Engine Troubleshooting FAQ – Automotive Repair Help With Solutions

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This page provides answers to some of the most frequently asked questions about and service.

In comparison to wrenching, requires a more in-depth knowledge of the workings of an .

But,  It takes a higher level of study to be able to accurately determine which part needs to be changed.


Engine Troubleshooting – Smoke

Tailpipe Smoke
Tailpipe Smoke

Black smoke is coming from my exhaust.

  • Most of the time excessive fuel is being burnt. 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. 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 turbocharger seals.

Why does your vehicle smells like rotten eggs.

  • The rotten egg smell is the result of unburned fuel vapours 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. 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.

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

Premature Combustion
Premature Combustion
  • 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.
  • Your engine makes its peak power when the plug fires while the piston is at the top of the cylinder. 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 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.

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.


Engine Troubleshooting – 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. Consequently, 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.

  • A vacuum leak could be the cause if this problem has slowly gotten worse over time.

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 systems 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.

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.

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


Engine troubleshooting –  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 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.

  • A vacuum leak could be the cause if this problem has slowly gotten worse over time.
Leaking Hose
Leaking Hose

Why ? Vacuum leaks typically start out small almost unnoticeable and gradually become worse due to heat and pressure inside the engine.

Any leak in the fuel system 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.

Check all hoses and clamps for loose connections or cracks.


Why would engine stall while idling: Fuel Injected System.

  • If the engine will stay running when you give it more throttle, check the idle air bypass valve.

Why ? By giving the engine more fuel 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 only occurs when the engine is cold 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.


Carbureted System: Engine stalls while idling.

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

Why ? By giving the engine more fuel when it is about to stall you are compensating for too low a idle. So,  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, 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.


Your oil light flickers.

Engine Oil Light
Engine Oil Light
  • 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.
  • You may have a clogged oil pick up screen. – Remove oil pan and replace or clean screen.
  • You may have worn out crank bearings or oil pump.

Engine Troubleshooting – When your heater blows cold air.

Thermostat Issues
Thermostat Issues

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. 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.

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.

  • You may have a clogged or restricted heater core.

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.

  • As a result, 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.

As a result, You may have a blown head gasket.


Engine troubleshooting – Uses coolant but I don’t see any leaks.

Intake Manifold Leak
Intake Manifold Leak

Why ? The intake gaskets seal water that flows between the two sides of your engine. Many times when these gaskets lose their ability to seal it allows coolant to leak into your engines crankcase.

Check your oil level. If the oil level is high 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.

Being able to fix engine problems takes years of experience, but anyone can make an effort to diagnose them. So, Next time your vehicle has an issue, don’t rely on a mechanic to tell you what’s wrong. Finally, Try using your senses to get an idea of what’s causing the problem.



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