MTTC Automotive Trade Test flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Stoichiometric air-fuel ratio
- The mass ratio of air to fuel that burns completely with no excess oxygen or fuel; for gasoline it is about 14.7 to 1.
- Leak-down test
- Pressurized air is applied to a cylinder at top dead center and the percentage lost is measured to locate ring, valve, or head gasket leakage.
- Long-term fuel trim
- The PCM's learned correction to fuel delivery; positive values add fuel for a lean condition and negative values remove fuel for a rich condition.
- Torque-to-yield bolt
- A head or main bolt tightened past its elastic limit using a torque plus angle sequence; it stretches permanently and must be replaced each time.
- Compression ratio
- The ratio of cylinder volume at bottom dead center to volume at top dead center, calculated as swept volume plus clearance volume divided by clearance volume.
- Clutch slippage
- Engine speed rises without matching vehicle speed under load, indicating a worn friction disc, weak pressure plate, or incorrect release bearing clearance.
- Torque converter lockup
- A clutch inside the converter mechanically couples the turbine to the impeller at cruise, eliminating slip and improving fuel economy.
- Continuously variable transmission
- A transmission using a steel belt or chain between variable-diameter pulleys to provide an infinite range of ratios and requiring its own specified fluid.
- Shift solenoid
- An electrically controlled valve in an automatic transmission that directs hydraulic pressure to engage or release clutches and bands for each gear.
- Overall gear ratio
- The transmission gear ratio multiplied by the final drive ratio; it determines engine speed relative to wheel speed in a given gear.
- Caster angle
- The forward or backward tilt of the steering axis viewed from the side; positive caster improves straight-line stability and steering return.
- Included angle
- The sum of camber and the steering axis inclination; it changes when the knuckle or strut is bent, unlike camber alone.
- Thrust angle
- The average rear toe angle relative to the vehicle centerline; a nonzero value causes the vehicle to dog-track and the steering wheel to be off center.
- Toe setting
- The difference in track width measured at the front and rear of the tires; toe-in stabilizes the vehicle and toe-out quickens turn-in.
- Tire cupping
- A scalloped wear pattern caused by worn shocks or struts that allow the tire to bounce and lose contact with the road.
- Brake fluid hygroscopy
- Glycol-based DOT 3 and DOT 4 fluids absorb moisture from the air, lowering their boiling point and requiring periodic replacement.
- Brake fade
- Loss of braking force when heat from repeated stops exceeds the friction material's temperature limit or boils the brake fluid.
- ABS wheel speed sensor
- A sensor at each wheel that reports rotational speed to the ABS module, which modulates brake pressure to prevent wheel lockup during hard stops.
- Rotor minimum thickness
- The manufacturer's smallest allowable disc thickness, stamped on the rotor; machining or wear below this value requires rotor replacement.
- Ohm's law
- Voltage equals current multiplied by resistance; combined with power equals voltage times current, it is the basis for circuit diagnosis.
- Voltage drop test
- Measuring voltage lost across a connection or cable while current flows; excessive drop indicates high resistance from corrosion or loose terminals.
- Parallel circuit
- A circuit in which branches share the same voltage and current divides among them, so total resistance is less than the smallest branch.
- CAN bus
- A twisted-pair differential network that lets control modules exchange data; a short or open on the bus disables communication across many systems.
- Alternator AC ripple
- Alternating current leaking past a failed rectifier diode, causing flickering lights and erratic charging that a multimeter set to AC can detect.
- Subcooling
- Condensing temperature minus condenser outlet temperature; low subcooling indicates an undercharged system or a condenser problem.
- Superheat
- Evaporator outlet temperature minus evaporating temperature; high superheat suggests low refrigerant charge or a restricted expansion device.
- Blend door actuator
- A motor that moves a door mixing air through the heater core and evaporator to control outlet temperature; failure causes one-temperature output.
- Refrigeration cycle order
- Refrigerant flows from compressor to condenser to expansion device to evaporator and returns to the compressor, absorbing heat in the evaporator.
- Micrometer use
- A precision measuring tool with a calibrated thimble read to 0.0001 inch, used for brake rotors, bearing journals, and shim thickness.
- Plastigauge
- A crushable plastic strip placed on a bearing journal; its flattened width after torqueing indicates oil clearance for connecting rod or main bearings.
- Formative assessment
- Ongoing checks of student understanding during instruction, such as questioning or lab observation, used to adjust teaching before final evaluation.
- Hazard communication
- The requirement that chemical hazards be communicated through labels, safety data sheets, and employee training before use in the workplace.