Five free practice questions on diesel fuel systems and engine controls: content area F of the ASE T2 Diesel Engines test, 16 of its 55 scored questions (29.1%). They are in the ASE format: four options, one best answer. Answer each one before opening the explanation. No account, no email.
01The questions
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Why does the pickup (draw) tube in a diesel fuel tank end a short distance above the bottom of the tank instead of touching it?
- To keep the tube from drawing air during braking
- To keep warm return fuel from being drawn back in
- To leave a reserve after the gauge reads empty
- To leave settled water and sediment behind
Show the answer
D. Correct. Water is heavier than diesel fuel and settles to the bottom of the tank with dirt and rust, so ending the pickup tube above the bottom leaves that layer behind instead of feeding it to the filters. The water and sediment are drained from the tank's drain or sump at service so the layer never reaches the pickup.
Why not the others
A. Raising the pickup tube would make it easier, not harder, to uncover when fuel sloshes forward under braking. Its end sits above the bottom so it does not draw in the settled water and sediment there.
B. Return fuel is kept away from the pickup by where the return tube enters the tank, not by the pickup's height. Ending the pickup above the bottom keeps it out of the water and sediment that settle there.
C. The point at which the gauge reads empty is set by the level sender, not by the pickup tube. The gap under the pickup is there so the tube does not draw the water and sediment that collect on the tank bottom.
ID T2-F-006 · Task T2-F-1 (ASE task list)
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During an inspection of the high-pressure injection lines on a truck engine, any of these findings calls for replacing the line EXCEPT:
- a line worn shiny and thin where it rubbed a bracket.
- a line with a kink or a flattened bend.
- a missing rubber isolator in one line clamp.
- a line whose cone end is cracked or out of shape.
Show the answer
C. Correct. A missing isolator lets the line vibrate against its clamp, so the isolator or clamp is replaced right away, and the line stays in service if it shows no wear where it touched the clamp. The line itself is replaced when it is worn, kinked, cracked or its sealing cone is damaged.
Why not the others
A. This calls for a new line. Wear thins the wall of a line that carries injection pressure, and a high-pressure line is replaced, not patched or brazed; the cause of the rubbing is corrected too.
B. This calls for a new line. A kink or flattened bend narrows the bore and leaves a weak point that can crack under the pressure pulses of every injection.
D. This calls for a new line. The cone end is the sealing surface; cracked or deformed, it cannot seal against its seat however the nut is tightened.
ID T2-F-014 · Task T2-F-5 (ASE task list)
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With the engine running, fuel is seeping from the nut at the injector end of a high-pressure line. Technician A says coating the nut's threads with thread sealant will stop the leak. Technician B says tightening that nut well past its torque specification is the right way to stop the leak. Who is right?
- A only
- B only
- Both A and B
- Neither A nor B
Show the answer
D. Correct. Technician A is wrong: a high-pressure fitting seals metal to metal where the line's cone meets its seat, and the threads only supply clamping force, so sealant cannot stop the leak and pieces of it can reach the injector. Technician B is wrong: tightening past the torque specification deforms the cone and seat and can crack the line; with the engine shut down, the cone and seat are inspected, the nut is torqued to specification and a damaged line is replaced.
Why not the others
A. Technician A is wrong: the fitting seals where the line's cone meets its seat, and the threads only clamp, so sealant on them cannot stop the leak. Technician B is wrong too: overtightening crushes the cone seat, so the nut goes only to its torque specification and a damaged line is replaced.
B. Technician B is wrong: going past the torque specification crushes the cone seat and can crack the line, so a fitting that leaks at specified torque has a damaged seat or line. Technician A is wrong as well, since the threads are not the sealing surface.
C. Neither technician is right. Technician A would put sealant on threads that do not seal and risk pieces of it reaching the injector; Technician B would deform the cone seat by tightening past the torque specification.
ID T2-F-020 · Task T2-F-5 (ASE task list)
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On an EUI engine that feeds its injectors through a fuel passage drilled in the cylinder head, the manufacturer's procedure calls for draining the fuel from that passage before any injector is removed. What is the reason?
- So fuel cannot run down the open bores onto the pistons
- To bleed off injection pressure held in the head passage
- So no air is trapped in the passage when it is refilled
- To flush out dirt loosened as the injectors come out
Show the answer
A. Correct. With an injector out, its bore opens the head's fuel passage to the combustion chamber, so fuel left in the passage runs down onto the piston. Liquid does not compress, so a cylinder holding fuel can hydraulically lock the engine when it is cranked; draining the passage first keeps the fuel out, and the system is primed once the injectors are back in.
Why not the others
B. The head passage holds only low supply pressure from the transfer pump, and none once the engine is stopped; injection pressure exists only inside each injector while its plunger is driven with the control valve closed. The fuel is drained so it cannot run down the open bores into the cylinders.
C. Draining lets air into the passage rather than keeping it out, which is why the system is primed after the injectors are reinstalled. The reason for draining is to keep the fuel from running down the open bores into the cylinders.
D. The passage is drained before the injectors are disturbed, so the draining cannot carry away dirt they loosen; that dirt is kept out by cleaning around each injector first and plugging the open bore. The fuel is drained so it cannot run down the bores into the cylinders.
ID T2-F-029 · Task T2-F-8 (ASE task list)
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A truck's engine protection system acts on a low coolant level signal only after the signal has been present without a break for the time the manufacturer specifies. What is the reason for this delay?
- So coolant expansion has time to refill the surge tank
- So sloshing on grades and in stops cannot trip it
- So the sensor's probe can warm up before it reads
- So the driver has time to add coolant on the road
Show the answer
B. Correct. Coolant moves in the tank on grades, in turns and in hard stops, and can uncover the level probe briefly even when the level is correct. Requiring the signal to last for the specified time keeps those moments from causing a false derate or shutdown.
Why not the others
A. Expansion raises the level as the engine warms, but the delay is not there to wait for warm-up. It filters out short dips in the signal, such as coolant sloshing away from the probe on grades and in hard stops.
C. A warm-up allowance would be needed only once after start-up, not every time the signal appears, and the probe senses the coolant around it directly. The delay exists to ignore short dips in the signal, such as sloshing on grades and in hard stops.
D. The protection system does not wait for the driver to service the truck; a real low level remains present and is acted on once the delay passes. The delay filters out short dips such as sloshing.
ID T2-F-039 · Task T2-F-10 (ASE task list)
02Answer key
| Question | Answer |
|---|---|
| Q1 | D |
| Q2 | C |
| Q3 | D |
| Q4 | A |
| Q5 | B |
03What area F covers
This content area covers the diesel fuel system from tank to injector and the electronics that run it: tanks, lines and transfer pumps, filters, water separators and heaters, priming and bleeding, low-pressure regulation, high-pressure lines, common rail, HEUI and EUI systems, pedal and speed controls, engine protection, connectors and wiring, scan tool calibrations and parameters, and meter and scope readings.
The ASE test specification calls this content area “Fuel System Diagnosis and Repair”. It carries 16 of the 55 scored questions, 29.1% of the test.
- Inspect tanks, lines, transfer pumps and filters
- Find air, water and contamination; prime and bleed
- Test low-pressure regulators and restrictive fittings
- Inspect high-pressure lines and their fittings
- Test common rail, HEUI and EUI systems on the engine
- Diagnose pedal, speed control and engine protection circuits
- Update calibrations, injector codes and programmable parameters
- Read voltage, resistance and current with a DMM or scope
04What the questions turn on
Where the bubbles appear
A clear tube shows where air gets in. Bubbles at the tank outlet only below half a tank point to a cracked pickup tube. Solid fuel at the secondary filter but bubbles in the return point to cylinder gas leaking past an injector seal.
Leakage costs rail pressure
Fuel leaving the high-pressure side is fuel the pump must make up. Steady flow from the pressure limiting valve's drain, or an injector over its return-flow limit, keeps rail pressure low. An injector stuck closed takes no fuel and does not lower it.
Programmed, not broken
Some complaints come from ECM settings, not failed parts. A gear-down speed limit holds road speed in the gear below top, and tire revolutions per mile left at the old size make the speedometer read low. Both are read and changed with service software.
Do the meter math
Under a few ohms, subtract the meter leads' own resistance: 1.1 ohms read with leads showing 0.3 ohm is 0.8 ohm. Converting a sensor's voltage to pressure with its scale, then comparing a mechanical gauge, shows when the sensor itself reads low.
05The other content areas
The T2 test has eight content areas. Each has its own page of free questions:
The ASE T2 Diesel Engines practice test page describes the full question bank. How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.
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