Engine Running Rough At Idle, What's The Solution?

Troubleshooting Engine Running Rough

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Troubleshooting for Engine Rough at Idle

What exactly the word ‘rough’ means? So far as engines are concerned the rough running of engines owe to lop-sided power output. Rough running must not be confused with vibrations. Because in vibration the frequency and amplitude of running engine remains uniform/constant. Rough running of an engine owes number of factors, so it is essential for troubleshooting to take account of factors save vibrations. Factors that contribute to rough running are following. CITATION Bus13 \l 1033 (Busch, 2013)

High Power Settings

first of all, high power settings need to be checked. Power loss, if any, needs to be examined. Engine running following the pull of throttle must be noted. If the initial diagnosis confirm that aforementioned factors are responsible then the inspection has to start from ignition system.

Following the inspection of high-power settings roughness has to be defined precisely. The roughness could be brief, incessant, severe but brief, sudden vibration, roughness at low power. All these factors can be looked upon to inspect the running engine roughness. Our concern is actually th roughness at low power or Idle. Following is the troubleshooting of engine roughness at low power or idle. CITATION Son15 \l 1033 (Englert, 2015)

Engine Running Roughness at Idle

The first step in the inspection would be to check the roughness at the specific throttle movement. If the roughness is witnessed at the first third throttle movement and following that engine running is smooth at full throttle then the engine would most likely have an ‘induction system leak’. If the throttle is closed and the pressure in the induction system, which is downstream of the throttle valve is lower than the atmospheric pressure. This is because a defective gasket, fractured hose or abraded tubing will allow engine to take extra air into the intake. The extra air doesn’t mix with the fuel and consequently the mixture gets propped. Extra air is most likely to enter the induction system through a primer system.CITATION Lyc \l 1033 (Lycoming Engines, 2005)

If the boost pumps of the engine are on at idle and the engine is still running rough, giving away black smoke then it would be concluded that the idle mixture is too rich and/or the pressure in the boost pump is high. The best troubleshooting in such a condition would be to lean the idle mixture at injector or to lower the boost pump pressure. The engine is fuel injected and might have a stabbing valve in the flow driver owing to debris, then it has to cleaned to solve the issue.

There is a possibility that spark plugs have become contaminated if the engine, on low rpm and rich mixture, for extended time on the ground. The ignition check following that will reveal rpm drops. The engine may stumble as well if such condition prevails for long.

The best way to troubleshoot such a problem is to lean the air, fuel mixture, increase the power and then wait until the deposits burn off completely. Following the smooth running if ignition shows minor difference and drop in rpm then the aircraft is all set to get airborne. One thing which has to be kept in mind,there would still be deposits on the spark plugs which can be burnt off by the high engine temperatures.CITATION Lyc1 \l 1033 (Lycoming, 2006)

Uneven fuel pressure, if the engine is fuel injected, also leads towards the rough running at low power or idle. The exhaust valves may be burnt or their springs may be broken. In such a case rough running will be persistent. If the push rod is bent owing to sticking valve, then it will not the valve to open properly anymore and the result would be continuous rough operations at idle.

Reference

BIBLIOGRAPHY Busch, M. (2013). Rough Engine. Sport Aviation, 34.

Englert, S. (2015). Piston Engine Troubleshooting for Pilots.

Lycoming Engines. (n.d.). Lycomings Operational Manual. Lycomings Engines.

Lycoming. (n.d.). Troubleshooting Guide. Williamsport, PA.