ASE A1 general engine diagnosis practice questions.

Five free practice questions on general engine diagnosis: content area A of the ASE A1 Engine Repair test, 18 of its 45 scored questions (40%). They are in the ASE format: four options, one best answer. Answer each one before opening the explanation. No account, no email.

01The questions

1. Recall · General Engine Diagnosis

   A knock has been traced to the front cylinder on one bank of a V6. Before the technician records it as cylinder 1 and orders parts, why is the cylinder numbering checked in the service information?

   1. Replacing a timing chain renumbers them
   2. Cylinder numbers change with the firing order
   3. Mounting it sideways renumbers them
   4. Makers number V-engine cylinders differently
   Show the answer

   D. Correct. Manufacturers number V-engine cylinders in different ways, some alternating from bank to bank and some running down one bank first, and cylinder 1 is not at the same corner on every engine. The service information's numbering diagram ties a physical location to a number, so the right parts and records follow.

   Why not the others

   A. A timing chain repair does not change how the cylinders are numbered; the numbering is fixed by the engine's design. It is checked because makers number V-engine cylinders differently.

   B. The firing order is the sequence in which the numbered cylinders fire; it does not change which cylinder carries which number. Only the maker's numbering diagram shows which physical cylinder is cylinder 1.

   C. Turning an engine sideways in a vehicle changes where its cylinders sit relative to the vehicle, not the numbers its maker gave them. The numbering is checked because makers number V-engine cylinders differently, and only their diagram ties a number to a location.

2. Recall · General Engine Diagnosis

   A drip under the front of a vehicle is reddish-pink. Why does the technician confirm the fluid by its smell, its feel and which reservoir level is dropping, instead of by its color alone?

   1. Several fluids can share the same color
   2. All fluids turn the same brown with age
   3. Drip color changes with the outside temperature
   4. Leak-detection dye turns every fluid red
   Show the answer

   A. Correct. Makers dye coolants, transmission fluids and other fluids in overlapping colors, and some coolants are the same reddish-pink as many transmission fluids. Smell, feel and the dropping reservoir level identify the fluid, which tells the technician which system to inspect.

   Why not the others

   B. Fluids do darken with age, but that is not why a reddish-pink drip is unclear; fresh coolant and fresh transmission fluid can be dyed the same color.

   C. Temperature does not change a fluid's dye color. Color is unreliable because fluids from different systems, such as some coolants and transmission fluids, are dyed in similar colors.

   D. Fluorescent tracer dyes are added for ultraviolet inspection and do not turn fluids red. Color misleads because fluids from different systems can share the same dye color.

3. EXCEPT · General Engine Diagnosis

   Any of these could cause blue smoke from the exhaust of a turbocharged gasoline engine EXCEPT:

   1. worn piston oil control rings.
   2. a leaking turbocharger shaft seal.
   3. plugged oil drain-back holes in the head.
   4. a fuel injector stuck partly open.
   Show the answer

   D. Correct. An injector stuck open floods its cylinder with extra fuel, which burns incompletely as black smoke, not blue. Blue smoke means engine oil is burning, as it does with worn oil control rings, a leaking turbocharger seal or oil pooled in the head.

   Why not the others

   A. Rings that no longer scrape oil from the cylinder walls leave it to burn in the combustion chamber, which makes blue smoke, so they could be the cause.

   B. A worn turbocharger shaft seal lets oil from the bearing housing into the intake air or the exhaust, where it burns or vaporizes as blue smoke, so it could be the cause.

   C. When the head's drain-back holes plug, oil pools around the valve guides and is drawn down them into the cylinders, where it burns as blue smoke, so it could be the cause.

4. Recall · General Engine Diagnosis

   A relative compression test records starter current on a lab scope while the engine cranks with fuel disabled, and the current peaks are uneven. What else lets the technician tell which peak belongs to which cylinder?

   1. Triggering the scope on the tallest current peak
   2. A second current clamp on the other battery cable
   3. A DMM reading battery voltage while cranking
   4. A cylinder 1 reference on a second channel
   Show the answer

   D. Correct. A second channel tied to cylinder 1, such as its ignition trigger or a pressure transducer in its spark plug hole, marks which current peak is cylinder 1. Counting the following peaks in firing order then names each cylinder.

   Why not the others

   A. The tallest peak belongs to whichever cylinder has the highest compression, which need not be cylinder 1, so triggering on it identifies nothing. A cylinder 1 reference on a second channel is needed.

   B. Both battery cables carry the same starter current, so a second clamp only repeats the same trace. A cylinder 1 reference on another channel is what identifies the peaks.

   C. Battery voltage dips with each compression stroke, but that is the same information as the current trace, and nothing in a voltage reading ties a dip to a cylinder. It cannot say which cylinder made which peak.

5. Diagnosis · General Engine Diagnosis

   At warm idle, the oil filler cap of an engine is hard to pull off, and a gauge at the dipstick tube reads 28 in.H2O of crankcase vacuum. The manufacturer specifies 1 to 5 in.H2O of vacuum at idle. Which of these could be the cause?

   1. Worn piston rings and cylinder walls
   2. A PCV valve stuck in the closed position
   3. A plugged fresh-air breather filter
   4. A PCV hose split between valve and manifold
   Show the answer

   C. Correct. The PCV valve keeps drawing gases out of the crankcase, and with the fresh-air inlet plugged nothing replaces them, so crankcase vacuum climbs far above specification. Strong crankcase vacuum can draw dirt and air in past seals; clean or replace the breather and retest.

   Why not the others

   A. Worn rings add blowby, which pushes crankcase pressure up and reduces vacuum. They cannot produce 28 in.H2O of vacuum.

   B. A PCV valve stuck closed stops the manifold from drawing on the crankcase, so blowby builds pressure rather than vacuum. Strong vacuum means air is being drawn out but not let back in.

   D. A split hose downstream of the PCV valve lets outside air into the hose, weakening the pull on the crankcase so its vacuum drops. The reading is far above specification, so the crankcase is being starved of fresh air.

02Answer key

03What area A covers

This content area is about finding what is wrong with an engine before anything comes apart. It covers verifying the complaint, using service information, sorting engine mechanical faults from other systems, tracing leaks, noises, smoke and fluid loss, and the tests that judge cylinder sealing: manifold vacuum, power balance, compression, cylinder leakage and crankcase ventilation checks, plus lab scope, DMM and scan tool work.

The ASE test specification calls this content area “General Engine Diagnosis”. It carries 18 of the 45 scored questions, 40% of the test.

• Verify the complaint and check service information
• Decide whether a no-start is engine mechanical
• Trace fluid leaks, engine noises and vibrations
• Diagnose oil and coolant use and exhaust smoke
• Read manifold vacuum and boost gauge results
• Run power balance, compression and leakage tests
• Test the PCV system and crankcase pressure
• Use a lab scope, DMM and scan tool

04What the questions turn on

Fast cranking means lost compression

Fast, even cranking with spark, fuel pressure and injector pulses all present points to lost compression, such as a broken timing belt. One burned valve only gives a steady miss, because a no-start needs a fault that affects the whole engine.

Wet and dry compression readings

Oil squirted into a weak cylinder can seal the rings against the wall, but not a valve face. A large rise on the wet test points to the rings or bore; a burned valve leaves the wet reading almost as low as the dry one.

Smoke color names the fluid

Blue smoke means oil is burning, from worn oil control rings, a leaking turbocharger seal or oil pooled in the head; an injector stuck open gives black smoke instead. A brief blue puff after an overnight sit points to worn valve stem seals.

Reading the vacuum needle

The needle's pattern matters. A steady but low idle reading can come from late cam timing, a drop at a regular rhythm from a burned valve, and an occasional drop at no fixed interval from a valve that sometimes sticks open.

05The other content areas

The A1 test has five content areas. Each has its own page of free questions:

The ASE A1 Engine Repair 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.

ToolboxPrep is an independent study site. It is not affiliated with or endorsed by ASE (the National Institute for Automotive Service Excellence). Our questions are original practice questions written to the published ASE test specifications; they are not actual test questions.