MITO Light Auto L4 flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Four-stroke cycle order

Intake, compression, power and exhaust strokes occur in that order; the crankshaft turns two full revolutions per cycle, and each cylinder produces one power stroke per 720 degrees.

Stoichiometric petrol air-fuel ratio

For petrol, the chemically correct mass ratio is about 14.7 parts air to 1 part fuel; richer mixtures add fuel, and leaner mixtures add air.

Compression ratio formula

Compression ratio equals swept volume plus clearance volume, divided by clearance volume; it is a volume ratio and does not directly state cylinder pressure.

Overall drivetrain ratio

Overall ratio equals gearbox ratio multiplied by final drive ratio; a higher numerical overall ratio increases torque at the wheels and lowers road speed at a given engine speed.

Interference engine timing belt

In an interference engine, valve and piston paths overlap, so a broken or jumped timing belt can cause valve and piston damage; timing marks must align exactly.

Ohm's law

Voltage equals current multiplied by resistance, written V = I × R; if two values are known, the third can be calculated for a resistive circuit.

Parallel resistance rule

For resistors in parallel, the reciprocal of total resistance equals the sum of the reciprocals of each branch; total resistance is always less than the smallest branch resistance.

Relay terminals 30 and 87

Terminal 30 is the common power feed and terminal 87 is the normally open output; terminals 85 and 86 are the coil, which connects 30 to 87 when energised.

CAN bus termination resistance

A healthy CAN bus usually measures about 60 ohms between CAN high and CAN low with the battery disconnected, because two 120-ohm terminating resistors are connected in parallel.

Parasitic current draw limit

After control modules have slept, a typical vehicle parasitic draw is below 50 milliamps; a higher reading can flatten the battery and is traced by isolating circuits.

Charging voltage specification

With the engine running and electrical loads off, alternator output is commonly 13.8 to 14.7 volts at room temperature; sustained voltage below about 13.2 volts suggests undercharging.

Positive caster effect

Positive caster places the top of the steering axis rearward, which improves straight-line stability and steering self-centring; excessive caster increases steering effort and tyre wear.

Negative camber effect

Negative camber tilts the top of the wheel inward, improving cornering grip but concentrating tyre wear on the inner edge; excessive negative camber reduces straight-line traction.

Included angle formula

Included angle equals steering axis inclination plus camber; comparing it side to side helps identify a bent strut, knuckle or suspension component.

Brake hydraulic pressure formula

Hydraulic pressure equals force divided by piston area (P = F/A); a smaller master-cylinder piston raises pressure for a given pedal force, and a larger caliper piston increases clamping force.

DOT 4 brake fluid moisture

DOT 4 brake fluid is hygroscopic, so absorbed moisture lowers its boiling point and increases vapour-lock risk under heavy braking; it is replaced at the specified service interval.

Rear thrust angle

Thrust angle is the angle between the vehicle's geometric centreline and the rear axle centreline; unequal rear toe creates a non-zero thrust angle and causes dog-tracking.

Torque wrench accuracy range

A torque wrench is generally accurate from 20 to 100 percent of its scale; choosing a wrench where the target torque falls mid-range improves accuracy.

Torque-to-yield bolt

A torque-to-yield bolt is tightened to a specified torque and then rotated through a set angle; it stretches permanently and is normally not reusable.

Micrometer reading method

Read whole millimetres from the barrel scale, add hundredths from the thimble scale, and check zero with the anvils closed and clean before measuring.

Plastigauge bearing clearance

Plastigauge is placed across a bearing journal, the cap is torqued, and the flattened strip width is compared with a scale to determine bearing clearance.

Cylinder head bolt sequence

Cylinder head bolts are tightened in the manufacturer's sequence, usually from the centre outward in stages, to distribute clamping load and prevent head distortion.

OBD-II DLC power pins

On a standard OBD-II connector, pins 4 and 5 are chassis and signal grounds, pin 16 is battery positive, and pins 6 and 14 are CAN high and low.

Voltmeter and ammeter connection

A voltmeter is connected in parallel with the circuit, an ammeter in series, and an ohmmeter across an unpowered circuit; incorrect connection can damage the meter or circuit.

Compression test procedure

Remove all spark plugs, hold the throttle wide open, crank four to six strokes per cylinder, and compare readings; cylinders should usually be within about 10 percent.

Cylinder leakage test

Apply regulated air to a cylinder at top dead centre and listen at the intake, exhaust, oil filler and radiator to locate leaking valves, rings or head gasket.

Freeze frame data

Freeze frame stores operating conditions such as engine speed, load and coolant temperature when a diagnostic trouble code was set, helping reproduce the fault.

Jack stand support rule

A vehicle must be supported on rated jack stands on a hard level surface before any part of the body goes underneath; a hydraulic jack alone is not acceptable.

Carbon monoxide hazard

Engine exhaust contains carbon monoxide, which is colourless and odourless; engines must not run in an enclosed workshop without effective exhaust extraction.

Electrical fire extinguisher class

Class E fires involve energised electrical equipment; use a carbon dioxide or dry chemical extinguisher and isolate the power first if it is safe.

Safety data sheet

A safety data sheet provides hazard, handling, storage, first-aid and disposal information for a chemical; it must be readily accessible to workers who use the product.

Battery disconnect before welding

Disconnect the battery and unplug sensitive electronic control modules before electric welding on a vehicle to prevent current flow and voltage spikes damaging modules.