ASE T2 Diesel Engines (Medium/Heavy Truck) flashcards

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

Valve lash measurement point

Lash is measured between the rocker arm and valve stem tip (or at the pushrod) with the lifter on the cam base circle and the cylinder at TDC compression.

Valve recession limit

The maximum allowable valve tip height above the head deck; typically about 0.060 in intake and 0.030 in exhaust before seat replacement is required.

Head gasket leak test

Combustion gas in the cooling system is confirmed with a chemical block tester that changes color, or by bubbles in the radiator during cranking.

Torque-to-yield head bolts

Fasteners stretched into the yield range during tightening; they must be measured for length or diameter and replaced if beyond specification.

Cylinder taper limit

The maximum allowable difference between top and bottom bore diameter, typically 0.002-0.004 in; exceeding it requires boring or sleeving.

Liner protrusion

The height of a wet cylinder liner above the block deck, usually 0.002-0.005 in, which ensures head gasket sealing and clamping.

Crankshaft end play

Axial movement of the crankshaft measured with a dial indicator, typically 0.004-0.012 in; excessive play indicates worn thrust washers.

Block deck flatness

The allowable deviation of the block deck from flat, usually 0.002-0.004 in in a 6 in span and 0.008 in overall.

Oil pressure specification

Typical heavy-duty diesel oil pressure is 30-60 psi at rated rpm and at least 10-15 psi at idle when the engine is warm.

Cooling system pressure test

The system is pressurized to 1.5 times the cap rating, not higher, to locate external leaks without damaging the radiator or hoses.

Combustion gas in coolant

Detected with a chemical block tester or by observing bubbles in the radiator with the cap off, indicating a failed head gasket or cracked head.

Oil filter bypass valve

A spring-loaded valve that opens at roughly 15-20 psi differential to keep oil flowing if the filter becomes restricted.

Intake restriction limit

Maximum allowable vacuum in the intake, about 25 in H2O with a clean filter and 30 in H2O when the restriction indicator trips.

Exhaust backpressure limit

Maximum allowable exhaust pressure at rated speed, typically 3 in Hg (about 40 in H2O); higher values indicate a restricted exhaust or DPF.

Turbo shaft play limits

End play of about 0.002-0.004 in and radial play of about 0.004-0.008 in; excessive play indicates worn bearings and requires replacement.

Charge-air cooler leak test

The cooler is pressurized to about 30 psi and checked with soap solution; leaks cause low boost, black smoke, and low power.

DPF differential pressure

The pressure drop across the filter; a high delta-P at low exhaust flow indicates soot or ash loading and requires regeneration or cleaning.

Common-rail injection pressure

Pressure in the high-pressure rail can exceed 30,000 psi; high-pressure lines must never be cracked open to bleed air.

Low-pressure fuel supply

The lift pump supply to the injection pump is typically 5-15 psi; low supply causes hard starting, low power, and injector damage.

Injector return flow test

Measuring fuel returned from each injector; excessive return indicates a worn injector that causes rough running and hard starting.

Injection timing effects

Advanced timing causes knock and high NOx; retarded timing causes white smoke, poor power, and high exhaust temperature.

Battery state of charge

A 12V battery at rest reads 12.6V when fully charged, 12.4V at about 75%, and 12.0V at about 25% state of charge.

Alternator charging voltage

With the engine running and loads off, charging voltage at the battery should be about 13.8-14.4V for a healthy alternator.

Cranking voltage test

Battery voltage during cranking should stay above 9.6V; lower readings indicate a weak battery or excessive cable resistance.

Parasitic draw limit

After modules sleep, current draw should be below about 50 mA; higher draw discharges the battery and indicates a fault.

5V reference diagnosis

A sensor circuit reading 0V indicates a short to ground, while reading 5V with the sensor disconnected indicates an open circuit.

J1939 bus resistance

With power off, resistance across CAN high and CAN low should be about 60 ohms, reflecting two 120-ohm terminating resistors in parallel.

Cam and crank sync

The ECM compares cam and crank signals; loss of cam sync causes long crank times and a synchronization fault code.

ECM ground verification

ECM power and ground must be checked at the connector under load; a poor ground causes multiple unrelated fault codes.

Slave piston clearance

The clearance between the Jake brake slave piston and valve crosshead, typically 0.015-0.025 in; incorrect clearance causes weak braking.

Jake brake oil pressure

Compression-release brakes require oil supply of about 15-30 psi at operating temperature; low pressure causes weak or no braking.

Exhaust brake butterfly

A valve that restricts exhaust flow to create backpressure; it must fully open when off or it causes power loss and high backpressure.

Retarder low-rpm cutoff

The brake disengages below about 800-1000 rpm to prevent engine stall; this cutoff is normal operation, not a fault.