ASE T1 Gasoline Engines (Medium/Heavy Truck) flashcards

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

Cylinder leakage test

Introduces compressed air into a cylinder at TDC and measures the percentage leaking; air escaping at the intake, exhaust, or crankcase locates the faulty component.

Vacuum gauge diagnosis

A steady 17-22 in-Hg at idle indicates a healthy engine; a fluctuating or dropping needle reveals a vacuum leak, worn rings, or a restricted exhaust.

Wet compression test

Adding oil to a low cylinder raises compression if the rings are worn; if compression stays low, the valves or head gasket are at fault.

Blow-by test

Steady crankcase vapor flow indicates general ring wear; a rhythmic puffing flow indicates one damaged cylinder or piston.

Valve lash adjustment

Sets the clearance between the rocker and valve stem; too tight holds valves open and burns them, too loose causes noise and reduced lift.

Valve recession

Occurs when valves sink into their seats over time, reducing installed spring height and changing lash; measured by valve stem height.

Camshaft lobe lift

Measured as the difference between the lobe's base circle and its peak; worn lobes reduce lift and cause misfires unrelated to ignition.

Valve guide clearance

The gap between the valve stem and guide; excessive clearance lets oil into the combustion chamber and causes valve seal failure.

Head warpage check

A straightedge and feeler gauge along the length, width, and diagonals of the head reveal warpage; compare against the manufacturer's flatness limit.

Plastigage

A crushable plastic strip placed on a journal; its crushed width indicates bearing clearance when compared to the printed scale.

Crankshaft end play

Axial movement of the crankshaft measured with a dial indicator; excessive play indicates a worn thrust bearing or worn thrust surface.

Bearing fatigue failure

Cracking and flaking of the bearing lining caused by overload, detonation, or excessive clearance; the bearing surface shows a cracked, flaked pattern.

Piston ring end gap

The gap between ring ends when squared in the bore; too small causes ring butting and breakage, too large causes blow-by and oil consumption.

Torque-to-yield bolts

Bolts tightened to a torque and then an additional angle; they stretch permanently and must be replaced when reused beyond specification.

Cylinder bore taper

The difference in bore diameter from top to bottom; excessive taper causes ring sealing loss and requires boring or honing.

Oil pressure test

A mechanical gauge at the specified rpm and temperature confirms pressure; low pressure at speed indicates worn bearings or a weak pump.

Oil filter bypass valve

Opens when the filter is clogged to maintain oil flow; it allows unfiltered oil to circulate and signals a filter that must be changed.

PCV system

Positive crankcase ventilation routes blow-by gases into the intake; a clogged PCV valve causes oil consumption and seal leakage.

Oil analysis

Lab testing of oil for wear metals and coolant; elevated iron indicates cylinder wear, elevated copper or lead indicates bearing wear.

Combustion gas test

A chemical block tester samples coolant vapors; a color change confirms combustion gases, indicating a head gasket or cracked head.

Thermostat test

Heating the thermostat in water and measuring its opening temperature confirms function; a stuck-open unit causes slow warm-up and low heater output.

Radiator cap pressure test

Testing the cap to its rated pressure confirms it holds; a weak cap lowers the coolant boiling point and allows coolant loss.

Fan clutch test

A viscous fan clutch should engage when hot; a failed clutch causes overheating at idle and low speed.

Turbocharger shaft play

Checking axial and radial play reveals bearing wear; excessive play allows the wheel to contact the housing and damages the turbo.

Exhaust backpressure test

A gauge at the exhaust measures restriction; high backpressure from a plugged catalyst or muffler reduces power and can cause overheating.

EGR valve stuck open

Allows exhaust gas into the intake at idle, causing rough running, stalling, and black smoke; the valve must be cleaned or replaced.

Injector balance test

Each injector is fired and the resulting pressure drop or rpm change is compared; a weak injector shows a smaller drop than the others.

Fuel volume test

Measures fuel delivered over a set time; adequate pressure with low volume indicates a restricted filter or a failing pump.

Common rail pressure

Low rail pressure during cranking prevents starting; check the pressure sensor, regulator, and high-pressure pump for faults.

Spark plug reading

Plug color and deposits reveal mixture and oil conditions; black soot indicates rich mixture, oily deposits indicate worn rings or guides.

CKP sensor

The crankshaft position sensor provides engine speed and position to the ECM; a failed sensor prevents both spark and fuel delivery.

Voltage drop test

Measures voltage lost across a cable or connection while current flows; a drop above 0.5V indicates excessive resistance.