ASE A9 Light Vehicle Diesel Engines flashcards

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

Cranking compression spec

Minimum cylinder pressure during cranking, typically 300-450 psi on light-duty diesels; a cylinder far below the highest cylinder indicates ring, valve, or head gasket leakage.

Wet compression test

Adding oil to a cylinder and re-testing compression; a pressure rise points to ring or cylinder wall sealing, while little change points to valve or head gasket leakage.

Cylinder contribution test

Disabling each injector in turn while monitoring RPM or exhaust temperature change; the cylinder producing the least change is the weak or misfiring one.

Blowby diagnosis

Crankcase pressure from combustion gases escaping past rings or pistons; measured at the oil fill or dipstick tube and compared to specification to assess internal wear.

White smoke causes

Unburned fuel vapor from cold cylinders, glow plug faults, low compression, retarded injection timing, or coolant ingress; smoke that clears when warm suggests cold-start fuel or glow issues.

Cylinder head flatness

Checked with a straightedge and feeler gauge; allowable warpage on many light-duty diesel heads is about 0.002-0.004 in, and resurfacing alters valve recession and clearance.

Valve recession limit

The amount a valve has sunk into its seat, measured as stem height; exceeding the wear limit requires seat replacement because lash adjustment cannot restore it.

Torque-to-yield bolts

Head and main fasteners stretched into their elastic range during tightening; they must be replaced and torqued in the specified sequence and stages to achieve correct clamp load.

Piston protrusion

Height of the piston crown above the block deck at TDC; it sets compression ratio and must be within spec to prevent piston-to-valve contact.

Camshaft timing verification

Confirming cam and crank synchronization with timing pins or marks; diesel valve-to-piston clearance is small, so incorrect timing can cause severe internal damage.

Diesel oil service category

API category such as CJ-4 or CK-4 specifying the oil's formulation; using the wrong category can damage aftertreatment catalysts or the DPF.

Oil pressure verification

Confirming dash gauge readings with a mechanical gauge at the sender port; low hot-idle pressure can come from diluted oil, worn bearings, or a restricted pickup.

Filter bypass valve

A valve that opens when differential pressure across the oil filter is high, allowing unfiltered oil to flow so the engine is not starved of lubrication.

Coolant chemistry match

Using the specified OAT or HOAT coolant; mixing incompatible chemistries can gel and plug the radiator, heater core, and EGR cooler.

Combustion gas in coolant

A failed head gasket or cracked casting allows combustion gas into the cooling system; detected with a chemical block tester or by bubbles in the radiator.

EGR cooler leak

An internal coolant leak in the EGR cooler causes coolant loss, white exhaust, and pressure in the cooling system; a common coolant-loss point on modern diesels.

Turbo boost control

Boost is regulated by a wastegate on fixed-geometry turbos or by variable vanes on VNT/VGT turbos; a stuck actuator causes underboost or overboost codes.

Charge-air leak symptom

A leak in the intercooler or intake boots causes low boost, black smoke, and power loss; pressure-test the intake tract and look for oil mist at joints.

Turbo shaft play check

Measuring axial and radial movement of the turbo shaft; excessive radial play or wheel-to-housing contact requires turbo replacement, often caused by oil starvation or coking.

Exhaust backpressure

Pressure measured upstream of the DPF or turbo; excessive backpressure from a plugged filter or collapsed pipe reduces power and raises exhaust temperatures.

Air filter restriction

Measured with a water manometer or restriction gauge; exceeding the specified restriction (often around 25 in H2O) requires filter replacement.

Common-rail pressure control

The ECM commands rail pressure through a pressure control valve or pump metering unit; low cranking rail pressure can come from excessive injector return flow or a weak pump.

Injector leak-off test

Measuring return flow from each injector; excessive return flow from one injector can prevent the rail from building enough pressure to start the engine.

Injector classification coding

Programming the injector's trim code into the ECM after replacement so the ECM applies the correct delivery correction for that specific injector.

Retarded injection timing

Injection occurring later than specified; it causes white smoke, hard starting, and higher exhaust temperatures, while advanced timing raises NOx and can cause rough running.

Piezo injector testing

Piezo injectors are driven by high voltage and cannot be checked with a standard ohmmeter like solenoid injectors; use the manufacturer's diagnostic procedure instead.

Cranking speed requirement

Diesel engines need adequate cranking RPM, typically 150-250, to build compression heat; a weak battery, bad cable, or failing starter causes hard or no starting.

Voltage drop testing

Loading a circuit and measuring voltage lost across cables and connections; generally no more than about 0.5 V per cable or connection is acceptable.

Glow plug afterglow

Glow plugs remain powered briefly after startup under module control to reduce white smoke and misfire while the engine warms; a failed plug causes cold-start symptoms.

CAN bus termination

The network has terminating resistors that produce about 60 ohms across CAN high and low; incorrect resistance or voltage indicates a wiring or module communication fault.

DPF regeneration

Burning accumulated soot at high exhaust temperature; passive regeneration occurs during high-load driving, while active regeneration is ECM-initiated with post-injection or exhaust dosing.

SCR and DEF operation

SCR injects DEF, a 32.5% urea solution, into the exhaust to reduce NOx; low DEF level, poor quality, or a failed doser causes derate and NOx efficiency codes.