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Questions and Answers
What can be the possible cause of an air-fuel ratio (very rich) of 10.1 at all speeds?
What else can cause a rich air-fuel ratio (10.1 to 12.1) at low speed?
What else could cause an air-fuel ratio very lean (above 16.1) at all speeds?
What can cause an air-fuel ratio very lean (above 16.1) at high speed?
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What is the cause of normal 13.1 to 15.1 emission readings?
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What is the condition if HC shows moderate increase, CO shows large increase, CO2 shows some decrease, O2 shows some decrease, and NOx shows some decrease?
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What can cause higher emissions for NOx?
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What can cause HC to show a large increase, CO to show a large decrease, CO2 to show some decrease, O2 to show a large increase, and NOx to show a large increase?
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What is the condition if HC shows a large increase, CO shows some decrease, CO2 shows some decrease, O2 shows moderate increase, and NOx shows moderate decrease?
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What condition matches an increase in HC, decrease in CO, no change in CO2, decrease in O2, and large increase in NOx?
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What causes excessive blow by?
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Which of the following statements regarding composite engine OBD2 monitoring is false?
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What should a vehicle data link resistance measure at the DLC terminal?
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If there is no physical misfire but a misfire counter is current, what could that cause be?
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What does the MAP sensor read at idle under no load?
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What causes excessive contamination of the MAF sensor?
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If the TAC has only one sensor faulty, can throttle actuator control function but limited?
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If the throttle body actuators were disabled, what would the throttle position be?
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If normal throttle body percentage is 5-10% (850-950rpm), what is the percentage when one of the throttle position sensors fails?
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Can a coil blow/open a fuse if current is excessive?
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If a shorted driver is current, what would be damaged?
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A high IAC can be caused by:
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At idle, HC was acceptable but isn't under load. What could cause this?
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What can cause a misfire under load?
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What can help with ignition misfire?
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What can cause a hole in the distributor cap?
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Vacuum leaks will cause MAP vacuum readings to be?
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A kink in the fuel pressure regulator vacuum hose will cause?
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IAC regulates bypass air when the throttle body is closed. When the valve is fully extended, what needs to be done in order to START the vehicle?
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Vehicle overheating will cause?
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Technician A says that most immobilizer systems will turn off the fuel injectors if there is a fault in the anti-theft system. Technician B says that the ignition system is also disabled. Who is correct?
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Why does the immobilizer system only disable the fuel injectors when a fault in the anti-theft system is present?
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The composite vehicle engine speed will not rise above 6000 rpm. This is most likely due to:
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A restricted exhaust will limit rpm well below?
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If the IAT is reading -10° (4.5V) and the ECT is reading 212 degrees F, what can cause poor fuel economy?
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A DTC P0102 - MAF sensor low voltage could be caused by all of the following EXCEPT:
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A water intrusion will cause a higher MAF signal voltage resulting in?
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When does the Variable Valve Timing turn on?
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When does the fuel cut off occur?
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When does the Torque Converter apply?
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This vehicle uses what sensor for aid in A/F ratio?
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What's a large leak test?
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If the transmission was in fail-safe mode, will the TC apply?
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Technician A says a cracked spark plug will cause firing voltage to increase. Technician B says that a fouled spark plug will also cause firing voltage to increase. Who is correct?
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If EGR temp is close to Engine coolant temp, what can this indicate?
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If EGR is much higher than ECT, what can this indicate?
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Spark knock can be caused by which of the following?
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A smaller spark plug gap will cause?
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Study Notes
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.
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Description
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!
