Engine Troubleshooting FAQ – Repair Issues, With Solutions


This page provides engine troubleshooting answers, to some of the most frequently asked questions, about automotive repair and service.

In comparison to wrenching, engine troubleshooting, requires a more in-depth knowledge, of the workings of an engine. So, a mechanically inclined person, can easily change a part and do a good job of it. But, it takes a higher level of study, to be able to accurately determine, which part needs to be changed.


Exhaust Smoke

Engine Troubleshooting
Exhaust 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. But, if the air filter is not clogged, it could be a sensor issue, 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. But, 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. Furthermore, 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 have, leaking turbocharger seals.


Engine Troubleshooting, Why Does Your Vehicle, Smell Like Rotten Eggs:

The rotten egg smell, is the result of unburned fuel vapors, reacting with chemicals in the catalytic converter. As a result, 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, the choke plate may be stuck or you may have, a vacuum leak.


Your Vehicle, Lacks Power:

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 rough, especially when idling, it may be due to, old/failing spark plugs and wires.

Engine Troubleshooting
Failing Spark Plugs

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:

  • 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, but, 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 Troubleshooting, Shakes, While Idling

This is a telltale sign that the engine is misfiring, on one or more cylinders.

Engine Troubleshooting
Shakes While Driving

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.


Does Your Vehicle Have Hesitation, 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. Most often, due to heat and pressure, inside the engine.

Engine Troubleshooting
Vacuum Leak

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 vehicle’s computer. As a result, it 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. And, often result in hesitant or jerky operation.


Does Your Vehicle Stall, 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.

Why ? Vacuum leaks typically start out small, almost unnoticeable and gradually become worse. Most often, due to heat and pressure, inside the engine. So, any leak in the fuel system vacuum, will intermittently throw off the air/fuel mixture. This results in a hesitation, jerking or in extreme situations, stalling. Finally, check all hoses and clamps, for loose connections or cracks.


Engine Troubleshooting, 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 adding more fuel, when its stalling, you are compensating for, a faulty idle air bypass valve. So, 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 cold.

Another possibility is, a faulty fuel pressure regulator.

Faulty Fuel Pressure Regulator
Faulty Fuel Pressure Regulator

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.

Why would engine stall, while idling (Carbureted System).

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

Why ? By adding more fuel, when its stalling, 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. Therefor, 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.


Engine Troubleshooting, Your Oil Light Warning, Flickers:

  • Your 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.
  • Low oil pressure. You may have worn out crank bearings or oil pump.

Engine 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. So, as the coolant temperature increases, the thermostat opens to increase coolant flow.

Bad Thermostat
Bad Thermostat

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. So, if it isn’t hot enough, change the thermostat. Also, check the rad cap.

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 isn’t flowing through as it should. As a result, it is cooling down and that translates into, your heater blowing cool or warm air.

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. Even worse, you may have a blown head gasket.


Engine Troubleshooting – Uses Coolant, But I Don’t See Any Leaks.

Consequently, your intake gasket may be leaking.

Why ? The intake gaskets seal coolant, 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.

Intake Gasket Leak
Intake Gasket Leak

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.

Above all, engine troubleshooting, 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. In other words, try using your senses to get an idea, of what’s causing the problem.




منبع: https://dannysengineportal.com/engine-troubleshooting-faq-automotive-repair-issues-with-solutions/