easier solving the problem will be. This answer applies only to gas powered internal combustion engines. Not diesel powered engines.
First you want to make sure that ALL hoses and electrical connectors/wires are located in their correct place, and connected properly. Next to identify the problem. When does it miss? At idle or throughout the driving range (while at idle and in motion). Is it intermittent (does the miss occur randomly)? Does the vehicle seem to have 1 miss? Or more than one miss (This is more easily noted on vehicles equipped with motors that contain a smaller amount of cylinders)?
Now to explore each question, I will use a hypothetical situation. I have a small car with a 4 cylinder motor. I drove it home last night, and when I started it this morning, it had a definite miss.
To identify which of the cylinder(s) are misfiring, no actual tools are required. To find which cylinder(s) are having the problem, simply open the hood with the key "off," and check to see if anything is loose (i.e. a spark plug wire). If everything is snug, try removing one of the plug wires (NOTE: Only remove 1 plug wire at a time!). Then reach inside the car and try to start it. If you have a 4 cylinder motor any difference will become immediately apparent. In fact, most times the car will fail to start and stay running. If the plug wire you removed made no difference in the way the car runs, that means that cylinder is not firing. Replace the wire to its original location, and make sure that it is snug. Try another wire. Continue this process until you find the cylinder(s) that are causing the problem. (NOTE: Keep notes on which cylinder(s) are having the problem, and how the car behaves.)
Once you have identified which cylinders are having the problem, it is now time to determine the source of the problem. On newer cars (approx. 1985-present, depending on make and model) the problem can be more complex to try and solve. In this scenario, I am using an older car. Now it is time to see if the spark plug is getting any spark. To test this, remove the spark plug wire from the bad cylinder's spark plug, and set it against something metal on the motor, for best results, place the metal tip of the wire slighty away from the metal object (like the valve cover), but close enough for the spark to arc across (approx. 1/4 inch is best). Start the car. If you look at the tip of the wire and there is a spark arcing across the wire to the motor, that wire is transmitting spark. If it does not, skip down to the next paragraph. Since the wire is transmitting spark, the next thing to check would be the spark plug. (At this point you will need tools) Remove the sparkplug from the misfiring cylinder, and check for detonation of the tip of the plug (plug tip is destroyed), corrosion(white chalky residue), and foulage (if the plug is wet, and it smells like gas, that means that there is fuel getting to the plug, but the plug is not igniting it. If the residue is oily, then there is oil seeping in through to the combustion chamber. If it is not oily or wet, but is black, that means that the plug is carbon fouled, either from too much fuel (a rich fuel mixture), or that the spark plugs have not been cleaned/ replaced in a long time. To test the spark plug, plug it back into its wire, and set it again against something metal (NOTE: Make sure the location yout choose, has the least chance of falling over and into other moving parts). Start the car, and check for spark at the end of the plug, if there is no spark, the plug is dead, and needs to be replaced. If it does spark, that means that there is either a fuel delivery problem, sensor malfunction, or vacuum/vacuum hose leak, and not a spark issue
Nov 06, 2009 |
1996 Ford Taurus