Engine Troubleshooting FAQ

Quick Troubleshooting Topics With Answers

Engine Troubleshooting FAQ

Engine Troubleshooting FAQ
Engine Troubleshooting FAQ

Quick Troubleshooting Topics with Answers

Black smoke is coming from my exhaust.

  • This is an indication that too much gas is being burned. Your air/fuel mixture is too rich. You may have a clogged air filter. If the air filter is not clogged there may be a problem with a sensor controlling the vehicles fuel injection system. If your vehicle has a carburetor then the choke plate may be stuck. Another possibility is a vacuum leak.

White smoke is coming from my exhaust.

  • When a cold engine is started, any condensation that has formed in the exhaust will be burned off. This is normal and nothing to worry about. On the other hand if you see white smoke coming out of the exhaust at all engine temperatures then this is an indication of a blown head gasket or possibly a crack in the head, intake or cylinder. Basically what is happening is coolant is leaking into the cylinder and being burned off as steam.

Blue smoke is coming from my exhaust.

  • This is a definite indication that this engine is burning oil. The most common cause for this is bad rings and is most likely from high mileage. An engine with bad rings will also show signs of power loss, especially when going up hills. Another cause of blue smoke is bad valve stem seals. Usually the smoke is more noticeable during acceleration. Lastly if your vehicle has a turbo charger then it may possibly have leaking turbo charger seals.

Troubleshooting Why does your vehicle smells like rotten eggs.

  • The rotten egg smell is the result of unburned gasoline vapors reacting with chemicals in the catalytic converter. Your air/fuel mixture is too rich. You may have a clogged air filter. If the air filter is not clogged there may be a problem with a sensor controlling the vehicles fuel injection system. If your vehicle has a carburetor then the choke plate may be stuck or you may have a vacuum leak.

Your vehicle lacks power on flat roads as well as hills.

  • This usually indicates a problem in the ignition or fuel system or possibly a clogged catalytic converter. If the vehicle doesn’t seem to have the top speed it used to then suspect a clogged converter. If the engine runs roughly especially when idling it may be due to old/failing spark plugs and wires. Look for a fuel delivery problem in the carburetor or possibly a clogged fuel injector. Lastly, look for weak compression due to bad rings or valves possibly from high mileage.

What if your vehicle lacks power on hills but is fine on flat roads.

  • Pre-ignition:
    If you also notice a pinging noise then this would indicate a pre-ignition condition. Pre-Ignition means the air/fuel mixture in the engine’s combustion chambers is igniting earlier than it should. If you have been filling your tank with low octane fuel this could be the cause. Low octane fuel burns too easily and under certain conditions will self-ignite before the piston reaches the top of the combustion chamber.
  • Your engine makes its peak power when the ignition takes place while the piston is at the top of the combustion chamber, which is not the case with pre-ignition. Here you have pre-ignition and power loss. Try using a higher grade of fuel.
  • If your engine is running hot this could also trigger pre-ignition. During very hot days your engine will run hotter, this is normal and unavoidable. However if your engine is running hot when it shouldn’t, then you need to look into what’s causing abnormal engine overheating.
  • Thin air can also cause pre-ignition. If you are driving in high altitude areas try using a higher octane/grade of fuel. High octane fuels burn slower and are therefore resistant to preignition.
  • Rings or Valves:
    Weak compression due to bad rings or valves.

Troubleshooting Engine shakes while idling.

  • This is a telltale sign that the engine is misfiring on one or more cylinders. This may be as simple as spark plugs or spark plug wires but may also be a more serious internal engine problem like a burned valve.

Is your vehicle hesitating while accelerating.

  • If this happens only in the morning the culprit may be moisture in the distributor cap.

Why? During the night condensation or moisture can form on the inside of the distributor cap. This is due to cold and wet weather and the fact that the engine is cold. This moisture allows electrical current to arc inside the distributor cap and this arcing causes the engine to misfire.

  • If this problem has slowly gotten worse over time then a vacuum leak could be the cause.

Why? Vacuum leaks typically start out small almost unnoticeable and gradually become worse due to heat and pressure inside the engine. Any leak in a fuel system’s vacuum will intermittently throw off the air/fuel mixture that enters the engines combustion chamber. This results in a hesitation or sometimes, jerking.

  • If the hesitation has stayed the same over time then you may have a faulty accelerator pump on a carbureted engine.

Why? The accelerator pump gives the engine the extra fuel it needs to accelerate smoothly. A faulty accelerator pump will either not work at all or only work intermittently. In either case the result is usually hesitant or jerky acceleration.

  • If the hesitation has stayed the same over time then you may have a bad throttle position sensor on a fuel injected vehicle.

Why? The throttle position sensor measures how far the throttle is open and sends this information to the vehicles computer which in turn calculates the precise amount of fuel to inject into the engine. A faulty throttle position sensor will adversely affect the injection of gas into the engine, often resulting in hesitant or jerky operation.

Troubleshooting Engine stalls while accelerating.

  • If this happens only in the morning the culprit may be moisture in the distributor cap.

Why? During the night condensation or moisture can form on the inside of the distributor cap. This is due to cold and wet weather and the fact that the engine is cold. This moisture allows electrical current to arc inside the distributor cap and this arcing causes the engine to misfire. During acceleration this misfire gets so extreme it can cause the engine to stall.

  • If this problem has slowly gotten worse over time then a vacuum leak could be the cause.

Why? Vacuum leaks typically start out small almost unnoticeable and gradually become worse due to heat and pressure inside the engine. Any leak in a fuel system’s vacuum will intermittently throw off the air/fuel mixture that enters the engines combustion chamber. This results in a hesitation, jerking or in extreme situations, stalling.

Why would engine stall while idling: Fuel Injected System.

  • If the engine will stay running when you give it more throttle then you may have a faulty idle air bypass valve on a fuel injected engine.

Why? By giving the engine more gas when it is about to stall you are essentially compensating for a faulty idle air bypass valve by increasing the throttle thus giving the engine enough fuel to stay running.

  • If the stalling at idle only occurs when the engine is cold then you may have a problem with the cold start valve.

Why? This valve gives the engine more fuel for a richer air/fuel mixture that is needed when the engine is cold.

Why? The fuel pressure regulator maintains proper fuel pressure to the fuel injectors. Problems with this device will likely result in a fuel starved engine thus it will stall.

Troubleshooting Carbureted System: Engine stalls while idling.

  • If the engine will stay running when you give it more throttle then the idle speed may be set too low.

Why? By giving the engine more gas when it is about to stall you are essentially compensating for too low and idle by increasing the throttle thus giving the engine enough fuel to stay running.

  • If the stalling at idle only occurs when the engine is cold then you may have a problem with the choke.

Why? The choke restricts the amount of air going into the carburetor, thereby causing a richer air/fuel mixture that is needed when the engine is cold. If the choke is stuck in the open position then it will be creating a lean condition rather than the rich condition we need when an engine is cold and consequently stalling.

  • Another possibility is an obstruction in the fuel line or carburetor.

Why? An obstruction in the fuel line or carburetor would restrict the fuel flow to the engine resulting in stalling.

Troubleshooting Your oil light flickers.

  • Oil level may be low.-Check and refill to correct level.
  • Oil may be of wrong grade.- Check for correct grade of oil. Refer to handbook or bring vehicle in for inspection.
  • Oil sending unit may be defective.-Test sending unit and replace if faulty.
  • Oil pickup screen may be clogged.-Remove oil pan and replace or clean screen.
  • Crankshaft bearings or oil pump are worn.-This is a especially likely cause if the oil light only flickers when the vehicle is warmed up and idling in gear.

Troubleshooting When your heater blows cold air.

  • You may have a bad thermostat.

Why? The thermostat is a valve that opens and closes to regulate coolant flow through the engine. When the coolant is cold the valve will restrict coolant flow allowing the heat of the engine to increase coolant temperature. As the coolant temperature increases, the thermostat opens to increase coolant flow.

A thermostat has a heat rating that dictates how high the coolant temperature will be before it is fully open. A common thermostat will be 195 degrees F. First thing to do is to make sure that the coolant temperature is up to operating temperature, 195 degrees F or higher. A quick check by feeling the radiator hoses would tell you if it is hot. Using a thermometer taped to the upper hose of the radiator will tell you exactly where you are. If it isn’t hot enough, change the thermostat.

  • Your coolant level may be low.

Why? A low coolant level will reduce the flow to the heater core.

  • Your heater core may be clogged or restricted.

Why? If your heater core is restricted or clogged then coolant either isn’t flowing through it, or it is so slow that it is cooling down and that translates into your heater blowing cool or warm air inside the vehicle.

  • You may have a bad clutch fan, or fan switch.

Why? If you have a clutch fan it may be spinning too fast keeping the coolant temperature too low. If you have a electric fan it may be running too long or staying on, again keeping the coolant temperature too low.

You may have a blown head gasket.

Troubleshooting Your engine uses coolant but I don’t see any leaks.

Your intake gasket may be leaking. Why? The intake gaskets seal water that flows between the two sides of your engine. Many times when these gaskets loose their ability to seal it allows coolant to leak into your engines crankcase. Check your oil level. If the oil level is high and or if the color of the oil is milky or brown then you likely have coolant getting into your crankcase. Immediately have your mechanic inspect your engine. Do not drive or operate your vehicle with this condition as bearing failure will be likely. The coolant in the oil takes away the oils lubricating properties.

Troubleshooting Conclusion:

Troubleshooting is the most important part of auto repair. If you can properly troubleshoot a problem, you won’t waste time and money fixing things that don’t need to be fixed. If you can troubleshoot your bad engine performance, engine missing, misfiring, overheating, sounds like bad news, or other engine problems, you can repair them and be back on the road.

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