Advanced Engine Performance Specialist Flashcards

The EGR (Exhaust Gas Recirculation) valve may be closed, according to a technician. A closed EGR valve would be indicated by which of the following?

Answer: Spark knock

The EGR system recirculates exhaust gases to lower combustion temperatures. If the EGR valve is closed, it prevents this cooling effect, leading to higher cylinder temperatures. These elevated temperatures can cause the air-fuel mixture to ignite prematurely, resulting in uncontrolled combustion known as spark knock or detonation.

What is the LEAST likely reason of a gasoline tank leak:

Answer: defective tank straps.

Defective tank straps are designed to hold the fuel tank securely in place, not to contain fuel. While they could indirectly lead to damage if the tank becomes loose, the straps themselves do not cause a leak from the tank's sealed structure. Corrosion, defective seams, and road damage directly compromise the tank material, leading to fuel leaks.

Blue smoke comes from the exhaust pipe of a vehicle. Technician X says that blocked cylinder head oil return passages could be the cause. Technician Y says that a stuck-open engine thermostat could be the cause. Who is right?

Answer: X only

Blue smoke from the exhaust indicates that engine oil is being burned. Blocked cylinder head oil return passages can cause oil to accumulate in the cylinder head, allowing it to seep past valve seals or guides into the combustion chamber. A stuck-open engine thermostat would cause the engine to run cold, affecting fuel economy and emissions, but not directly causing oil to burn.

What should you do first when diagnosing an engine performance problem?

Answer: Discuss the concern with the owner of the vehicle

The initial and most crucial step in diagnosing any vehicle problem is to thoroughly understand the customer's complaint. Discussing the concern with the owner provides vital information about the symptoms, when they occur, and under what conditions, which helps guide the entire diagnostic process. This ensures the technician addresses the actual problem the customer is experiencing.

The plastic sensors on an electronically controlled EGR valve have melted. Technician X says excessive back pressure caused by a partially clogged exhaust system could be the cause. Technician Y says to always check for a restricted exhaust whenever replacing a failed EGR valve sensor. Who is right?

Answer: Both X and Y

Both technicians are correct. Excessive exhaust back pressure, often caused by a restricted exhaust system, can force hot exhaust gases back into the EGR valve, leading to overheating and melting of its plastic components. Therefore, when replacing a failed EGR valve, it is crucial to check for exhaust restrictions to prevent a recurrence of the problem, as Technician Y suggests.

All of these reduce the life of the turbocharger, except:

Answer: exhaust system damage.

A turbocharger's life is primarily affected by factors related to lubrication, cooling, and the quality of air entering it. Lack of air cleaner maintenance allows debris to damage the compressor, insufficient oil changes lead to bearing wear, and inadequate cooling causes heat damage. While severe exhaust system damage could affect performance, it doesn't directly reduce the turbocharger's internal component life in the same fundamental way as issues with air, oil, or cooling.

A vehicle is being diagnosed for poor fuel economy. Engine tests show a rich exhaust gas mixture. Technician X says that a failed oxygen (O2 ) sensor could be the cause. Technician Y says that a failed engine coolant temperature sensor could be the cause. Who is right?

Answer: Both X and Y

Both technicians are correct. A rich exhaust gas mixture indicates an excess of fuel. A failed oxygen (O2) sensor can send an inaccurate signal to the engine control module (ECM), causing it to command more fuel than necessary. Similarly, a failed engine coolant temperature sensor might incorrectly report a cold engine, prompting the ECM to enrich the fuel mixture for warm-up, even if the engine is already warm, leading to a rich condition.

Technician X believes that paper service manuals still get used today. Technician Y believes that you should always follow recommended service procedures found in online service information. Who is correct?

Answer: Technician Y

Technician Y is correct because modern automotive repair relies heavily on up-to-date online service information. These digital resources provide the most current procedures, technical service bulletins (TSBs), and diagnostic information, which are essential for accurate and efficient repairs on contemporary vehicles. While some paper manuals may still exist, online resources are the industry standard for comprehensive and current data.

A disconnected spark plug is interpreted by the vehicle's OBD II (On Board Diagnostic Level 2) system as a misfire that could harm the three-way catalyst. On which trip will the Malfunction Indicator Lamp (MIL) be most likely turned on by the ECM or PCM?

Answer: 1st trip

A misfire condition, especially one severe enough to potentially harm the catalytic converter (a Type A or Category 1 fault), is considered critical by OBD II standards. For such severe faults, the Malfunction Indicator Lamp (MIL) is illuminated on the *first* driving cycle in which the fault is detected. This immediate alert is crucial to prevent further damage to expensive emission control components.

The following below are true about the cylinder leakage test. Except:

Answer: a gauge reading of 100 percent indicates no cylinder leakage.

A cylinder leakage test measures the percentage of air escaping from a cylinder. A gauge reading of 0 percent indicates no leakage, meaning the cylinder holds pressure perfectly. Conversely, a reading of 100 percent would indicate complete leakage, meaning all the air is escaping, which is the opposite of no leakage. Therefore, stating 100 percent indicates no leakage is incorrect.

An engine's intake manifold is connected to a vacuum gauge. The pointer on the gauge fluctuates rapidly between 10 and 22 in.Hg when the engine is running at 2,000 rpm. The cause could be:

Answer: a broken valve spring

Rapid and wide fluctuations in vacuum gauge readings at a steady RPM (like 2,000 rpm) typically indicate an intermittent or inconsistent cylinder sealing issue. A broken valve spring would prevent the valve from closing properly and consistently, leading to a loss of compression and varying vacuum levels as the engine runs, causing the gauge needle to fluctuate erratically.

What data do you need to know when looking for vehicle information for a given customer?

Answer: Make, model and year

To accurately look up vehicle-specific information in service manuals or online databases, the fundamental details required are the vehicle's make, model, and year. This combination allows technicians to identify the correct specifications, procedures, and parts for a particular vehicle. While a VIN is more precise, make, model, and year are the primary initial identifiers for general information retrieval.

Technician X says the on-board self-diagnostics test mode procedures should be conducted on a cold engine. Technician Y says many diagnostic trouble codes (DTC) will monitor items only when the engine control system is in closed loop. Who is right?

Answer: Y only

Technician Y is correct because many diagnostic trouble codes (DTCs) and self-diagnostics tests require the engine control system to be in 'closed loop' operation. Closed loop occurs when the engine reaches operating temperature and the oxygen sensors provide feedback for precise fuel control. Technician X is incorrect, as many tests specifically require a warm engine for accurate monitoring.

Exhaust manifold testing entails all of the following. Except:

Answer: checking for restricted exhaust manifold.

Exhaust manifold testing primarily involves inspecting its physical condition for cracks, warpage, and ensuring clean mating surfaces for proper sealing. While a restricted exhaust *system* can be a diagnostic concern, the exhaust manifold itself is generally not checked for restriction in the same way a catalytic converter or muffler would be. Its primary function is to collect exhaust gases, and restriction within the manifold itself is less common than issues like cracks or warpage.

On a vehicle that won't start, the technician discovers no spark and no injector pulses. It's possible that the cause is a failure:

Answer: crankshaft position (CKP) sensor

The crankshaft position (CKP) sensor is vital as it provides the ECM/PCM with engine speed and piston position information. This data is essential for timing both spark delivery and fuel injector pulses. If the CKP sensor fails, the ECM/PCM cannot accurately determine when to fire the spark plugs or open the injectors, resulting in a no-spark and no-injector-pulse condition, preventing the engine from starting.

When using a diagnostic strategy to investigate a drivability issue, which of these actions should come last in the process?

Answer: Verify repair

A standard diagnostic strategy follows a logical sequence: understanding the concern, performing initial checks, diagnosing the root cause, repairing the issue, and finally, verifying that the repair has resolved the original problem. Verifying the repair is the ultimate step to ensure the customer's concern is addressed and the vehicle is functioning correctly before returning it.

What component does the PCM or ECM monitor to assess the catalytic converter's status and, if it fails, set a DTC (Diagnostic Trouble Code)?

Answer: Front and rear O2 (oxygen) sensors

The PCM or ECM monitors the catalytic converter's efficiency by comparing the readings from the front (upstream) and rear (downstream) oxygen sensors. A properly functioning converter will show a significant difference in oxygen levels between the two sensors. If the rear sensor's readings mirror the front, it indicates the converter is not storing oxygen effectively, and a DTC will be set.

Replacement of an ignition module entails all of the following. Except:

Answer: dielectric silicone is used to seal the mating surface.

Dielectric silicone grease is used when replacing an ignition module primarily for heat dissipation, not for sealing. It helps transfer heat away from the module to the mounting surface (often a heat sink), preventing overheating and premature failure. Using it as a sealant is incorrect; its purpose is thermal conductivity to protect the module.

At idle, a return-type electronic fuel injection (EFI) system produces a lot of fuel pressure. Which of these possibly be the source of the problem?

Answer: Low manifold vacuum

In a return-type electronic fuel injection (EFI) system, the fuel pressure regulator is typically vacuum-referenced. High manifold vacuum (at idle) usually *reduces* fuel pressure to maintain a consistent pressure differential across the injectors. Conversely, low manifold vacuum (e.g., due to an engine problem or a disconnected vacuum line to the regulator) would cause the regulator to maintain a higher fuel pressure, leading to 'a lot of fuel pressure' at idle.

Which of the following is an unapproved method of obtaining DTC?

Answer: Cycling the malfunction indicator lamp on and off

Cycling the malfunction indicator lamp (MIL) on and off is not a recognized method for retrieving diagnostic trouble codes (DTCs). The MIL itself is an indicator light. Approved methods include using a scan tool, which is the most common and comprehensive, or in some older vehicles, specific ignition switch cycling procedures or connecting jumper wires to the data link connector (DLC) to flash codes.