Your FREE ASE T1 Flashcards 2026 – 200+ Cards

Intake, compression, power, exhaust — completed in two crankshaft revolutions per cylinder. Memory aid: Suck, Squeeze, Bang, Blow.

Measures cranking pressure per cylinder to judge how well rings, valves, and the head gasket seal. Readings should be within ~10% of each other.

Compression test repeated after adding oil to the cylinder. Reading rises = worn rings; stays low = valves or head gasket leak.

Applies compressed air to a cylinder at TDC and reads the percent leaking. Locates the leak by where air escapes (valves, rings, or head gasket).

Coolant entering the combustion chamber — usually a blown head gasket or cracked head. (Thin cold-start vapor is normal.)

Oil burning in the cylinder — worn piston rings, worn valve guides, or bad valve stem seals.

A rich air-fuel mixture — too much fuel or too little air (clogged air filter, leaking injector, faulty sensor).

Uncontrolled, spontaneous combustion AFTER the spark. Caused by low octane, too much advance, lean mixture, carbon, overheating, or high compression.

The mixture ignites BEFORE the spark, from a hot spot such as a glowing carbon deposit or hot spark plug.

Reads manifold vacuum at idle. Steady low = vacuum leak; fluctuating = burned valve; slowly dropping = restricted exhaust.

Disables one cylinder at a time and watches RPM. Little or no RPM drop = that cylinder is weak or dead.

The highest point of piston travel in the cylinder. Many tests and adjustments are made at TDC on the compression stroke.

The lowest point of piston travel in the cylinder, opposite TDC.

Combustion gases that slip past the piston rings into the crankcase. Excessive blow-by indicates worn rings or cylinders.

The three things every engine needs to run; a no-start diagnosis checks all three on the truck gasoline engine.

No-crank = the starter won't turn the engine (electrical/starter). No-start = it cranks but won't run (spark, fuel, or compression).

A cylinder failing to fire properly — from ignition, fuel, or compression loss. Causes rough idle, poor power, and a check-engine light.

An active misfire severe enough to damage the catalytic converter. Stop and diagnose the misfire.

A stored emissions-related fault that is not an immediate threat; retrieve the code and diagnose.

A deep, rhythmic hammering that worsens under load — typically worn rod or main bearings.

A light tapping that rises with RPM — usually a worn lifter or excessive valve lash.

Coolant mixing with oil — typically from a blown head gasket, cracked head/block, or a leaking oil cooler.

Oil burning shows blue smoke and fouled plugs. Past rings = worse under load; past valve seals = puff on startup or deceleration.

Coolant loss with no visible leak points internally: head gasket, cracked head/block, or a leaking intake gasket.

Pressurizes the system with a hand pump to find external coolant leaks and check the cap and head-gasket sealing.

Uses a chemical that changes color if combustion gases are present in the coolant — confirms a head-gasket or cracked-head leak.

Below-atmospheric pressure in the intake manifold; a healthy engine reads a steady ~17–21 in. Hg at idle (varies by engine and altitude).

Combustion in the intake or exhaust outside the cylinder — from incorrect timing, a lean mixture, or a leaking valve.

Unstable idle from a vacuum leak, misfire, low compression, dirty injectors, or a faulty idle-control system.

Set by the manufacturer; #1 is defined per engine layout. Firing order and cylinder ID are needed to diagnose a specific misfire.

The sequence in which the cylinders fire, designed to balance the engine and smooth power delivery.

Too much air or too little fuel. Can cause misfire, hesitation, knock, and higher combustion temperatures.

Too much fuel or too little air. Causes black smoke, fouled plugs, poor economy, and high emissions.

The ratio of cylinder volume at BDC to volume at TDC; higher ratios make more power but need higher-octane fuel.

Diagnose with compression/leak-down, exhaust back-pressure, fuel pressure, and a scan for restrictions or misfires.

Check spark, fuel pressure/volume, compression, and cold-start enrichment; scan for related codes and sensor faults.

Usually a catalytic-converter issue, often from a rich mixture overloading the converter.

Provides rotational inertia and carries the starter ring gear; the flexplate is used with automatic transmissions.

Changes valve opening timing (and sometimes lift) for better power, economy, and emissions across the RPM range.

Uses the scan tool/PCM to measure each cylinder's contribution and flag a weak one without manually shorting plugs.

Driving the truck under the conditions of the complaint to reproduce a noise, miss, or low-power symptom for diagnosis.

The casting that seals the top of the cylinders and houses the valves, seats, guides, and (on OHC engines) the camshaft.

The seal between the cylinder head and block that contains combustion pressure and keeps coolant and oil passages separate.

Causes white smoke, milky oil, overheating, coolant loss, or combustion gases in the coolant.

A non-flat head deck that prevents proper gasket sealing; must be machined flat before reassembly. Check with a straightedge and feeler gauge.

Tightened to a torque value then turned a set angle, stretching into its yield range. TTY bolts are replaced once removed.

A crisscross pattern done in stages so the head clamps evenly without warping. Wrong sequence or over-torque causes gasket failure.

Opens and closes the intake or exhaust port; must seal tightly against its seat to hold compression.

The machined ring the valve face seals against. Worn or recessed seats cause compression loss and poor sealing.

The bore that supports and aligns the valve stem. Wear lets oil into the chamber and the valve seals poorly.

Keeps oil from running down the valve stem into the combustion chamber. Failure causes blue smoke, often a puff on startup.

A valve that no longer seals because heat and leakage eroded its face — causes low compression and a misfire in that cylinder.

The small valve-train gap allowing for thermal expansion. Too little burns valves; too much causes ticking and wear.

Holds the valve slightly open, causing burned valves and lost compression.

Causes a ticking noise and accelerated valve-train wear.

Uses engine oil pressure to maintain zero valve lash automatically, so no periodic adjustment is needed.

A solid valve-train follower that requires periodic manual lash adjustment to spec.

The lobed shaft that opens the valves in time with the crankshaft; its position relative to the crank sets valve timing.

Keeps the camshaft timed to the crankshaft. On an interference engine, a broken belt/chain can bend valves.

An engine in which open valves occupy piston space. A broken timing belt/chain lets pistons strike valves and bend them.

At high RPM a weak valve spring can't close the valve fast enough, so it loses contact with the cam — causing misfire and power loss.

Closes the valve and keeps the follower on the cam. A weak or broken spring causes valve float and poor sealing.

Machining valves and seats to restore a tight seal; includes checking guides, springs, and seals.

Excess clearance lets oil into the chamber and the valve wobble — causing oil consumption and poor sealing.

The main casting that holds the cylinders, crankshaft, and supporting structure of the engine.

The machined cylinder in which the piston travels. Wear creates taper and out-of-round conditions.

The difference in cylinder diameter between the top and bottom of ring travel due to wear. Excess taper calls for reboring.

A cylinder worn unevenly so it is no longer a perfect circle; like taper, a reason to rebore and fit oversize pistons.

The unworn lip at the top of the bore above ring travel. It must be reamed off before removing pistons.

The tool used to cut away the cylinder ridge before pushing pistons out, preventing ring and piston damage.

Machining a worn cylinder to a larger, true diameter so an oversize piston can be fitted.

Finishing the bore with a ~45° crosshatch pattern that helps new rings seat and retain oil.

Converts the pistons' up-and-down motion into rotation. Rides on main bearings in the block.

Links a piston to the crankshaft journal; its big end rides on a rod bearing.

The component that moves in the cylinder, transmitting combustion force through the rod to the crankshaft.

Compression rings seal combustion pressure; the oil-control ring wipes oil from the cylinder wall. Worn rings cause blue smoke and low compression.

The clearance between ring ends in the bore. Too little lets the ends butt and scuff the cylinder when hot; checked with a feeler gauge.

Connects the piston to the small end of the connecting rod, allowing the rod to pivot.

Supports the crankshaft in the block. Excess clearance causes a deep knock and low oil pressure.

Rides between the connecting rod big end and the crank journal. Wear causes a knock that worsens under load.

A calibrated plastic strip crushed between a bearing and journal to measure oil clearance by comparing the flattened width to a chart.

Never rotate the crankshaft while Plastigage is installed — it ruins the reading.

The small gap that holds an oil film between bearing and journal. Too tight starves oil; too loose knocks and drops pressure.

The polished bearing surface on the crank (main or rod). Worn or out-of-round journals require regrinding to undersize.

Finds surface cracks in non-ferrous parts (aluminum heads) using penetrating dye and developer.

Used together to measure bore and journal diameters precisely when checking wear and clearance.

Circulates pressurized oil through the bearings, lifters, and galleries. A worn pump or pickup can cause low oil pressure.

Low oil level, too-thin oil, a worn oil pump, a clogged pickup screen, or worn bearings.

Removes contaminants from circulating oil. Its bypass valve still feeds oil if the filter clogs, protecting the engine.

Oil's resistance to flow. A 5W-30 flows like a 5-weight when cold (the W) and protects like a 30-weight at operating temperature.

Behaves like a thin oil for cold starts and a thicker oil when hot, thanks to viscosity-index improvers.

Limits maximum oil pressure by bleeding off excess, protecting the system from over-pressure on cold starts.

Drilled passages in the block and head that carry pressurized oil to the bearings and valve train.

Transfers heat from the oil to coolant or air; an internal failure can mix oil and coolant.

A temperature-controlled valve that blocks coolant flow to the radiator until the engine warms, then opens to regulate temperature.

Causes the engine to overheat — no coolant flow to the radiator.

Keeps the engine running too cool, hurting fuel economy, emissions, and heater output.

Sheds engine heat to the air as coolant flows through its core; the fan adds airflow at low speeds.

Seals the system and raises the coolant boiling point (about 5–6°F per psi); its vacuum valve lets coolant return from the overflow tank.

The belt-driven pump that circulates coolant through the engine and radiator. A leak often appears at the weep hole.

An ethylene- or propylene-glycol mix with water that resists freezing and boiling and protects against corrosion. Use the specified type.

Pulls air through the radiator at low vehicle speeds. Electric fans run on demand; a fan clutch engages when hot.

A single belt that drives the water pump, alternator, and accessories. A loose or worn belt squeals and can cause overheating.

Maintains proper tension on the serpentine belt automatically; a worn tensioner causes belt noise and slip.

Each psi of system pressure raises coolant's boiling point about 3°C (5–6°F), letting the engine run hotter without boiling.

Carry coolant between engine and radiator; cracked, swollen, or soft hoses can burst and cause overheating.

Steps up battery voltage to the tens of thousands of volts needed to jump the spark-plug gap.

Delivers the spark that ignites the mixture. Reading plug condition (fouled, oily, white) helps diagnose combustion problems.

The set distance the spark jumps; too wide or too narrow a gap causes weak spark and misfires.

A plug coated with carbon (rich), oil (worn rings/seals), or fuel (flooding) that misfires; reading the plug guides diagnosis.

Uses individual coils (often one per plug) controlled by the PCM instead of a distributor.

Replaces the distributor with PCM-controlled coils, improving timing accuracy and removing distributor wear points.

Routes high voltage to each spark plug in firing order and controls spark timing on older ignition systems.

When the spark fires relative to piston position. Too advanced causes knock; too retarded loses power and runs hot.

Detects detonation so the PCM can retard ignition timing to protect the engine.

Reports crankshaft speed and position; the primary input for ignition timing and engine RPM.

Reports camshaft (valve) timing to the PCM for ignition and injection control and cylinder identification.

Controls coil firing (when not handled directly by the PCM) for proper spark timing.

How fast a plug dissipates heat; too hot causes pre-ignition, too cold causes fouling. Use the specified plug.

The high-voltage side (coil to plug). Tested with an oscilloscope or a spark tester to find weak spark or open circuits.

The low-voltage side controlling the coil (battery, switch, module/PCM); a fault here can cause a complete no-spark condition.

Detonation heard under acceleration; suspect low octane, over-advanced timing, lean mixture, or carbon buildup.

A fuel's resistance to knock. Higher octane resists detonation; using too low an octane can cause spark knock.

A grouped set of ignition coils; one coil can fire two plugs (waste spark) or each cylinder may have its own coil.

One coil fires two plugs at once — one on compression (useful) and one on exhaust (wasted) — a common distributorless design.

A tool placed in the plug circuit to confirm the coil is producing a strong spark during cranking.

Check primary power and ground, crank/cam sensor signals, the module/PCM, and the coil before condemning a part.

Spark jumping between adjacent plug wires or terminals, causing a misfire; keep wires routed and gapped per spec.

Reference marks on the crank pulley/balancer used to verify base timing with a timing light on applicable engines.

A deposit or hot plug ignites the mixture before the spark (pre-ignition); causes knock and possible piston damage.

The proportion of air to fuel by weight; the ideal (stoichiometric) ratio for gasoline is about 14.7:1.

The ideal 14.7:1 air-fuel ratio for complete combustion of gasoline; the PCM trims fueling toward it.

An electrically controlled valve that sprays a metered amount of fuel into the intake or cylinder. Clogged or leaking injectors upset the mixture.

Maintains correct fuel-rail pressure so injectors deliver the right amount of fuel.

Delivers fuel from the tank to the injectors at the required pressure and volume. A weak pump leans the mixture under load.

Removes dirt and rust from fuel before the injectors; a clogged filter starves the engine, especially under load.

Injects fuel into the intake port just ahead of the intake valve; the common gasoline-engine fuel delivery method.

The manifold that feeds pressurized fuel to all the injectors; pressure here is checked during a fuel-system diagnosis.

Cleans incoming air. A clogged filter restricts airflow, richening the mixture and reducing power.

Controls airflow into the intake based on accelerator input; carbon buildup can cause rough idle.

Distributes the air (or air-fuel mixture) to the cylinders. A leaking gasket causes a lean condition and rough idle.

Unmetered air entering after the MAF leans the mixture, causing high idle, rough idle, and lean codes.

The ducting from the air filter to the throttle body; cracks or loose clamps after the MAF draw in unmetered air and lean the mixture.

Compares each injector's contribution (pressure drop or power) to find a clogged or weak injector causing a misfire.

Collects exhaust from the cylinders into the exhaust system; cracks or leaks cause ticking noise and false O₂ readings.

Reduces exhaust noise. A rusted or internally collapsed muffler can restrict flow.

Resistance to exhaust flow; high back-pressure (plugged converter/muffler) reduces power and can overheat the engine.

Chokes the exhaust, causing power loss especially at higher RPM and high back-pressure.

A misfire from too little fuel — often a vacuum leak, weak fuel supply, or dirty injectors.

A misfire from too much fuel fouling the plug — leaking injector, high fuel pressure, or a faulty sensor.

Connects a gauge to the fuel rail to check pressure against spec; low pressure leans the mixture and causes hard starts.

Measures how much fuel the pump delivers over time; a pump can hold pressure yet fail to deliver enough volume under load.

The final section of the exhaust that releases treated gases; a crushed or restricted tailpipe raises back-pressure and cuts power.

Lets outside air reach the sensor, making the mixture read falsely lean and causing the PCM to over-fuel.

Converts CO, hydrocarbons, and NOx into less harmful CO₂, water, nitrogen, and oxygen. Needs the correct air-fuel ratio to work.

The post-converter oxygen sensor monitors catalyst efficiency by comparing its signal to the upstream sensor.

Running too rich for long periods overheats and destroys the converter; an internal restriction also causes overheating.

Exhaust Gas Recirculation — admits inert exhaust into the intake to lower combustion temperature and reduce NOx.

Causes rough idle and stalling because exhaust gas dilutes the mixture at idle.

Raises NOx and can cause spark knock (detonation) under load.

Positive Crankcase Ventilation — draws blow-by from the crankcase back into the intake to be burned, cutting emissions.

Acts like a vacuum leak, leaning and roughening the idle.

Builds crankcase pressure that pushes oil out through seals and gaskets.

Captures fuel-tank vapors and routes them to be burned; a loose gas cap can set an EVAP leak code.

Stores fuel-tank vapors in the EVAP system until the purge valve sends them to the engine to be burned.

Lets stored vapors flow from the canister into the intake under PCM control; stuck open it can cause a rough idle.

Emissions formed at high combustion temperature; EGR reduces them by lowering peak cylinder temperature.

A product of incomplete combustion (rich mixture); the catalytic converter oxidizes it to carbon dioxide.

Unburned fuel in the exhaust from misfire or a rich mixture; the converter oxidizes them to CO₂ and water.

Adds fresh air to the exhaust to help the converter oxidize CO and HC, especially during warm-up.

Seals the fuel system; a loose or faulty cap is a common cause of a small EVAP leak code (P0455/P0456-type).

Sets when the downstream O₂ signal mirrors the upstream too closely, indicating a converter no longer cleaning the exhaust.

Removing or disabling emissions devices is illegal and causes failed inspections, higher emissions, and drivability faults.

Measures tailpipe gases (HC, CO, NOx) or reads OBD-II monitors to confirm emissions controls are functioning.

Measures oxygen in the exhaust and tells the PCM if the mixture is rich or lean for closed-loop fuel control.

Reads the exact air-fuel ratio across a range, not just rich/lean, for more precise fuel control.

A device that reads DTCs, live data, and freeze-frame from the OBD-II system to guide diagnosis.

Tells the PCM how far the throttle is open so it can adjust fuel and timing; a glitchy TPS causes hesitation or surging.

Reports coolant temperature to the PCM, affecting fuel mixture, timing, fan control, and the temperature gauge.

Reports incoming air temperature so the PCM can fine-tune fuel and timing for changes in air density.

Measures intake manifold pressure (engine load) so the PCM can calculate fuel and timing.

Measures the amount of air entering the engine so the PCM can match fuel delivery.

The PCM's immediate correction to injector pulse based on the O₂ sensor; swings quickly to hold the mixture at 14.7:1.

Sensors send the PCM a varying voltage (e.g., TPS, MAP), a frequency (some MAF), or a switching signal; the right test depends on the type.

A learned, slower correction the PCM stores over time; a large LTFT (±10% or more) signals a persistent lean or rich fault.

Large positive fuel trim = the engine is running lean (vacuum leak/weak fuel); large negative trim = running rich (leaking injector/high pressure).

PCM-controlled outputs — injectors, ignition coils, idle-air control, EGR, and the EVAP purge — that act on its commands.

Primary PCM inputs for ignition timing, injection, RPM, and cylinder identification; a fault can cause a no-start or misfire.

A PCM-controlled actuator that meters air around a closed throttle to set idle speed; a faulty IAC causes high, low, or unstable idle.

The PCM supplies a steady 5-volt reference to many sensors; a shorted reference can disable several sensors at once.

Real-time sensor and actuator values the scan tool reads from the PCM, used to compare actual readings against expected ones.

Self-tests the PCM runs (catalyst, O₂, EVAP, EGR, misfire) that must be 'ready' to pass an emissions inspection.

A specific sequence of driving conditions that lets the PCM run its OBD-II monitors and set readiness after codes are cleared.

The 'check engine' light the PCM turns on for an emissions-related fault; flashing means an active converter-damaging misfire.

The computer that uses sensor inputs to control fuel, spark, and emissions for the engine.

On-Board Diagnostics II — the standardized system that monitors emissions components and stores diagnostic trouble codes (DTCs).

A code stored by the PCM identifying a detected fault (e.g., P0300 = random misfire).

A snapshot of sensor readings captured when a trouble code set, used to recreate the conditions of a fault.

The PCM uses O₂ sensor feedback to continuously trim fuel toward the ideal ratio once the engine is warm.

On a cold start the PCM ignores the O₂ sensor and uses programmed values until the engine and sensor warm up.