ASE T2 practice test: diesel engines

Incorrect: Staged tightening in sequence is right, but Technician B is also right that the maker decides whether threads and bolt heads are oiled.

Incorrect: Lubricating only as specified is right, and so is Technician A's staged sequence; both control clamp load.

Correct: Head bolts are brought up in stages in the specified sequence, and threads and under-head faces get exactly the lubricant the maker calls for, because oil or no oil changes the clamp load at a given torque.

Incorrect: Both are standard head installation practice: staged tightening in sequence, and lubrication only as the maker specifies.

Incorrect: Dirt pulled through the intake wears the bore and rings from the inside, not the outer coolant-side wall.

Incorrect: Too much SCA leaves deposits and gel that clog passages and hurt heat transfer; it does not erode the liner wall.

Correct: Pitting on the coolant side of a wet liner is cavitation erosion from liner vibration; nitrite in the coolant forms the protective film, so a low level lets the pits form.

Incorrect: A thermostat stuck closed causes overheating, not small, deep pits on the coolant side of the liner.

Correct: An air pocket left after a refill keeps coolant from reaching the gauge sender and the heater core, so the gauge swings and the heater blows cold.

Incorrect: A cap that opens early loses coolant and lowers the boiling point; it does not make the heater blow cold right after a refill.

Incorrect: A restricted radiator core causes steady overheating under load, while the heater still gets hot coolant.

Incorrect: A slipping fan clutch makes the engine run hot under load, and the heater stays hot; it does not make the gauge swing after a refill.

Correct: If the turbo shaft play is good, oil in the compressor housing points to oil that cannot drain from the center housing, and a restricted drain line backs it up past the seals.

Incorrect: Fuel rail pressure has nothing to do with the turbocharger's oil seals.

Incorrect: A wastegate stuck open reduces boost; it does not put oil into the compressor housing.

Incorrect: A leaking charge air cooler outlet hose loses boost air but does not bring oil into the compressor.

Incorrect: Loosening a fitting on a running rail engine releases a dangerous high-pressure spray.

Incorrect: A glove gives no protection: a high-pressure spray can pierce it and inject fuel under the skin, a medical emergency.

Incorrect: Soapy water works for air leaks; fuel on a high-pressure line will not form bubbles the way air does, and getting close to the line is unsafe.

Correct: Common rail fuel is under enough pressure to cut through skin, so a leak is found by holding cardboard near the line and watching for spray, never with the hand.

Incorrect: Low-pressure supply affects every cylinder's fuel feed, and it is not part of an injector installation.

Incorrect: A rail pressure regulator belongs to a common rail system; cam-actuated unit injectors have no rail pressure to set.

Correct: On cam-actuated unit injectors, the injector height (preload) sets how far the plunger travels; setting it wrong upsets fuel delivery and timing, which causes black smoke and poor acceleration.

Incorrect: Injection control pressure is a HEUI oil setting; cam-actuated unit injectors do not use it.

Incorrect: A return line leaking outside the valve cover drips fuel on the engine, not into the oil.

Incorrect: A restricted tank vent starves the engine of fuel; it does not put fuel into the oil.

Incorrect: A worn transfer pump lowers supply pressure and power; it has no path into the crankcase.

Correct: On side-fed injectors the connector tube seals against the injector inside the head, so a leaking tube seal lets fuel drain into the crankcase.

Incorrect: Bending the mating pin damages a second terminal and still leaves a poor connection.

Incorrect: Dielectric grease seals out moisture but does not make a loose terminal grip again.

Incorrect: Tape around the connector does nothing for the loose contact inside it.

Correct: A female terminal that is loose on the correct gauge pin has lost its spring tension and must be replaced to make a reliable contact.

Incorrect: High-pressure lines are pre-formed and must not be bent by hand, so Technician A is wrong, and Technician B is wrong too.

Incorrect: Overtightening deforms the sealing cone and causes leaks; fittings are torqued to specification, so Technician B is wrong.

Incorrect: Neither practice is allowed: bending a line by hand kinks or weakens it, and overtightening ruins the seat.

Correct: High-pressure lines are installed exactly as formed, without being bent, and the fittings are torqued to specification; both statements break those rules.

Correct: A 7 psi loss against a 5 psi limit fails the test, so the cooler is repaired or replaced; cleaning the fins improves airflow but cannot seal a leak.

Incorrect: The test measures leaks in the cooler's core and tanks; cleaning the outside fins cannot stop internal pressure loss, so Technician B is wrong.

Incorrect: Only Technician A is right; fin cleaning does nothing for a pressure leak.

Incorrect: Technician A is right: a loss over the manufacturer's limit means the cooler must be repaired or replaced.

Correct: On a four-stroke, each cylinder fires once every two crank turns, so one weak or dead cylinder makes a disturbance at half of crankshaft speed.

Incorrect: Unequal driveshaft angles cause vibration at twice driveshaft speed while driving, not at idle.

Incorrect: An out-of-balance flywheel turns with the crank, so it vibrates at crankshaft speed (first order), not half of it.

Incorrect: Fan imbalance vibrates at fan speed, which depends on the drive ratio and the fan clutch, not at exactly half of crank speed.

Incorrect: Air in the suction line gives a rough idle or stall at random times, not a clean stop after five minutes.

Correct: Many trucks have a programmable idle shutdown timer that stops the engine after a set idle time with the parking brake set, and it sets no fault code.

Incorrect: A plugged tank vent starves the engine slowly under load; it would not stop it at exactly the same idle time.

Incorrect: A failed oil pressure circuit would log a fault code; an engine protection shutdown does not follow a parked-idle timer.

Incorrect: A misadjusted clutch switch can keep the engine brake off, but an active ABS event or fault also disables it, so Technician B is right too.

Incorrect: ABS shuts off the engine brake during an event or fault, but a misadjusted clutch switch can also stop it from working.

Correct: Engine brake controls need the clutch released and no ABS activity; a misadjusted clutch switch or an ABS event or fault can each keep it off.

Incorrect: Both inputs can disable the engine brake: the clutch pedal switch and the ABS signal.