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The Compact Diesel exam has 60 questions and runs 1 hour.
These 10 free Compact Diesel questions are organized by exam domain, so you can see how each part of the Compact Diesel Technician Certification blueprint is tested. Reveal the answer and explanation under each question.
During a leak check on a common-rail compact diesel, a fine jet of fuel strikes a technician's hand. The puncture is tiny and causes little pain. Once the machine is safely shut down, the technician should:
Correct answer: B - Obtain urgent medical assessment for possible fluid injection.
An engine-bracket tightening procedure calls for clean, dry bolt threads. A replacement bolt arrives coated with oil. Which preparation keeps the stated torque specification valid?
Correct answer: A - Clean the bolt and restore the specified dry-thread condition.
A bore-inspection note records equal cylinder diameters at two depths. Both measurements were made with a two-point gauge aligned in the same direction. Which conclusion can be entered from these readings alone?
Correct answer: A - No taper was detected along the measured direction.
A compact diesel runs roughly immediately after its fuel filter is replaced. The filter is upstream of the lift pump. An approved diagnostic line just downstream of the filter shows bubbles during operation, yet the housing and its connections remain dry outside. Which fault best accounts for that combination?
Correct answer: C - An incorrectly seated seal admitting air on the suction side
A three-cylinder common-rail compact diesel cranks normally but cannot build the required rail pressure. Supply pressure and flow pass their checks. During the specified 30-second cranking test, injector return volumes are 2 mL, 3 mL and 20 mL for cylinders 1, 2 and 3. The permitted maximum is 5 mL per injector. Which fault is best supported by these tests?
Correct answer: D - Injector 3 is losing excessive fuel through its internal return.
A slow-cranking diesel has a battery that passes its load test and measures 12.7 V at rest. During cranking, voltage across the battery posts is 10.9 V. The complete positive path, including solenoid contacts, loses 0.85 V; the motor-case-to-negative-post return loses 0.15 V. This engine requires at least 10.3 V at the motor, with maximum positive and return losses of 0.30 V and 0.20 V. Which assessment fits the measurements?
Correct answer: C - The motor receives 9.9 V; locate excessive resistance in the positive path.
"The air filter looks dusty; replacing it now would be cheap insurance." Before approving that work, the foreman checks the engine's service criteria: restriction is 4 kPa at the required full-load condition, replacement is due at 6 kPa, the calendar limit is not due, and filter integrity is satisfactory. What should the foreman authorize?
Correct answer: B - Keep the filter in service and monitor restriction as specified.
In a conventional four-stroke compact diesel, the camshaft must operate the valves once per complete engine cycle. Its rotational speed is:
Correct answer: D - One-half of the crankshaft's rotational speed.
A coolant sample passes the engine's freeze-protection requirement when tested with a calibrated refractometer on the correct glycol scale. The existing coolant's inhibitor formulation is unknown, and a proposed top-up product has the same color. What has the test actually established?
Correct answer: D - Freeze protection is satisfactory; coolant compatibility remains unverified.
When other fuel properties and test conditions are comparable, a higher diesel cetane number primarily indicates:
Correct answer: B - A shorter delay between fuel injection and ignition
The Compact Diesel exam also covers these domains. Drill them in the full free practice test:
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