A1: Engine Repair

An engine compression test will detect air leakage from the intake valves, exhaust valves, piston rings, and/or the cylinder head gasket. While it can identify a loss caused by any combination of these components, it is limited to detecting leaks only within them.

If an engine starts producing a knocking sound that varies with RPM but disappears during a balance test, the most likely cause is wear or damage to one or more connecting rod bearings. These bearings link the crankshaft to the connecting rods, which in turn connect to the pistons. When a bearing is worn or damaged, it can allow the connecting rod to strike the crankshaft, creating a knocking noise that changes with engine speed. A balance test, which involves disabling each cylinder one at a time, can help isolate issues with specific cylinders or connecting rods. If the knock disappears during this test, it suggests a connecting rod bearing may be failing—though not yet enough to throw the engine significantly out of balance.

Both technicians are correct.
A blown head gasket can allow coolant to leak into the combustion chamber, where it mixes with the air/fuel mixture and burns during combustion. This can cause problems such as reduced engine performance, overheating, and potential engine damage.

Additionally, a blown head gasket may cause the engine oil to appear milky or frothy. This happens when coolant enters the oil passages through the damaged gasket and mixes with the engine oil. If left unaddressed, this contamination can lead to serious engine damage.

Technician B is correct because issues affecting the combustion of the air/fuel mixture—known as fuel propagation—can be observed within the spark line on an oscilloscope.

Technician A is incorrect in stating that the voltage required to maintain a spark is called the sparkline. In reality, the sparkline refers to the duration of current flow across the spark plug gap. This duration is influenced by the resistance in the secondary circuit, not the primary, and the available coil voltage. In direct injection (DI) systems, typical firing voltage ranges from 8 to 10 kilovolts (kV). A proper sparkline should be smooth and consistent, generally lasting between 1.2 and 2 milliseconds. If the sparkline is short or irregular—similar to when firing voltages are high—it usually indicates excess resistance in the secondary ignition circuit.

To check if a valve spring is square, place it on a flat surface and use a machinist’s square. Slowly rotate the spring — all coils should align evenly with the square. If any coil lifts away, the spring may be out of square. To check for precision, use a feeler gauge between the coil and the square to confirm it meets the required tolerance.

To measure the installed height of a valve spring, do so with the spring fully assembled in the cylinder head. This measurement is the distance from the spring seat (or pocket) in the head to the underside of the retainer. Use a caliper or specialized gauge for accurate results.

Many small moving parts within the valvetrain can generate noise, but among the options provided, only the rocker arms are actually part of the valvetrain.

If an engine overheats at cruising speed but returns to normal at idle, a restricted radiator is the most likely cause. This limits coolant flow, often due to debris buildup or a faulty thermostat. While issues like a bad radiator cap or fan relay can cause overheating, they’re less likely here since both cooling fans are working. Prompt diagnosis is crucial to prevent engine damage.

Black exhaust smoke is often caused by a rich air-fuel ratio, where too much fuel and not enough air leads to incomplete combustion. This can result from issues like a faulty fuel injector, clogged air filter, bad oxygen sensor, or malfunctioning mass airflow sensor.

In contrast, a lean mixture may cause white or gray smoke, while burning oil or coolant can produce blue or gray smoke. Diagnosing abnormal exhaust is key to maintaining engine performance and emissions compliance.

A hissing sound at the tailpipe during a cylinder leakage test typically indicates a leaking exhaust valve or a damaged valve seat, allowing air to escape from the combustion chamber. While worn piston rings or a bent intake valve can also cause leaks, they usually present with other signs, such as intake noise, low compression, or oil consumption.

A faulty rod bearing causes a knocking noise that changes with RPM and typically stops when the cylinder is shorted.

Always refer to the OEM-specific procedure to determine whether valve adjustments should be done hot or cold.

Technician A is correct: the closed coil end of a valve spring should face the cylinder head. Technician B is incorrect—not all valve springs use shims to control assembled height, and the correct term should be “assembled height,” not something else.

When two side-by-side cylinders are underperforming, a blown head gasket is often the cause. Positioned between the engine block and cylinder head, the head gasket seals the combustion chambers to maintain proper compression. A leak between adjacent cylinders can cause compression loss, reducing power, efficiency, and often leading to misfires.

During an engine compression test, several air leak-related issues can be identified:

Worn piston rings – Allow air to leak past, causing low compression in one or more cylinders.

Burned or damaged valves – Prevent proper sealing, also leading to low compression.

Cracked or warped cylinder head – Can result in poor sealing and compression loss.

Blown head gasket – May leak air between cylinders or into the cooling system, causing compression loss and possible overheating.

Note: A compression test does not check for air leaks in the PCV valve, which controls crankcase vapor flow and is not part of the combustion sealing system.

A loose timing belt is likely the cause, often producing a flapping noise near the front of the engine. In contrast, a loose drive belt typically causes a squeaking sound.

A dial indicator is a precision tool used to measure crankshaft endplay—the axial movement of the crankshaft within the engine block. It’s usually mounted on a stand secured to the engine, with the probe positioned against the crankshaft end to detect movement.

If a customer reports white smoke from the exhaust, the cooling system should be checked first for low fluid levels. White smoke often indicates coolant is leaking into the combustion chamber, possibly due to a blown head gasket, cracked head, or damaged block. Burning coolant produces white exhaust and may also lead to overheating. While other fluids should be checked, they’re less likely to cause this issue.

Issues with how fuel or air burns are known as fuel propagation problems, which appear within the spark line. Technician A is incorrect—the spark line duration depends on total secondary circuit resistance and available coil voltage. In a DI system, typical firing voltage is 8–10 kV, with normal current flow lasting 1.2–2 milliseconds.

Both Technician A and Technician B are correct, as they address different aspects of piston movement.

Technician A is right that piston pin offset shifts the pin slightly toward the engine’s thrust side. This offset helps reduce piston slap and improves efficiency by aligning the piston’s center of mass closer to the thrust side.

Technician B is also correct that piston side thrust is greatest during the power stroke. This force occurs due to the connecting rod’s angle and piston pin offset, with maximum thrust happening as combustion pushes the piston down.

A faulty main bearing can cause a distinct thumping noise when the engine first starts. This issue may also lead to temporarily low oil pressure, which often normalizes after the engine runs for a short time. In some cases, the check oil light may briefly appear, though it doesn’t always occur.

Both Technician A and Technician B may be correct, depending on the circumstances.

In high-mileage engines, a ridge often forms near the top of the cylinder bore due to wear at the upper limit of the piston stroke. This ridge can obstruct piston removal, which supports Technician A’s recommendation to remove it before extracting the pistons.

Technician B is also correct in warning that leaving the ridge can damage new piston rings. Since these rings must seat tightly against the cylinder walls, the ridge can interfere with proper installation, leading to premature wear or failure.

In conclusion, removing the ridge is generally recommended. It eases piston removal and helps ensure the longevity and proper function of the new piston rings.

Air pockets can sometimes become trapped in the cooling system after it’s drained and refilled, disrupting coolant flow and causing the engine to overheat—even if the radiator hose, coolant level, and other components are functioning properly. To resolve this, the system must be “bled” to release trapped air. This is typically done by running the engine with the heater on and the radiator cap open, adding coolant as needed. If overheating continues after bleeding, further diagnosis is necessary to identify the underlying issue.

Technician A is correct in recommending the use of a machinist ruler to measure the installed height of the valve tip. This height refers to the distance from the valve spring seat to the tip of the valve when it is fully closed. Accurate measurement is essential for maintaining proper valve train geometry, which directly impacts valve timing and overall engine performance. Measuring the installed height ensures the valve is correctly positioned within the engine.

Both Technician A and Technician B are correct.

Technician A is right in stating that specific gravity measurements can help indicate a battery’s state of charge. However, this is just one of several factors to consider—battery age, temperature, and load history also play important roles in assessing its condition.

Technician B is also correct. A voltage reading below 9.6 volts at 70°F typically signals that the battery has failed a capacity test and cannot hold a charge. Still, this should be confirmed with additional methods such as load testing, which provides a more comprehensive evaluation.

In summary, both technicians provide valid insights into battery testing and diagnosis.

Correct Answer: Cracked Cylinder Wall

A cracked cylinder wall is a common form of engine block damage, particularly in high-performance or large engines. These cracks can allow coolant to seep into the combustion chamber, disrupting engine operation. One of the most noticeable signs of this issue is white smoke from the exhaust, which results from coolant being burned during combustion.

Technician A is correct. Hydraulic lifters require a small amount of preload—slight tension applied to ensure proper operation and reduce valve train noise. Setting lifters to zero lash (no preload) can prevent them from functioning correctly, potentially causing performance issues.

Technician B, however, is incorrect. While adjusting the nuts does affect preload, overtightening them can result in excessive preload. This may lead to valve train damage or reduced engine performance. Proper adjustment is key to maintaining engine reliability.

Grinding the valve stems is a common method used to correct reduced clearance between the rocker arm and the pushrod. This reduction can occur when the cylinder head is machined or when shorter pushrods are installed.

If the clearance is too tight, the valves may not open fully, leading to a drop in engine power and performance. By grinding the valve stems, proper valve lift is restored, allowing the engine to operate efficiently.

The extent of grinding required depends on how much the clearance has changed. Because this is a precise procedure, it should be performed by a qualified mechanic.

The radiator cap acts as a pressure regulator for the cooling system. As the engine heats up, the coolant expands, increasing pressure within the system. The cap’s pressure relief valve releases this excess pressure to maintain safe operating conditions. However, if the radiator cap is faulty and fails to release pressure properly, it can cause excessive pressure buildup. This can lead to a burst or leaking radiator hose, ultimately resulting in a damaged or broken hose.

If a hissing sound is heard from the throttle body during a cylinder leakage test, it indicates a leaking intake valve. The noise results from air escaping past the intake valve and into the intake manifold.

In this test, compressed air is introduced into the cylinder through the spark plug hole, and any pressure loss is measured. A leak past the intake valve means it isn’t sealing properly, which can lead to reduced engine performance, higher fuel consumption, and possible engine damage if not addressed.

In this case, the engine likely has a faulty intake valve that requires repair or replacement.

Valve spring free length is a critical specification checked during engine assembly. It refers to the length of the valve spring when fully relaxed (not compressed) and directly affects the spring’s ability to keep the valve closed and return it after camshaft actuation.

To inspect free length, the spring is removed and measured with a spring gauge. The reading is then compared to the manufacturer’s specifications. If it falls outside the acceptable range, the spring must be replaced to maintain proper engine performance.

Technician A is correct in stating that the closed coil end of the valve spring should be positioned against the cylinder head. This end is typically ground flat to provide a stable seating surface, ensuring proper spring alignment and function.

Technician B is incorrect in claiming that all valve springs use shims to adjust free spring height. In reality, shims are sometimes used to achieve the correct assembled height, which is the distance between the spring seat and the retainer when the valve is closed. Not all valve springs require shims, and the term free spring height refers to the uncompressed length of the spring—not the installed dimension. Therefore, Technician B’s statement is both inaccurate and based on incorrect terminology.

If coolant is leaking and a radiator pressure tester shows a rapid rise to 19 psi shortly after starting the engine, it’s a strong indication of a leaking cylinder head gasket.

The head gasket seals the combustion chamber and prevents coolant and oil from entering the cylinders or leaking out. When it fails, combustion gases can leak into the cooling system, increasing pressure beyond normal levels. For a cold engine, pressure should remain stable around 14–16 psi. A sudden rise to 19 psi suggests that exhaust gases are entering the cooling system, pushing the pressure higher.

While air pockets or acidic coolant can cause overheating and leaks, they do not cause a rapid pressure spike in a cold engine. Therefore, the abnormal pressure reading points to a head gasket failure. Symptoms may also include white exhaust smoke, overheating, and coolant loss.

Correct Answer: Rod Bearing

Rod bearing noise typically presents as a rhythmic thumping or knocking sound on the side of the engine block. It becomes louder as the engine heats up and usually disappears when the affected cylinder is shorted out.

Option A is incorrect because main bearing noise is constant and does not go away when a cylinder is shorted. Main bearing noise tends to be deeper in tone and produces a steady, evenly spaced single knock, unlike the more rapid double knock often associated with rod bearing failure.

Option B is also incorrect. Wrist pin noise can be identified by disconnecting spark plug wires one at a time. If the noise immediately doubles in frequency, it’s likely a wrist pin issue. If the noise merely lessens, it’s more likely a rod bearing problem.

Option D is incorrect because piston slap typically occurs when the engine is cold and disappears once it warms up. Piston slap may result from piston skirt deformation under load or wear.

Correct answer is: Perform a cooling system pressure test
The cooling system pressure test reveals the cause of the leak. It does this by pressurizing the cooling system just as it would if it were operating under normal conditions. There’s no need to visually look for the leaks prior to this test.

To diagnose a fully charged battery that discharges overnight, the most appropriate test is a parasitic drain test.

This test measures the amount of current being drawn from the battery when the vehicle is off and all accessories are shut down. If excessive current is detected, it may indicate that a component—such as an interior light or electronic module—is staying on and draining the battery.

Other tests are not suitable in this case:

• A specific gravity test checks the battery’s electrolyte condition but doesn’t reveal overnight discharge issues.

• A voltage drop test identifies charging or wiring problems but not parasitic drains.

• An alternator full-field test evaluates alternator output and also doesn’t diagnose battery drain while the vehicle is off.

If the flywheel’s ring gear teeth are worn, the ring gear can often be replaced without replacing the entire flywheel. This involves removing the old gear and installing a new one using the proper tools and techniques.

Minor scoring on the flywheel surface can be corrected through resurfacing, a machining process that restores a smooth, flat surface. This should be done by a qualified machine shop.

Therefore, both Technician A and Technician B are correct.

A clogged catalytic converter creates exhaust flow restriction, leading to a noticeable loss of power, especially during acceleration.

A clogged or faulty fuel injector can cause poor engine performance and misfires.

A worn outer CV joint typically produces a clicking or popping noise when turning slowly.

A damaged or broken engine or transmission mount often results in noticeable vibrations when the brake is applied and the transmission is in gear.

Correct Answer: Both A and B

Engine coolant contains corrosion inhibitors that gradually deplete, which is why it must be replaced and the system flushed at regular service intervals. However, its freeze-protection properties remain unchanged over time.

In an Electronic Throttle Control system, the return spring ensures the throttle valve closes when the accelerator pedal is released. If the spring fails or weakens, the valve may remain partially open.

A partially open throttle allows excess air into the engine, even without driver input. This disrupts the air-fuel ratio, causing a lean burn—a condition where combustion is incomplete, leading to reduced engine power.

Neither Technician A nor Technician B is correct.

A stuck open wastegate causes an under-boost condition, as the turbocharger cannot build sufficient pressure to force extra air into the engine. This results in power loss and may contribute to issues like engine overheating.

Conversely, a stuck closed wastegate leads to an over-boost condition. Exhaust gases can’t escape, causing excessive boost pressure, which can potentially damage the engine.

Correct Answer: Piston Slap

Piston slap is a knocking sound coming from the side of the engine, typically more noticeable when the engine is cold. As the engine warms up and components expand, the noise usually lessens or disappears.

Both Technician A and Technician B are correct.

Using a cylinder bore gauge to check for excessive taper is essential to ensure the bore hasn’t worn unevenly from top to bottom, which can affect piston ring sealing and reduce engine performance.

Checking for out-of-round conditions is equally important, as uneven circular wear can also compromise ring sealing and engine efficiency.

Therefore, both taper and out-of-round measurements are necessary to accurately assess cylinder bore condition before installing new pistons.

Correct Answer: Low Power

When DTC P1121 (Electric Throttle Control Actuator) is stored, the ECM activates fail-safe mode and illuminates the MIL. In this mode—specifically when malfunction A of P1121 is detected—the engine speed is limited to 2,000 RPM, resulting in a noticeable loss of power. During fail-safe operation, the ECM controls the throttle by maintaining its position near idle to protect the engine.

Worn piston rings allow engine oil to enter the combustion chamber, where it burns and leaves carbon deposits on the spark plug. This can lead to engine smoke, reduced performance, and power loss.

Technician A is correct in stating that a rich air-fuel ratio can lead to excessive carbon buildup on engine valves and pistons. When the mixture contains too much fuel, incomplete combustion occurs, allowing unburned fuel to deposit carbon and other residues on internal components. Over time, these deposits can reduce engine performance and increase emissions.

Technician B is incorrect in attributing significant carbon accumulation in the cylinders and piston crowns to coolant entering the combustion chamber. While coolant intrusion can cause serious issues—such as overheating, compression loss, and oil contamination—it does not directly result in carbon buildup. Instead, carbon deposits in these areas are typically caused by incomplete combustion due to a rich mixture, low-quality fuel, or poor maintenance practices like infrequent oil or air filter changes.

Conclusion: Technician A’s explanation is accurate, while Technician B’s reasoning about coolant causing carbon buildup is incorrect.

The most likely cause of a loud, whirling noise that increases with engine speed in a longitudinal engine is a faulty viscous fan clutch. This component controls the speed of the engine’s cooling fan. When it fails, the fan may spin excessively, creating a loud, whirling sound that rises with RPM.

While a cracked fan blade can cause noise, it typically results in a constant sound rather than one that varies with engine speed. A weak electric cooling fan motor may reduce airflow but is unlikely to produce a loud, whirling noise. A worn accessory belt might create a squeal or squeak, but not the distinctive whirling sound associated with a failing fan clutch.

Conclusion: The faulty viscous fan clutch is the most probable source of the noise.

Correct answer: Check for proper timing.
Sticking valves, weak valve springs, and exhaust restrictions can cause fluctuating vacuum readings. However, exhaust restrictions should be tested separately, typically by checking vacuum under acceleration rather than at idle.

Steps for Inspecting an Aluminum Cylinder Head

1. Clean the Cylinder Head
   Begin by thoroughly cleaning the cylinder head to remove any dirt, oil, or debris. A clean surface ensures accurate inspection and prevents contaminants from obscuring damage.

2. Visual Inspection
   Carefully examine the head for visible signs of cracks, damage, or warpage. Cracks may appear as fine lines or separations. To check for warpage, use a straightedge across the surface and look for any gaps.

3. Magnetic Particle Inspection (Not Applicable to Aluminum)
   Magnaflux, or Magnetic Particle Inspection (MPI), is a non-destructive test used to detect surface and near-surface cracks in ferromagnetic metals like iron or steel. However, aluminum is non-ferromagnetic and does not respond to magnetic fields, making MPI ineffective for aluminum cylinder heads.

4. Pressure Testing
   To detect internal leaks, perform a pressure test by sealing the coolant passages and applying pressure to the cooling system. A pressure drop indicates a leak, which could point to a hidden crack or casting defect.

5. Machining if Warped
   If warpage is found, the cylinder head may require resurfacing. This involves carefully machining the head surface to restore flatness and ensure a proper seal with the engine block.

Conclusion:
When inspecting an aluminum cylinder head, technicians should rely on visual inspection, pressure testing, and surface flatness checks. Since MPI is ineffective on aluminum, alternative methods must be used to accurately detect cracks or defects and determine whether repair or replacement is necessary

Disabling the fuel injection and ignition systems during a compression test is not done to improve accuracy, but to ensure safety and prevent equipment damage.

If these systems remain active, fuel may be injected into the cylinders while the engine is cranked. Combined with spark from the ignition system, this poses a serious fire hazard. Additionally, the ignition system can be damaged if it fires with no fuel-air mixture to ignite, as the spark has nowhere to discharge safely.

By disabling both systems, the compression test can be performed safely and without risk to the vehicle’s components.

During a power balance test, the technician checks whether all cylinders are producing equal power by disabling each cylinder one at a time while the engine runs at a constant speed. The resulting drop in RPM is measured—typically with a tachometer—to determine the power contribution of each cylinder. A smaller RPM drop may indicate a weak or non-functioning cylinder.

Technician A is correct in emphasizing the importance of recording engine RPM before and during each cylinder test. Monitoring these values ensures consistent engine speed, which is essential for accurate and reliable results.

Correct answer: Inspect the pulleys for signs of excess play or bearing noise.
A rattling sound is most likely caused by a loose pulley or a failing bearing within the pulley. The drive belt itself typically does not produce a rattling noise. It’s important to identify the faulty component before replacing any parts.

A swollen oil filter is typically caused by excessive internal pressure, which may result from several factors:

1. Dirty or Contaminated Oil: Sludge or debris can clog the filter, restricting flow and increasing pressure inside the filter housing.

2. Faulty Oil Pressure Relief Valve: This valve regulates engine oil pressure. If it malfunctions, pressure can rise unchecked, causing the filter to swell.

3. Incorrect Oil Filter: Using the wrong filter may result in a poor fit or insufficient pressure tolerance, leading to deformation under normal operating conditions.

While worn crankshaft bearings can reduce oil pressure and harm the engine, they are not a direct cause of filter swelling.

If an oil filter appears swollen—especially during an oil change—it likely indicates a malfunctioning oil system or an incompatible filter. The filter should be replaced immediately, and the underlying issue addressed to prevent engine damage.

A wet compression test involves adding a small amount of oil to the cylinder before measuring compression. The oil helps seal worn piston rings temporarily, which can reveal whether low compression is caused by ring wear or another issue.

If piston rings are worn, compression should increase after adding oil. However, if compression remains low, the problem likely lies elsewhere—such as leaking intake or exhaust valves. Faulty valves can allow pressure to escape from the combustion chamber, and since oil doesn’t seal valve leaks, the compression reading would stay the same.

A leaking head gasket is the most common cause of white exhaust smoke at all engine speeds. The head gasket seals the joint between the engine block and cylinder head, keeping oil and coolant passages separate. If it fails, coolant can enter the combustion chamber and burn with the air-fuel mixture, producing white-colored exhaust from the tailpipe.

While a leaking fuel injector can also cause white smoke, it usually occurs only at idle or low speeds, when unburnt fuel is expelled due to incomplete combustion.

In contrast, worn piston rings or valve seals typically cause blue smoke, indicating that oil is entering and burning in the combustion chamber. White exhaust is more closely linked to coolant contamination, most often from a failed head gasket.

Checking if all fuel injectors have the same electrical resistance is a useful first step because:

• It’s simple and quick: Measuring resistance with a multimeter is easy and doesn’t require specialized tools.

• It allows for comparison: A significant difference in resistance between one injector and the others can indicate a problem, even if you don’t know the exact factory specifications.

Correct answer: Technician A
The closed coil end of a valve spring should be installed against the cylinder head. Valve springs do not rely on shims to control assembled height. Additionally, Technician B incorrectly referred to this as the “free spring height,” which is not relevant in this context.

Both Technician A and Technician B are correct.

Technician A is correct in stating that oil viscosity changes with engine temperature. When the engine is cold, oil is thicker, providing added protection. As the engine warms up, the oil becomes thinner, allowing it to circulate more easily and lubricate moving parts effectively.

Technician B is also correct in stating that a defective oil cooler can cause a coolant leak. The oil cooler helps control oil temperature by transferring heat to the coolant. If it fails or develops a leak, coolant and oil can mix, potentially leading to engine damage and reduced performance.

Conclusion: Both technicians are accurate in their explanations, highlighting the importance of monitoring both the engine’s oil and cooling systems for optimal performance and reliability.