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TEME practice questions

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Question 1Unverified Domain 1

In a diesel engine, the temperature at the end of compression is important mainly because it determines whether the fuel will ignite without a spark.

  1. ignite without a spark Correct answer.
  2. freeze inside the injector nozzle
  3. dissolve in the lubricating oil
  4. produce a vacuum in the crankcase

Explanation

A diesel engine relies on compression ignition, so the air must be heated enough by compression that injected fuel self-ignites. If the end-of-compression temperature is too low, ignition is delayed or fails, causing misfire and poor starting. This is why compression ratio and intake air temperature matter so much.

Question 2Unverified Domain 1

Which component opens and closes the valves of a four-stroke engine in time with the crankshaft?

  1. The injector pump
  2. The flywheel
  3. The turbocharger
  4. The camshaft Correct answer.

Explanation

The camshaft carries lobes that push the valve lifters, opening each valve at the correct point in the cycle and letting the spring close it. It is driven from the crankshaft at half speed in a four-stroke engine so that each valve operates once per two revolutions.

Question 3Unverified Domain 1

A technician finds that engine coolant is disappearing with no external leak and the exhaust is unusually white. Which fault best explains this?

  1. A failed head gasket Correct answer.
  2. A leaking radiator pressure cap
  3. A worn serpentine belt
  4. A clogged air filter

Explanation

Coolant entering the combustion chamber is vaporised and leaves as white steam in the exhaust, which also explains the loss of coolant without a visible puddle. A failed head gasket or cracked head is the usual path for this internal leak. Pressure-testing the cooling system and checking for combustion gases confirm the diagnosis.

Question 4Unverified Domain 1

What is the primary function of the lubrication system in an internal combustion engine?

  1. To increase the compression ratio
  2. To reduce friction and carry away heat Correct answer.
  3. To filter the intake air
  4. To atomise the fuel

Explanation

Oil forms a film between moving surfaces so they slide over one another with far less friction and wear. It also transports heat away from bearings and other hot spots and holds contaminants in suspension until the filter removes them.

Question 5Unverified Domain 1

In a four-stroke cycle, during which stroke does the piston move downward with both valves closed?

  1. Overlap stroke
  2. Power stroke Correct answer.
  3. Exhaust stroke
  4. Intake stroke

Explanation

The power stroke follows ignition, when burning gases push the piston down while both valves remain shut to contain the pressure. The intake stroke also moves the piston down, but the intake valve is open then. Keeping the valves closed during expansion is what converts combustion pressure into useful work.

Question 6Unverified Domain 1

Which statement correctly describes the relationship between engine torque and power?

  1. Torque equals power multiplied by displacement
  2. Torque and power are always numerically equal
  3. Power equals torque divided by displacement
  4. Power equals torque multiplied by angular speed Correct answer.

Explanation

Rotational power is the product of torque and angular velocity, so for a given torque, higher engine speed delivers more power. This is why an engine can make modest torque yet high peak power at high rpm. The two quantities are related but distinct.

Question 7Unverified Domain 1

Which fuel property most directly indicates how readily diesel fuel will self-ignite in a compression-ignition engine?

  1. Viscosity
  2. Cloud point
  3. Sulphur content
  4. Cetane number Correct answer.

Explanation

The cetane number rates a diesel fuel's ignition quality, with higher values indicating shorter ignition delay and easier self-ignition. Viscosity, sulphur and cloud point describe other characteristics such as flow, emissions and cold behaviour. Selecting fuel by cetane number helps ensure smooth, quiet combustion.

Question 8Unverified Domain 1

A vehicle's battery warning light stays on while the engine runs and the voltmeter reads about 12.2 volts. What is the most likely cause?

  1. The coolant thermostat is stuck open
  2. The fuel pump is failing
  3. The charging system is not producing enough voltage Correct answer.
  4. The starter motor is drawing too much current

Explanation

A healthy charging system should hold roughly 13.5 to 14.5 volts with the engine running. A reading near battery voltage indicates the alternator is not charging, so the warning lamp stays lit. Checking the belt, wiring and alternator output would confirm the fault.

Question 9Unverified Domain 1

An engine is said to have a compression ratio of 16:1. What does this figure compare?

  1. Intake air mass with exhaust gas mass
  2. Swept volume plus clearance volume with clearance volume Correct answer.
  3. Fuel flow at idle with fuel flow at full load
  4. Peak torque with peak power

Explanation

Compression ratio is the total cylinder volume with the piston at bottom dead centre divided by the volume remaining at top dead centre. The total equals swept volume plus clearance volume, and the remainder is the clearance volume alone. A higher ratio raises compression pressure and temperature.

Question 10Unverified Domain 1

Why is valve overlap used in many four-stroke engines?

  1. To prevent the piston from reaching top dead centre
  2. To reduce the compression ratio at high speed
  3. To keep both valves closed for the entire intake stroke
  4. To allow both valves to be open briefly around top dead centre and improve scavenging Correct answer.

Explanation

Overlap is the short period near top dead centre when intake and exhaust valves are both slightly open. The flowing exhaust gas helps draw in fresh charge, improving cylinder filling and scavenging, especially at higher speeds. Camshaft timing is chosen to balance this benefit against idle stability and emissions.

Question 11Unverified Domain 1

A turbocharged diesel engine has low power and black smoke under load, and the turbocharger shaft has excessive play. Which conclusion is best supported?

  1. The battery has a low state of charge
  2. The thermostat is opening too early
  3. The turbocharger is worn and delivering insufficient boost Correct answer.
  4. The fuel cetane number is too high

Explanation

Excessive shaft play indicates worn bearings, which allows the compressor to lose efficiency and leak oil. Insufficient boost leaves the engine over-fuelled for the air available, producing black smoke and reduced power. Measuring boost pressure and inspecting the compressor would confirm the diagnosis.

Question 12Unverified Domain 1

What is the purpose of the thermostat in an engine cooling system?

  1. To drive the water pump
  2. To remove air bubbles from the coolant
  3. To regulate coolant flow so the engine reaches and holds its design temperature Correct answer.
  4. To increase the boiling point of the coolant

Explanation

The thermostat stays closed while the engine is cold, allowing it to warm quickly, then opens to route coolant through the radiator. This keeps the engine near its design operating temperature for efficiency and low wear. It does not itself change the boiling point or pump the coolant.

Question 13Unverified Domain 1

During a cylinder leakage test, air escapes continuously from the radiator filler neck. What does this indicate?

  1. A leaking head gasket or cracked head Correct answer.
  2. A faulty spark plug gap
  3. Worn piston rings
  4. A stuck-open exhaust valve

Explanation

Air bubbling out of the cooling system during a leakage test shows that compressed air is passing from the cylinder into the coolant passages. That path is normally created by a failed head gasket or a crack in the head or block. Leakage past rings would instead be heard at the oil filler or dipstick tube.

Question 14Unverified Domain 1

Which condition most likely causes diesel engine knock or harsh combustion noise?

  1. A long ignition delay allowing fuel to accumulate before burning Correct answer.
  2. A restricted air filter at idle only
  3. A low oil level in the sump
  4. Excessively high coolant temperature

Explanation

If ignition delay is long, more fuel is injected before combustion starts, and that accumulated fuel then burns rapidly, producing a sharp pressure rise heard as knock. Higher cetane fuel, correct injection timing and adequate compression reduce the delay. Coolant temperature, filtration and oil level do not directly create this pressure spike.

Question 15Unverified Domain 1

What is the main advantage of a common rail fuel injection system over an older mechanical distributor pump system?

  1. It removes the need for a camshaft
  2. It allows the engine to run without compression
  3. It allows independent control of injection pressure and timing for each event Correct answer.
  4. It eliminates the need for a fuel filter

Explanation

In a common rail system, high-pressure fuel is stored in a rail and each injector is opened electronically. Because rail pressure is generated separately from injection timing, the engine controller can shape pressure, timing and multiple injection events independently. This improves combustion control, emissions and noise.

Question 16Unverified Domain 1

A compression test shows one cylinder much lower than the others, but adding a small amount of oil raises its reading noticeably. What does this suggest?

  1. Worn piston rings or cylinder bore Correct answer.
  2. A leaking intake manifold gasket
  3. Incorrect ignition timing
  4. A burned exhaust valve

Explanation

Oil temporarily seals the gap between rings and cylinder wall, so if the reading rises after adding oil, the loss is past the rings or bore. If the reading stays low, the leakage is more likely at a valve or head gasket. This wet-versus-dry comparison is the standard way to localise compression loss.

Question 17Unverified Domain 1

Which statement best explains why an engine's volumetric efficiency falls at very high speed?

  1. Fuel octane rating decreases with engine speed
  2. Flow losses through valves and ports rise faster than piston speed Correct answer.
  3. Oil pressure falls with engine speed
  4. Coolant temperature rises with engine speed

Explanation

As speed increases, the time available for intake flow shortens and friction losses in ports and valves grow with the square of flow velocity. Beyond a point, the cylinder can no longer be filled as completely, so volumetric efficiency drops. Camshaft timing and port design are chosen to shift this peak.

Question 18Unverified Domain 1

What does the term 'blow-by' refer to in an engine?

  1. Combustion gases escaping past the piston rings into the crankcase Correct answer.
  2. Fuel returning from the injector to the tank
  3. Coolant passing through the radiator
  4. Air entering the intake before the throttle

Explanation

Blow-by is combustion gas that leaks past the rings and piston into the crankcase, raising crankcase pressure and contaminating the oil. Excessive blow-by usually indicates worn rings, a damaged bore or a failed head gasket. Crankcase ventilation systems are designed to handle normal amounts.

Question 19Unverified Domain 1

An engine overheats only when the vehicle is stationary or in slow traffic, but runs at normal temperature at highway speed. Which cause fits best?

  1. A faulty cooling fan or fan control circuit Correct answer.
  2. A leaking head gasket
  3. A restricted fuel filter
  4. A stuck-closed thermostat

Explanation

At highway speed, ram air through the radiator provides enough cooling, but when stationary the system depends on the fan. If the fan does not run, temperature rises only at low speed and returns to normal once airflow increases. A thermostat fault would generally cause overheating at all speeds.

Question 20Unverified Domain 1

Which component stores energy from the combustion pulses and smooths crankshaft rotation?

  1. The camshaft
  2. The exhaust manifold
  3. The flywheel Correct answer.
  4. The oil pump

Explanation

The flywheel's mass absorbs energy during the power stroke and releases it during the other strokes, smoothing rotation and reducing vibration. It also provides a mounting surface for the clutch or torque converter. Camshaft, oil pump and manifold perform entirely different functions.

Question 21Unverified Domain 1

A cylinder balance test shows that disconnecting one cylinder's injector causes almost no change in engine speed. What does this most likely indicate?

  1. The engine is running perfectly on all cylinders
  2. The cooling system is over-pressurised
  3. The battery is failing
  4. That cylinder is contributing little or no power Correct answer.

Explanation

If cutting fuel to a cylinder does not reduce engine speed, that cylinder was not producing useful power in the first place. The cause could be a faulty injector, low compression, or an ignition or valve problem on that cylinder. Comparing each cylinder's contribution isolates the weak one.

Question 22Unverified Domain 1

What is the main purpose of exhaust gas recirculation in a diesel engine?

  1. To lower combustion temperature and reduce nitrogen oxide formation Correct answer.
  2. To raise the cetane number of the fuel
  3. To increase peak power output
  4. To increase the compression ratio

Explanation

Recirculating a portion of exhaust gas into the intake dilutes the fresh charge and lowers peak combustion temperature. Nitrogen oxides form mainly at high temperature, so this reduction in temperature cuts their formation. The trade-off is increased particulate matter if EGR is excessive.

Question 23Unverified Domain 1

An engine has a high-pitched whine that rises with engine speed and is loudest from the timing cover area, with the accessory belt removed. Which component should be investigated?

  1. The alternator bearing
  2. The fuel tank sender
  3. The water pump seal
  4. The timing chain or belt tensioner Correct answer.

Explanation

With the accessory belt removed, the alternator and water pump are no longer driven, so a noise that persists points to the timing drive. A worn chain, belt or tensioner can produce a whine or rattle that tracks engine speed. Inspecting the timing components for wear and correct tension is the next step.

Question 24Unverified Domain 1

Why can a diesel engine with a very high compression ratio experience higher mechanical stress than a lower-compression petrol engine?

  1. Because petrol engines cannot use a flywheel
  2. Because higher compression reduces the amount of air drawn in
  3. Because diesel fuel has a lower energy content per litre
  4. Because peak cylinder pressure rises with compression ratio and loads the pistons, rods and bearings Correct answer.

Explanation

Raising compression ratio increases the pressure and temperature reached at the end of compression, and combustion adds a further sharp pressure rise. These higher peak pressures impose greater loads on pistons, connecting rods, bearings and the cylinder head. Components in high-compression diesel engines are therefore built heavier to withstand the stress.

Question 25Unverified Domain 1

A diesel engine starts easily when cold but loses power and emits grey-white smoke once warmed up, and the injection timing is found to be retarded. What is the most likely explanation?

  1. The turbocharger wastegate is stuck closed
  2. The battery is overcharged
  3. Fuel is being injected too late for complete combustion, so unburned fuel leaves as smoke Correct answer.
  4. The coolant thermostat is stuck open

Explanation

Retarded injection timing delays combustion until after top dead centre, so burning continues late into the expansion stroke and some fuel escapes unburned. That produces grey-white smoke, poor efficiency and reduced power, particularly once the engine is warm. Correcting the timing restores combustion phasing.

Question 26Unverified Domain 1

Which component in a diesel fuel system removes large particles and water before the fuel reaches the high-pressure pump?

  1. The injection nozzle
  2. The lift pump check valve
  3. The primary fuel filter/water separator Correct answer.
  4. The fuel return line

Explanation

The primary filter and water separator sit on the suction side of the system and trap coarse debris and entrained water before fuel reaches sensitive high-pressure components. Nozzles and check valves meter or control flow but do not perform bulk filtration.

Question 27Unverified Domain 1

What is the primary function of the lift pump in a diesel fuel system?

  1. To advance injection timing with engine speed
  2. To regulate the maximum injection pressure
  3. To supply low-pressure fuel from the tank to the high-pressure pump Correct answer.
  4. To atomize fuel into the combustion chamber

Explanation

The lift pump provides a steady low-pressure supply of fuel from the tank to the inlet of the high-pressure injection pump. Atomization, timing control, and pressure regulation are handled by other components downstream.

Question 28Unverified Domain 1

In a four-stroke diesel engine, during which stroke is air drawn into the cylinder?

  1. The power stroke
  2. The exhaust stroke
  3. The intake stroke Correct answer.
  4. The compression stroke

Explanation

The intake stroke draws fresh air through the open intake valve as the piston moves down the bore. Compression, power, and exhaust follow in sequence after the intake valve closes.

Question 29Unverified Domain 1

Which statement correctly describes the purpose of a diesel particulate filter?

  1. It traps soot particles from the exhaust and periodically burns them off Correct answer.
  2. It converts nitrogen oxides into nitrogen and water
  3. It cools the exhaust gas before it leaves the tailpipe
  4. It meters the amount of fuel injected per cycle

Explanation

A particulate filter captures soot on a porous substrate and later regenerates by oxidizing the accumulated particles at high temperature. NOx conversion is the role of selective catalytic reduction or a lean NOx trap, not the filter.

Question 30Unverified Domain 1

What does the term 'injection duration' describe?

  1. The interval between two successive injection events
  2. The pressure difference across the nozzle
  3. The angle between the nozzle axis and the piston crown
  4. The length of time the injector remains open during one injection event Correct answer.

Explanation

Injection duration is the time, or crank angle, during which the injector nozzle is open and delivering fuel. Longer duration generally delivers more fuel per cycle and influences combustion phasing.

Question 31Unverified Domain 1

What is the main purpose of a glow plug in an indirect-injection diesel engine?

  1. To warm the combustion chamber for easier cold starting Correct answer.
  2. To ignite the fuel throughout normal running
  3. To increase injection pressure at low speed
  4. To measure combustion chamber temperature

Explanation

A glow plug heats the prechamber or swirl chamber so that compression alone can ignite fuel during cold starting. Once the engine warms, combustion is sustained by compression heat without glow plug assistance.

Question 32Unverified Domain 1

Which unit is commonly used to express diesel injection pressure in service specifications?

  1. Degrees Celsius
  2. Bar or megapascals Correct answer.
  3. Ohms
  4. Litres per minute

Explanation

Injection pressure is a pressure measurement and is expressed in bar, kilopascals, or megapascals. Litres per minute describes flow, Celsius describes temperature, and ohms describes resistance.

Question 33Unverified Domain 1

What does the term 'fuel rail' refer to in a common rail system?

  1. A mechanical linkage connecting the injectors
  2. A manifold that stores high-pressure fuel and distributes it to each injector Correct answer.
  3. A return pipe that carries leakage fuel back to the tank
  4. A low-pressure line feeding the lift pump

Explanation

The rail is a high-pressure accumulator that holds pressurized fuel and feeds each injector through short high-pressure lines. It smooths pressure pulsations and allows injection pressure to be controlled independently of engine speed.

Question 34Unverified Domain 1

A diesel engine cranks normally but will not start, and no fuel is found at the injector high-pressure lines. Which area should be checked first?

  1. The low-pressure supply, including tank pickup, filters, and lift pump Correct answer.
  2. The turbocharger compressor wheel
  3. The radiator cap pressure rating
  4. The exhaust gas recirculation valve position

Explanation

If no fuel reaches the high-pressure lines, the fault most likely lies in the low-pressure supply chain such as a blocked filter, air leak, or failed lift pump. Confirming supply pressure first narrows the diagnosis before suspecting high-pressure components.

Question 35Unverified Domain 1

An engine runs rough at idle and smooths out at higher speed, and a cylinder cutout test identifies one weak cylinder. Which cause is most consistent with these symptoms?

  1. A partially blocked or worn injector nozzle on that cylinder Correct answer.
  2. A faulty coolant thermostat
  3. An undercharged battery
  4. A restricted air filter element

Explanation

A weak cylinder that improves at higher speed often points to poor fuel atomization or delivery from a worn or partially clogged nozzle. At higher speeds and loads the injected quantity increases, masking the imbalance.

Question 36Unverified Domain 1

Why is diesel fuel filtered to a much finer degree than gasoline in many applications?

  1. Diesel engines run at lower compression than gasoline engines
  2. Diesel fuel contains more dissolved air than gasoline
  3. High-pressure injection components have very tight clearances and are easily damaged by small particles Correct answer.
  4. Diesel fuel is more volatile and evaporates quickly

Explanation

Diesel injection pumps and nozzles operate with micron-level clearances at very high pressure, so abrasive particles cause rapid wear and seizure. Fine filtration protects these precision components.

Question 37Unverified Domain 1

What happens to injection timing in a simple mechanical distributor pump as engine speed increases if no advance mechanism is fitted?

  1. Injection occurs later in crank-angle terms because pump delivery is time-based Correct answer.
  2. Injection timing remains exactly constant in crank-angle terms
  3. Injection occurs earlier because pressure rises faster
  4. Injection is disabled above a set speed

Explanation

A purely time-based pump delivers fuel at a fixed interval after the start of pumping, so as speed rises the same time delay corresponds to a larger crank angle, retarding timing. Advance mechanisms exist to compensate for this effect.

Question 38Unverified Domain 1

A vehicle with a common rail diesel has a long crank time and a fault code for low rail pressure during cranking. Which component is most likely responsible?

  1. The intercooler
  2. The rail pressure control valve or pressure sensor circuit Correct answer.
  3. The exhaust gas recirculation cooler
  4. The alternator diode pack

Explanation

Rail pressure during cranking is regulated by the pressure control valve and monitored by the rail pressure sensor. A fault in either the valve or sensor circuit prevents the control unit from building or reading adequate pressure, delaying start.

Question 39Unverified Domain 1

Which statement best explains why diesel engines generally produce more torque at low speed than comparable gasoline engines?

  1. They use spark plugs to ignite a lean mixture
  2. They operate at higher rotational speed limits
  3. They have larger throttle plates for better airflow
  4. They use high compression and direct injection of a fuel with high energy density, giving strong low-speed combustion Correct answer.

Explanation

High compression ratios and direct injection of energy-dense diesel fuel produce high cylinder pressures early in the power stroke, yielding strong torque at low speed. Diesel engines typically run at lower maximum speeds than gasoline engines.

Question 40Unverified Domain 1

What is the purpose of the spill or return port on a mechanical injector?

  1. To increase the nozzle opening pressure
  2. To admit air into the injector for atomization
  3. To store fuel for the next injection event
  4. To allow excess fuel and leakage to return to the tank, cooling and lubricating the injector Correct answer.

Explanation

Leakage fuel past the needle and control plunger must escape so pressure does not build behind the needle and disturb opening. The return path carries this fuel back to the tank while cooling and lubricating internal parts.

Question 41Unverified Domain 1

Why must diesel fuel injection lines be of equal length and rigid construction in a multi-cylinder mechanical system?

  1. To simplify the routing of the return circuit
  2. To allow the lines to flex with engine vibration
  3. To keep hydraulic delay and pressure wave timing consistent between cylinders Correct answer.
  4. To reduce the total weight of the engine

Explanation

Pressure waves travel through fuel at a finite speed, so unequal line lengths would create different hydraulic delays and injection timing between cylinders. Rigid lines also resist expansion that would damp pressure waves.

Question 42Unverified Domain 1

Which condition would cause a diesel engine to emit continuous white smoke after warm-up?

  1. A slightly rich air-fuel ratio at full load
  2. Normal regeneration of the particulate filter
  3. Unburned fuel passing through the engine, such as from a faulty injector or low compression Correct answer.
  4. Complete combustion with excess air

Explanation

White smoke is largely vaporized but unburned fuel, indicating poor combustion from low compression, incorrect injection timing, or a leaking injector. It is distinct from black smoke caused by over-fuelling under load.

Question 43Unverified Domain 1

A technician finds that the engine oil level is rising and smells strongly of diesel fuel. Which fault is most likely?

  1. A failed thermostat
  2. Fuel leaking past the injection pump shaft seal or a leaking injector into the crankcase Correct answer.
  3. A blocked crankcase breather only
  4. A worn turbocharger compressor wheel

Explanation

Fuel can enter the sump through a leaking high-pressure pump shaft seal or a leaking injector, diluting the oil and raising the level. This condition reduces lubrication and should be corrected promptly.

Question 44Unverified Domain 1

What is the effect of excessive nozzle opening pressure on injection?

  1. Fuel is injected earlier and atomization worsens
  2. Fuel is injected later and atomization improves, but the pump load increases Correct answer.
  3. The injector return flow stops completely
  4. Injection quantity increases without any timing change

Explanation

A higher opening pressure delays the start of injection slightly and produces finer atomization because fuel is forced through the nozzle at higher velocity. The injection pump must work harder to overcome the higher threshold.

Question 45Unverified Domain 1

Which statement correctly describes the role of the engine control unit in a modern common rail diesel?

  1. It calculates injection quantity, timing, and pressure from sensor inputs and commands the injectors Correct answer.
  2. It controls only the glow plug circuit
  3. It mechanically drives the injector needles through a camshaft
  4. It filters the fuel before it reaches the rail

Explanation

The control unit processes signals such as rail pressure, air mass, and engine speed to determine injection quantity, timing, and pressure, then commands the injectors electrically. Mechanical camshaft actuation belongs to older systems.

Question 46Unverified Domain 1

A diesel engine produces a rhythmic knocking sound that increases with load and is traced to one cylinder. Which fault is most likely?

  1. A leaking exhaust manifold gasket
  2. An injector delivering too much fuel or with poor spray pattern on that cylinder Correct answer.
  3. A loose accessory drive belt
  4. A restricted coolant passage

Explanation

Over-fuelling or poor atomization on one cylinder causes a rapid pressure rise and audible knock that worsens with load. Isolating the cylinder with a cutout test confirms the affected injector.

Question 47Unverified Domain 1

Why does a diesel engine with a worn injection pump often show reduced power and increased exhaust smoke simultaneously?

  1. The pump reduces compression ratio
  2. The pump adds extra air to the intake charge
  3. The pump begins to filter the fuel less effectively
  4. Delivery quantity and timing become inaccurate, so combustion is both weaker and incomplete Correct answer.

Explanation

Wear in the pumping elements and control mechanism causes inconsistent delivery and timing, so some cycles are under-fuelled and others over-fuelled. This reduces useful work while producing unburned or partially burned exhaust.

Question 48Unverified Domain 1

A common rail diesel develops a sudden loss of power and enters limp mode, with codes for rail pressure above target. Which fault best explains this?

  1. A faulty coolant temperature sensor
  2. A sticking rail pressure control valve or a restricted fuel return line Correct answer.
  3. A clogged air filter element
  4. A worn accessory drive belt

Explanation

If the pressure control valve sticks or the return line is restricted, the rail cannot shed excess pressure, so measured pressure exceeds target and the control unit limits output. Checking valve operation and return flow isolates the cause.

Question 49Unverified Domain 1

In a distributor-type injection pump, what is the function of the delivery valves?

  1. To regulate the engine idle speed
  2. To advance injection timing with load
  3. To filter abrasive particles from the fuel
  4. To hold residual pressure in the injector lines and prevent back-flow after each delivery Correct answer.

Explanation

Delivery valves close after each pumping stroke to maintain a controlled residual pressure and prevent high-pressure gas from flowing back toward the pump. This residual pressure supports rapid, consistent injector opening on the next stroke.

Question 50Unverified Domain 1

A diesel engine has good compression, correct timing, and adequate fuel supply, yet it misfires only under heavy load. Which factor is most likely?

  1. A disconnected tachometer signal
  2. An overfilled cooling system
  3. Excessive glow plug operation after warm-up
  4. Insufficient fuel delivery volume at high demand, such as a weak lift pump or restricted filter Correct answer.

Explanation

A fuel supply that is adequate at light load may fall short when demand peaks, causing a lean misfire or power loss under heavy load. Checking supply pressure and filter restriction under load confirms the diagnosis.