ASE T1 practice test: gasoline truck engines

Correct: Stripped spark plug threads in an aluminum head are routinely repaired with a thread insert, while Technician B's caustic tank would attack the aluminum.

Incorrect: Hot caustic (lye) solution eats aluminum, so this head needs a cleaner made for aluminum; Technician B is wrong.

Incorrect: Only Technician A holds up; a caustic tank corrodes aluminum, so Technician B's cleaning method would damage the head.

Incorrect: Technician A is right: a thread insert is a standard repair for damaged plug threads in an aluminum head.

Correct: A cracked fuel cap seal is a classic small EVAP leak, so the cap is checked first before the system is smoke tested.

Incorrect: A purge solenoid with an open coil cannot be commanded open; that sets a purge circuit or flow code, not a small leak.

Incorrect: A plugged canister vent filter blocks airflow and sets a vent restriction code; it adds no leak path.

Incorrect: An injector O-ring seals liquid fuel at the intake, outside the sealed vapor system that the EVAP monitor tests.

Incorrect: A signal wire shorted to ground pulls the reading toward 0 V and sets a circuit low code.

Incorrect: An open 5 V reference leaves the sensor unpowered, so the signal drops toward 0 V, the opposite of 4.9 V.

Correct: With an open sensor ground, the signal line floats up toward the 5 V reference, which matches the 4.9 V reading and the circuit high code.

Incorrect: A large vacuum leak raises manifold pressure, but not to 4.9 V at idle, and it does not set a circuit high code.

Incorrect: An open in the signal circuit would still read −40 °F with the jumper installed at the connector, because the jumper would not bridge the break.

Correct: Jumping the harness terminals made the reading jump to full hot, which proves the wiring and module work, so the ECT sensor itself is open.

Incorrect: The module answered the jumper with a full-hot reading, which shows its temperature input is working.

Incorrect: A short to ground in the signal wire makes the scan tool read very hot, not −40 °F.

Correct: A damaged cam reluctor wheel gives the module a poor cam signal, so it takes extra cranking to sync and sets a CMP code.

Incorrect: A weak coil on one cylinder causes a misfire on that cylinder; it does not cause a long crank or a cam sensor code.

Incorrect: A leaking fuel pump check valve can make the engine crank longer, but it does not explain a camshaft position code.

Incorrect: With no crank sensor signal, most engines will not start at all, and the stored code would be for the crank sensor.

Incorrect: Too hot a plug heat range causes preignition or knock, not a total loss of spark.

Incorrect: A vacuum leak at the PCV hose gives a lean, rough idle; it does not kill the spark.

Incorrect: A leaking check valve makes a hot restart crank longer, but spark would still be present at the plugs.

Correct: Losing spark on every cylinder only when hot, with a restart once it cools, points to a shared ignition part that fails with heat, such as the ignition control module.

Correct: Each cam bearing must have its oil hole lined up with the block's oil passage; a misaligned hole starves that journal and the valve train beyond it.

Incorrect: Cam bearings are pressed in dry or lightly lubricated on the back for a tight fit; sealer on the outside is not used.

Incorrect: Cam journals are not ground to fit new bearings; standard bearings fit standard journals.

Incorrect: No rule says the seams face the crankshaft; what matters is that the oil holes line up.

Correct: Two distinct layers mean water, or ethanol that has absorbed water and phase-separated, has collected in the fuel.

Incorrect: Low octane causes spark knock under load, but octane cannot be seen in a sample and does not make layers.

Incorrect: Diesel mixes into gasoline without forming a separate layer, so it is not what a two-layer sample shows.

Incorrect: Fuel additives stay dissolved in the gasoline and do not settle into their own layer.

Incorrect: An EGR valve stuck closed raises combustion temperature and causes spark knock, but it does not feed unburned fuel into the converter to overheat it.

Correct: Unburned fuel from a misfiring cylinder burns inside the converter and can overheat the substrate until it melts; a stuck-closed EGR valve does not do that.

Incorrect: Only Technician B is right: an EGR valve stuck closed causes spark knock and high NOx, not a melted converter.

Incorrect: Technician B is right: fuel from a misfiring cylinder burns in the converter and can melt it.

Incorrect: Forcing a large probe into a female terminal spreads it and creates a new intermittent, so Technician A is wrong, and so is Technician B.

Incorrect: RTV silicone gives off acid as it cures and corrodes the terminals; cleaned terminals are protected with dielectric grease or a proper seal, so Technician B is wrong.

Incorrect: Both methods do harm: a large probe spreads the terminal, and RTV corrodes it while curing.

Correct: A big probe spreads a female terminal and RTV releases acid as it cures, so neither statement is acceptable; back-probe or use the correct test lead and protect terminals with dielectric grease.