Five ASE A1 Engine Repair practice test questions, answers included.

1. Recall · General Engine Diagnosis

   A pickup is driven in with a loud knock that started after its low oil pressure warning flickered. Before road testing it to verify the complaint, the technician checks the oil level and watches the oil pressure reading at idle. Why?

   1. Driving it short of oil can add bearing damage
   2. Low oil makes the knock sensor retard timing
   3. A full crankcase makes the knock easier to hear
   4. The oil life monitor must be reset first
   Show the answer

   A. Correct. A knock that began with a low-pressure warning may mean the bearings are already being starved, and driving with low oil or low pressure can quickly turn a repairable fault into a ruined engine. If the level or pressure is low, the road test waits until the cause is found.

   Why not the others

   B. A knock sensor responds to vibration in the block, not to the oil level. The check is made so an engine that may be starved of oil is not driven and damaged further.

   C. The oil level is not checked to change how loud the knock is. The check protects an engine that may be short of oil from more bearing damage on the road test.

   D. The oil life monitor is reset after an oil change and has nothing to do with verifying a knock. The check protects an engine that may be short of oil from further bearing damage on the road test.

2. Recall · General Engine Diagnosis

   During a closed-throttle coast-down from highway speed, a healthy engine's manifold vacuum reads higher than its warm idle reading. Why?

   1. Exhaust backpressure falls to zero while coasting
   2. The PCM opens the idle air passage wider while coasting
   3. The EGR valve opens fully while the vehicle coasts
   4. Vehicle momentum spins the engine above idle speed
   Show the answer

   D. Correct. With the throttle closed, the vehicle's momentum turns the crankshaft well above idle speed, so the pistons draw on the manifold more often while the closed plate admits very little air. Vacuum climbs above the idle reading until engine speed falls.

   Why not the others

   A. Exhaust backpressure does not fall to zero while the engine turns, and it is not what raises manifold vacuum here. Vacuum rises because the pistons pull harder against the closed throttle at the higher speed.

   B. Letting more air into the manifold would lower vacuum, not raise it. The rise comes from the higher engine speed pulling against the closed throttle.

   C. Exhaust gas admitted to the manifold raises manifold pressure and lowers vacuum, and EGR is not used at closed throttle. The rise comes from the engine being spun faster against the closed throttle.

3. Recall · Cylinder Head and Valve Train Diagnosis and Repair

   A technician is checking a cleaned aluminum cylinder head for warpage before it goes back on the engine. Which of these is the correct check?

   1. A straightedge and feeler gauges laid across the deck
   2. Dye penetrant sprayed on the deck, wiped off and developed
   3. A pressure test of the water jackets with the passages sealed
   4. A micrometer reading of the head's height at each corner
   Show the answer

   A. Correct. Warpage is a bow or twist in the deck, so a precision straightedge is laid lengthwise, crosswise and diagonally and the thickest feeler gauge that slides under it is compared with the manufacturer's flatness limit. A head past the limit is resurfaced, if the manufacturer allows it and the head stays above its minimum height, or replaced.

   Why not the others

   B. Dye penetrant shows surface cracks as colored lines; it says nothing about whether the deck is flat. Flatness is checked with a straightedge and feeler gauge across the deck in several directions.

   C. Pressure testing finds cracks and porosity that leak coolant, not a deck that has bowed. Warpage is measured with a straightedge and feeler gauge laid across the deck in several directions.

   D. A head that bows keeps the same thickness, so corner heights do not show warpage; head height is compared with the manufacturer's minimum after resurfacing. Flatness is checked with a straightedge and feeler gauge.

4. Recall · Lubrication and Cooling Systems Diagnosis and Repair

   On an engine with a fixed-displacement oil pump, a mechanical gauge reads lower oil pressure at the same idle speed once the engine is fully warm than it did just after a cold start. Why?

   1. The filter bypass valve opens once the oil is fully warm
   2. The relief valve opens wider as the oil temperature rises
   3. The thinner hot oil escapes the bearings faster
   4. The oil level falls as warm oil fills the upper engine
   Show the answer

   C. Correct. Oil viscosity drops as it heats, so at the same pump speed more oil flows out through the bearing and lifter clearances and less pressure builds in the galleries. That is why oil pressure specifications state the engine temperature and rpm they apply to.

   Why not the others

   A. The filter bypass valve opens on a high pressure difference across the filter, which happens mostly with cold, thick oil or a clogged element, not with warm oil. Warm oil reads lower because it is thinner.

   B. The relief valve responds to pressure, not temperature. Cold, thick oil raises pressure and is when the valve is most likely to be open; warm oil reads lower because it leaks off through the bearings more easily.

   D. Oil drains back to the pan continuously, and at a correct level the pickup stays covered, so the oil held in the upper engine does not starve the pump. The lower warm reading comes from thinner oil leaking through the bearing clearances.

5. EXCEPT · Fuel, Electrical, Ignition, Air Induction and Exhaust Systems Diagnosis and Service

   A piston removed from an engine has a hole melted through the center of its crown. Any of these could have caused the damage EXCEPT:

   1. a lean mixture from a restricted injector.
   2. ignition timing advanced past specification.
   3. a spark plug of a hotter heat range than specified.
   4. a rich mixture from a leaking injector.
   Show the answer

   D. Correct. Extra fuel cools the combustion chamber, so a rich mixture fouls plugs and dilutes the oil but does not melt a piston. Holes in a crown come from excess heat: a lean mixture, overadvanced timing, or a plug hot enough to cause pre-ignition.

   Why not the others

   A. A lean mixture burns hotter and is prone to detonation, and a cylinder starved by a restricted injector can run hot enough to melt its piston. That is a real cause, so it is not the exception.

   B. Timing advanced too far drives cylinder pressure and temperature up and invites detonation, which can erode and hole a piston crown. That is a genuine cause.

   C. A plug too hot for the engine can let its tip glow and light the charge before the spark (pre-ignition), and the heat this builds can melt a hole in the piston. That is a genuine cause.

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