ASE L1 Engine Performance Flashcards

Air-Fuel Ratio and Emissions

• Very rich air-fuel ratio (10.1) at all speeds shows high HC (up to 300ppm), CO (3%), CO2 (7-9%), and low O2 (0.2%). Possible causes include leaking injectors, high MAP sensor voltage, or stuck open thermostat.
• Rich air-fuel ratio (10.1 to 12.1) leads to moderate HC (100-150ppm), stable CO (1.5%), increased CO2 (up to 13%), and O2 (up to 1.0%). Causes may include low fuel pressure or a bad camshaft.
• Very lean air-fuel ratio (above 16.1) results in moderate HC (200-250ppm), low CO (0.5-1.0%), stable CO2 (7-9%), and high O2 (4-5%). Potential causes are intermittent ignition problems, restricted fuel injectors, or improper timing.
• Normal emission levels (13.1 to 15.1) indicate ideal operation: low HC (50-100ppm), minimal CO (0.3%), CO2 (10-12%), and stable O2 (2.5%). A cause for these readings could be the engine temperature being too cold.

Emission Patterns and Conditions

• Increase in HC with large CO decrease and some CO2 decrease indicates a lean mixture situation.
• Increase in emissions of NOx can be attributed to advanced timing, a stuck closed EGR valve, or cooling system issues.
• High HC and CO with large NOx increase points to very lean mixture conditions.

Engine Performance Issues

• High MAP voltages under no load typically indicate vacuum leaks.
• Low fuel pressures generally lead to high CO emissions.
• Injector leakage can cause rough idle, black smoke, or vacuum leaks, while a malfunctioning PCV can lead to excessive blow-by but not elevated MIL indications.

Diagnostic Trouble Codes and ECU Monitoring

• Communication faults in a vehicle's CAN could be due to shorted harness.
• A P0341 code suggests camshaft position sensor issues, possibly linked to excessive camshaft end-play.
• Injector issues like leaking O-rings can raise emissions and affect performance without obvious symptoms.

Engine Management Functions

• High IAC values may arise from throttle body contamination, clogged passages, or faulty IAC units.
• MAP sensor operates at about 1.28V under idle conditions with no load.
• Engine temperature sensor readings should decrease as the engine heats, signaling appropriate performance.

General Emission Regulations

• Oxygen (O2) and carbon monoxide (CO) emissions can feature high readings simultaneously in certain fault conditions.
• Failure of diagnostic monitors during emissions testing can indicate incomplete readiness or failures of associated O2 sensors.
• Spark knocks can be caused by excessive scaling in the cooling system and can be improved by using appropriate fuel octanes.

Fuel and Air Management

• A malfunctioning IAC valve can prevent engine start if it remains fully extended.
• Clogged fuel injectors lead to decreased CO2 readings and increased CO emissions, suggesting an urgent need for maintenance.
• Efficient diagnostic testing includes observing fuel trims and O2 readings for accurate fault resolution.

Key Effects of Sensor Operation on Engine Performance

• High throttle position values from faulty sensors can lead to abnormal engine operation conditions, including hard starting.
• A waste spark ignition system tests indicate that crankshaft and camshaft sensors need to be checked for integrity.

Additional Notes

• Be aware of potential ignition misfires caused by worn or fouled spark plugs, which can escalate under load conditions.
• Vacuum leaks significantly influence MAP sensor readings, underscoring the need for a system-wide pressure check during diagnostics.### Engine Performance and Diagnostics
• Vehicle overheating leads to high hydrocarbon (HC) and carbon monoxide (CO) levels.
• Immobilizer systems disable fuel injectors during faults in the anti-theft system to prevent high HC emissions.
• A composite vehicle engine speed limit of 6000 rpm can be attributed to ECM programming.

Exhaust and Emission Controls

• Restricted exhaust impacts engine performance, limiting rpm below 6000.
• Water intrusion into the MAF sensor causes a rich condition due to elevated signal voltage.

Sensor Function and Fuel Economy

• A faulty intake air temperature (IAT) sensor can result in poor fuel economy.
• A common diagnostic trouble code (DTC) P0102 indicates low MAF sensor voltage, often due to clogged exhaust or air duct leaks, but not water intrusion.

Variable Valve Timing and Fuel Cut-Off

• Variable valve timing engages around 3000 rpm to optimize performance.
• Fuel cut-off occurs at 6000 rpm and under specific conditions such as deceleration and temperature thresholds.

Torque Converter and Transmission Behavior

• The torque converter engages above 35 mph, in third gear or higher, and when engine temperature exceeds 150°F.
• In fail-safe mode, the torque converter will not apply.

Spark Plug and EGR Functionality

• Cracked or fouled spark plugs do not increase firing voltage; both technicians are incorrect.
• Matching temperatures between the EGR and engine coolant suggest insufficient EGR flow, while higher EGR temperatures may indicate overheating issues.

Emission and Spark Conditions

• Spark knock can arise from using hotter-than-specified spark plugs, while a smaller spark plug gap potentially increases HC emissions.

Test your knowledge on engine performance with these ASE L1 flashcards. Each card challenges you to identify causes of air fuel ratio issues and understand key performance metrics at various speeds. Get ready to enhance your automotive expertise!