Wednesday, April 30, 2014
Can You Pull off Spark Plug Wires While the Engine Is Running
Like most ponderings in automotive repair, the question of removing spark plug wires from a running engine isnt necessarily so much one of "could" as it is of "should." Technically, yes, you can yank the plug wires off of a running engine just as easily as you could one that isnt running, but it may not necessarily prove conducive to you or your cars good health.
You Could
Removing a plug wire from a running engine isnt likely to result in catastrophic engine failure, particularly if you put it back on shortly afterward. All spark plugs misfire from time to time, you just dont notice it because its intermittent, random and usually happens so quickly that the cylinders firing again before the engine has a chance to vibrate. So, intentionally creating a misfire by removing the plug wire for a few seconds or even a few minutes isnt likely to destroy anything on most engines.
Common Effects on the Engine
Most engines have a rubber ring on the front of the crankshaft called a harmonic balancer; on the outer edge of the balancer is a heavy, metal ring. When the explosions in the engines cylinders push down on the pistons, the forces they exert quickly accelerate the crankshaft. When that accelerations over, the crank tries to slow down, resulting in a constant cycle of acceleration and deceleration that manifests as vibration in the crankshaft. The metal ring on the balancer resists these sudden, but tiny, vibrations and keep the crank from tearing itself in two. Over a long enough period of time, a dead cylinder and the resultant heavy vibration will over-work the balancer, causing it to fail. Once that happens, you could be looking at serious damage to the engine.
Effects on the Converter
Your cars catalytic converter works something like a blast furnace to convert toxic gases produced by your engine into more inert forms that wont drown polar bears or grow fish with three eyes. The converter takes advantage of unburned fuel -- which is, itself, a pollutant -- coming from your engine and uses it to fuel the furnace in the converter matrix. More fuel means more heat. Killing the spark in one cylinder will drastically increase the amount of fuel pouring into your exhaust, which will, at some point, cause the converter to overheat and fail. The engines control computer will compensate for this to some extent, but you can count on extra fuel going into the exhaust.
Lean-Out
Depending upon the computers control strategy, disconnecting a plug wire and leaving it that way could seriously fry something. When the oxygen sensor detects excess fuel in the exhaust, your cars computer may assume that this represents a net excess of fuel through all the cylinders. It will respond by decreasing the amount of fuel injected to all of the other cylinders in order to get the air/fuel ratio back in line. The resulting lean condition will increase combustion chamber temperature, causing overheating, detonation in the engine and, eventually, complete meltdown. Most computers do have programming provisions to account for a dead cylinder, and wont react this way; but some dont, and theres no way to be sure unless you know exactly how your fuel injection system thinks.
Safety Issues
Before pulling the plug wire off of a running engine, bear in mind that your are, in fact, grabbing a live wire with about 40,000 volts worth of electricity coursing through it. Normally, this electricity will pass through the plug wire and race to the spark plug, which acts as a ground. But when you remove that ground, the spark is going to find the next, most convenient ground. If you happen to be touching the body of the car when you pull the wire off, then you become that ground. While electricity normally wouldnt arc through the insulation, even if it is a bit old and damaged, removing the primary ground will make that spark pretty determined to get out whatever way it can. Its not likely to kill you unless you have heart or nervous system problems, since the amperage is very low -- but the sensation is rather, shall we say, "life affirming."
No comments:
Post a Comment