ASE H2 Diesel Engines (Transit Bus) Feed

Question

A transit bus diesel engine cranks normally but will not start, and there is no smoke from the exhaust during cranking. Which condition is the most likely cause?

General Engine Diagnosis

Question · Medium

Question

Technician A says low engine power on a transit bus can be caused by a restricted air filter. Technician B says it can be caused by a plugged diesel particulate filter (DPF). Who is correct?

General Engine Diagnosis

Question · Easy

Question

During a manual cylinder cutout (cylinder contribution) test on a Cummins ISL, one cylinder produces no change in engine rpm when its injector is disabled. This indicates that the cylinder is:

General Engine Diagnosis

Question · Medium

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Question

A transit bus diesel produces continuous black smoke under acceleration. Which of these is the most likely cause?

General Engine Diagnosis

Question · Easy

Question

Blue-gray smoke from a transit bus diesel exhaust, especially at startup and during deceleration, most likely indicates:

General Engine Diagnosis

Question · Easy

Question

Persistent white smoke from a warmed-up transit bus diesel, accompanied by a gradually dropping coolant level and a sweet odor, most strongly points to:

General Engine Diagnosis

Question · Medium

Question

An engine oil sample analysis from a transit bus shows a high level of coolant (glycol) and elevated sodium/potassium. The most likely cause is:

General Engine Diagnosis

Question · Medium

Question

A transit bus diesel has low power and the ECM logs a fault for low boost pressure. The least likely cause of this fault is:

General Engine Diagnosis

Question · Medium

Question

When performing a cylinder compression test on a transit bus diesel, the most accurate procedure is to:

General Engine Diagnosis

Question · Medium

Question

A transit bus diesel has a steady knocking noise that increases with engine speed and is loudest under load. This is most consistent with:

General Engine Diagnosis

Question · Medium

Question

A transit bus diesel has excessive crankcase pressure (high blow-by). The most likely internal cause is:

General Engine Diagnosis

Question · Medium

Question

Technician A says a transit bus that idle-shuts down after a programmed time is malfunctioning. Technician B says programmable idle shutdown is a normal fuel-economy and emissions feature. Who is correct?

General Engine Diagnosis

Question · Easy

Question

A transit bus diesel surges and hunts at idle. Before condemning the ECM, the technician should first check for:

General Engine Diagnosis

Question · Easy

Question

On a common-rail transit bus diesel, the ECM reports rail pressure that will not reach commanded value at full load. The least likely cause is:

General Engine Diagnosis

Question · Hard

Question

A transit bus diesel runs well when cold but loses power and derates after about 20 minutes of route service. The best first diagnostic step is to:

General Engine Diagnosis

Question · Medium

Question

During a transit bus diesel hard-start complaint in cold weather, the technician should verify operation of the:

General Engine Diagnosis

Question · Medium

Question

A transit bus diesel exhibits low power only at the top of long grades, with no fault codes. Live data shows boost lower than expected. The most likely cause is:

General Engine Diagnosis

Question · Hard

Question

A transit bus diesel has an intermittent stall returning to idle from speed. The technician finds a partially restricted fuel filter. This restriction most directly causes:

General Engine Diagnosis

Question · Easy

Question

When interpreting a transit bus oil analysis report, a sudden spike in iron and aluminum with normal glycol and fuel readings most likely indicates:

General Engine Diagnosis

Question · Hard

Question

A transit bus diesel has rough running and a misfire isolated to one cylinder using cylinder cutout. The two most useful follow-up tests on that cylinder are:

General Engine Diagnosis

Question · Medium

Question

A transit bus diesel will crank but not start, and the technician notes the engine ECM does not receive a crankshaft position signal. The most appropriate next step is to:

General Engine Diagnosis

Question · Medium

Question

Technician A says excessive exhaust backpressure can reduce engine power on a transit bus. Technician B says a plugged or non-regenerating DPF is a common cause of excessive exhaust backpressure. Who is correct?

General Engine Diagnosis

Question · Medium

Question

A transit bus diesel has a 'low oil pressure' warning at hot idle but normal pressure at higher rpm. The least likely cause is:

General Engine Diagnosis

Question · Medium

Question

A transit bus operates a severe stop-and-go duty cycle. Compared with highway service, this duty cycle typically requires:

General Engine Diagnosis

Question · Easy

Question

A transit bus diesel has white smoke and a rough miss only until it warms up, then it clears. With no coolant loss, the most likely cause is:

General Engine Diagnosis

Question · Medium

Question

While road-testing a transit bus for a low-power complaint, the technician should monitor scan-tool data for all of the following EXCEPT:

General Engine Diagnosis

Question · Easy

Question

A transit bus diesel has an oil consumption complaint with blue smoke under load but not at idle. This pattern most likely indicates:

General Engine Diagnosis

Question · Hard

Question

A transit bus diesel sets an active engine derate with reduced torque and an illuminated malfunction lamp. The technician should FIRST:

General Engine Diagnosis

Question · Easy

Question

Excessive valve clearance (lash) on a transit bus diesel overhead-cam or pushrod valvetrain will most likely cause:

Cylinder Head Valve Train

Question · Easy

Question

Insufficient (too tight) valve clearance on a diesel engine is most likely to cause:

Cylinder Head Valve Train

Question · Medium

Question

During a cylinder head inspection on a transit bus diesel, the technician must check the head for flatness because a warped head can cause:

Cylinder Head Valve Train

Question · Medium

Question

Technician A says worn valve guides can cause oil consumption and blue smoke. Technician B says worn valve guides can also contribute to poor valve sealing. Who is correct?

Cylinder Head Valve Train

Question · Medium

Question

A cylinder leak-down test on a transit bus diesel shows air escaping from the engine oil filler/breather. This indicates leakage past the:

Cylinder Head Valve Train

Question · Medium

Question

When reassembling a transit bus diesel cylinder head, head bolts that specify a torque-to-yield (TTY) procedure must be:

Cylinder Head Valve Train

Question · Hard

Question

A burned exhaust valve found during a transit bus diesel head teardown is most commonly the result of:

Cylinder Head Valve Train

Question · Medium

Question

A weak or broken valve spring on a transit bus diesel can cause:

Cylinder Head Valve Train

Question · Medium

Question

Before removing the cylinder head on a transit bus diesel, the technician should:

Cylinder Head Valve Train

Question · Easy

Question

Measuring connecting rod bearing clearance on a transit bus diesel with Plastigage requires that the technician:

Engine Block Diagnosis

Question · Hard

Question

During a transit bus diesel overhaul, cylinder liner protrusion (liner height above the block deck) must be set within specification to:

Engine Block Diagnosis

Question · Hard

Question

A transit bus diesel cylinder block is found to have a cracked cylinder bore. The most appropriate action is to:

Engine Block Diagnosis

Question · Medium

Question

Excessive crankshaft end play on a transit bus diesel is most likely caused by:

Engine Block Diagnosis

Question · Medium

Question

When measuring cylinder bore taper on a transit bus diesel during overhaul, the largest wear is typically found:

Engine Block Diagnosis

Question · Hard

Question

Technician A says a deglazed (correctly honed) cylinder is needed for new rings to seat. Technician B says the proper crosshatch angle helps retain oil for ring lubrication. Who is correct?

Engine Block Diagnosis

Question · Medium

Question

During a transit bus diesel block overhaul, main bearing bore alignment (line bore) should be checked because misalignment can cause:

Engine Block Diagnosis

Question · Hard

Question

A transit bus diesel piston shows heavy scuffing on the thrust side and crown erosion. The most likely contributing cause is:

Engine Block Diagnosis

Question · Medium

Question

A transit bus diesel overheats in heavy stop-and-go service but is normal at highway speed. The most likely cause is:

Lubrication Cooling Systems

Question · Medium

Question

A transit bus diesel runs cooler than normal and the heater is weak. The most likely cause is:

Lubrication Cooling Systems

Question · Easy

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