MITO Light Auto L4 cheat sheet

Four-stroke cycle: intake, compression, power and exhaust; the crankshaft rotates two turns (720°) per complete cycle and each cylinder fires once per cycle.

Petrol stoichiometric air-fuel ratio is about 14.7:1 by mass; diesel stoichiometric is about 14.5:1, although diesel engines normally run lean.

Displacement per cylinder = π/4 × bore² × stroke; total engine displacement = that value × number of cylinders, with bore and stroke in the same units.

Compression ratio = (swept volume + clearance volume) ÷ clearance volume; a higher ratio raises thermal efficiency but can promote knock.

Brake power (kW) = torque (N·m) × engine speed (rpm) ÷ 9549; torque is turning effort and power is the rate of doing work.

Overall drivetrain ratio = gearbox ratio × final drive ratio; a higher numerical overall ratio multiplies torque at the wheels and reduces road speed for a given engine speed.

Timing belt alignment marks on the crankshaft, camshaft and belt must align exactly; on an interference engine, incorrect timing can cause valve-to-piston contact.

A clicking noise that rises with steering lock during turns commonly indicates a worn outer CV joint; vibration under acceleration in a straight line more often indicates an inner CV joint or driveshaft imbalance.

Valve clearance outside specification: too tight can hold a valve off its seat and cause compression loss or burnt valves; too loose causes noise and accelerated valvetrain wear.

Ohm's law: V = I × R; electrical power P = V × I = I² × R = V² ÷ R, with consistent units.

Series resistances add and current is common; for parallel resistances, 1/Rt = 1/R1 + 1/R2 + … and total resistance is less than the smallest branch.

A 12 V lead-acid battery has six cells at about 2.1 V each; a rested, fully charged open-circuit voltage is approximately 12.6–12.8 V, and about 12.2 V indicates roughly 50% state of charge.

Alternator charging voltage is typically 13.8–14.7 V at 20°C with loads off; sustained voltage below about 13.2 V indicates undercharging or excessive load.

Relay pins: 30 is the common power feed, 87 is normally open output, 87a is normally closed output, and 85/86 are the coil.

A healthy CAN bus usually measures about 60 Ω across CAN high and CAN low with the battery disconnected, because two 120 Ω terminating resistors are in parallel.

Parasitic draw is measured in series with the battery after modules sleep; a typical acceptable value is below 50 mA (0.05 A), with many vehicles drawing 20–30 mA.

Voltage drop testing: with the circuit loaded, a good cable or connection generally drops less than 0.5 V; a ground circuit should typically drop less than 0.2 V.

Diode forward voltage drop is typically 0.5–0.7 V for a silicon diode; a reading of OL in both directions indicates an open diode.

Positive caster places the top of the steering axis rearward; it increases straight-line stability and self-centring, but excessive positive caster increases steering effort.

Negative camber tilts the top of the wheel inward; it increases cornering grip but wears the tyre inner edge, while positive camber wears the outer edge.

Included angle = steering axis inclination (SAI) + camber; comparing left and right helps identify a bent strut, knuckle or suspension component.

Hydraulic pressure P = F/A; for the same pedal force, a smaller master-cylinder piston raises pressure, and a larger caliper piston raises clamping force.

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

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

Alignment sequence: set rear camber and toe first, then front camber and caster, then front toe; a steering angle sensor reset may be required afterwards.

A brake disc below minimum thickness, or with runout above specification, must be replaced; resurfacing is permitted only if final thickness remains above minimum.

Worn suspension ball joints are checked with the suspension loaded and the wheel raised via the lower control arm; play beyond specification requires replacement.

Torque = force × perpendicular lever length; torque is measured in newton metres (N·m), and 1 kgf·m ≈ 9.81 N·m.

A torque wrench is generally accurate from 20% to 100% of its scale; selecting a wrench that places the target torque mid-range improves accuracy.

Torque-to-yield bolts are tightened to a specified torque plus a rotational angle; they permanently stretch and are normally single-use.

Micrometer reading = barrel whole millimetres + thimble hundredths; check zero with the anvils closed and clean before use.

Plastigauge is compressed across a bearing journal and its flattened width is compared with a scale to determine bearing clearance.

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

Wheel nuts are tightened in a star or diagonal sequence to the specified torque; overtightening can distort brake discs and stretch studs.

Used engine oil, brake fluid and coolant are segregated and sent for recycling or approved disposal; brake fluid must not be mixed with oil.

A job record should include VIN, odometer, complaint, measurements, parts used, labour and final road test result.

OBD-II DLC: pins 4 and 5 are chassis and signal ground, pin 16 is battery positive, pins 6 and 14 are CAN high and low, and pins 7 and 15 are ISO 9141/ISO 14230 K-line and L-line.

A scan tool's freeze frame records operating conditions when a DTC set; live data should be compared with expected values under the same conditions.

Voltmeter in parallel, ammeter in series, ohmmeter on an unpowered circuit; a voltage drop test is made under load.

Compression test: engine at operating temperature, all spark plugs removed, throttle wide open, four to six strokes per cylinder; readings should be within about 10% of each other.

Cylinder leakage test: bring the cylinder to TDC on compression, apply regulated air, and listen at the intake, exhaust, oil filler and radiator for the leak path.

A vacuum gauge that reads low and steady can indicate intake leakage, late valve timing or low compression; a fluctuating needle can indicate a valve or ignition fault.

Oscilloscope testing shows signal shape and time; an ignition coil primary waveform should show a clean dwell, firing line and burn time.

Diagnostic sequence: verify the complaint, check for DTCs and freeze frame, inspect visually, test the circuit, repair, then verify the repair under the original conditions.

Fuel pressure test: connect a gauge to the test port, compare running and key-on engine-off pressures with specification, and check for pressure drop after shutdown.

PPE for workshop tasks includes safety glasses, hearing protection, gloves, safety footwear and, where required, respiratory protection.

Never work under a vehicle supported only by a hydraulic jack; use rated jack stands on a hard, level surface.

Carbon monoxide from engine exhaust is colourless and odourless; run engines only with exhaust extraction or adequate ventilation.

Fire classes: A solids, B flammable liquids, C flammable gases, E energised electrical, F cooking oils; use CO2 or dry chemical on electrical fires.

A safety data sheet (SDS) gives hazard, handling, storage, first-aid and disposal information; it must be accessible for every hazardous chemical used.

Before electric welding, disconnect the battery and unplug sensitive electronic modules to prevent current flow and voltage spikes damaging them.

Manual handling: keep the load close, bend the knees, avoid twisting, and use a team lift or mechanical aid for heavy or awkward loads.

All workplace incidents, near misses and hazards must be reported and recorded under the site's health and safety system.

A residual current device (RCD) protects portable electrical tools by tripping on earth leakage; test it before use and never bypass it.