Practice Questions Flashcards
When the operator performs his pre-op checks in the morning he finds that the top of the rad hose has collapsed. Which of the following can lead to this condition?
A) the thermostat needs to be replaced
B) the coolant viscosity is too high
C) the rad cap is defective
D) the top rad hose needs to be replaced
C… many rad caps have a vacuum valve built into the cap that allows air or coolant to re-enter the rad as the coolant cools, preventing hose collapse
A technician has found that the rad cap is failing to seal properly on a diesel engine and doesn’t hold pressure in the rad. Which of the following would be more likely to occur?
A) lowers coolant’s boiling point
B) lowers operating temp
C) increases hydrocarbon emissions
D) increases operating temperatures
A… a rad cap with no pressure in it will cause the coolant to boil sooner as the boiling point of the coolant is higher when the rad has pressure in it. One psi of pressure increase raises the boiling point of coolant by approx 1.65 degrees Celsius.
A technician is inspecting the crankshaft main journal cheek to the rod journal area and finds radiating cracks have developed in this area. Which of the following could be responsible for these cracks?
A) torsional stress in the crankshaft
B) misalignment of the main bearing bores
C) crankshaft lubrication failure
D) bent connecting rod
A… torsional stress causes excessive twisting to occur in the crankshaft which can lead to cracks developing in the main journal cheeks. Misalignment of the cylinder would not cause torsional vibration to occur in the crankshaft. Crankshaft lubrication failure would cause bearing damage to the crankshaft. Excessively worn rod bearing do not cause torsional vibration but results in lower oil pressure and eventually bearing failure
A technician tests the inlet restriction of a turbo-charged diesel engine at full engine load. What is generally considered the maximum restriction allowed on the suction side of the intake?
A) 25” of mercury
B) 25” of water
C) 25 psi
D) 25 Kpa
B… a manometer calibrated in inches of water is used to measure the negative low pressure restriction on the suction side of the air filter. When the restriction reaches 25” the filter is generally replaced. It’s important to note that the max restriction occurs under max eng loads, not at high engine idle speed
A technician checks a suspected bad injector for back leakage and finds the leakage is higher than normal. Which of the following is likely responsible for this condition?
A) internal nozzle wear
B) low cracking pressure
C) high cracking pressure
D) sticking nozzle assembly
A… only internal nozzle wear wear will cause excess fuel to leak past the nozzle and result in high back leakage. Answer B,C and D will not affect back leakage. Excessive back leakage is caused by wear to the nozzle and body of the nozzle assembly. The only thing that seals this area is the tight running clearances which are in the order of 2 to 5 microns, depending on the nozzle type. This allows for some back leakage to occur for lubrication purposes
A technician is testing a loader for excessive exhaust particulate. Which of the following emissions test instruments uses a light extinction principal to measure particulate?
A) VOC (volatile organic compound analyzer
B) seven gas analyzer
C)two gas analyzer
D) opacity meter
A… The shorter line will result in a quicker pressure rise due to a lower volume of fuel in that line. The pumping capacity of the plunger hasn’t changed; therefore it will reach cracking pressure slightly faster, causing a slight advance to the timing for that cylinder. Response C isn’t correct as cracking pressure is controlled by the spring pressure in the injector, not by length. Response D isn’t correct as the length of line wont increase cracking pressure. The cracking pressure is controlled by the tension of the nozzle spring which is adjustable. The more spring tension is applied the higher the cracking pressure. The fuel pressure must overcome the spring pressure before the fuel can be injected into the combustion chamber
When an emissions test is conducted on a diesel engine that is operating at below normal coolant temperatures, which emissions would likely be elevated due to the low engine operating temperatures?
A) oxides of nitrogen
B) carbon dioxide
C) nitrous oxides
D) hydrocarbons
D… lower than normal operating temp would result in incomplete combustion which would elevate the hydrocarbon levels in exhaust. Oxides of nitrogen and nitrous oxides usually become elevated when combustion chamber temp are too high. Co2 is present in combustion and will not change significantly as a result of temperature changes in the engine
A technician is testing the operation of an aneroid valve on a turbo charged diesel engine. Which of the following does the aneroid valve control?
A) Limits fuel delivery during acceleration to minimize black smoke
B)increases fuel pressure until the engine speed starts to increase
C) is only used at high elevations to compensate for lower air pressure
D) increases turbo-boost pressure during acceleration to minimize smoke
A… the aneroid valve limits the rate of fuel delivery during acceleration with spring pressure opposing boost pressure. Ensuring there is enough air to burn the fuel completely, minimizing the amount of black smoke in the exhaust
What will occur when water enters the fuel circuit of a diesel engine with a secondary fuel filter that is capable of entrapping particulate as small as two microns?
A) the fuel filter will become plugged and reduce fuel flow
B) the fuel filter will likely collapse from injector suction
C) the water will be absorbed into the fuel and burned off
D) the filter media will break down and eventually collapse
A… fuel filters that have a 2 micron rating will not allow water to pass through and will eventually plug up and stop the engine from running. Fuel pressure is regulated with a relief valve and will not get absorbed into the primary fuel circuit. The fuel filters media is built to withstand fuel system pressures and will not collapse
A technician is performing a cylinder leak down test on a diesel engine and notices that air is coming out from the dipstick during the test. Which of the following could be responsible for this?
A) excessive wear on the valve guides
B) excessive wear on the intake valve seats
C) excessive wear on the piston rings
D) excessive wear on exhaust valve seats
C… worn piston rings and cylinder liners will allow air to enter the crankcase and escape out of the dipstick tube. If the intake valve were not sealing properly,air would escape out of the exhaust. Valve guide wear cannot be determined with a cylinder leak down test
A technician is performing a bearing leak down test on a diesel engine. What would excessive oil leakage from one connecting rod bearing journal area indicate?
A) excessively worn connecting rod bearing
B) excessive main bearing endplay
C) excessive rod bearing crush
D) insufficient. Rod journal side clearance
A… excessive oil leakage indicates that the is excessive clearance between the rod journal and the connecting rod bearing. A leak down test would not show excessive end play to the crankshaft, excessive bearing crush or insufficient rod journal side clearance
After a technician has replaced a turbocharger on a diesel engine, which of the following should be performed before the initial startup?
A) a cylinder leakage test must be performed
B) the turbocharger must be primed with oil
C) lube oil pressure test must be performed
D) a cylinder compression test must be performed
B… once the turbocharger is replaced, pour some clean oil into the turbocharger oil inlet and turn the compressor wheel by hand to spread oil on the bearings. A leak down test would not show excessive end play to the crankshaft, excessive bearing crush or insufficient rod journal side clearance
A tech installs a new 15 psi pressure cap on a diesel engine rad. What effect would this have on the coolants boiling point?
A) raised it by 25 degrees
B) lower it by 25 degrees
C) raise it by 8.3 degrees
D) lower it by 8.3 degrees
A… the boiling point of the coolant will increase by 1.66 degrees for every 1 psi of additional pressure in a rad
A technician is going to perform an efficiency test on a turbocharged diesel engine intercooler. Which of the following procedures would he use?
A)measure the air temp drop across the inlet and outlet under load
B) measure the air pressure drop across the inlet and outlet a low idle
C) compare boost pressure readings between full load and high idle
D) measure the inlet restriction from one side to the other with a manometer
A… to determine the efficiency of an air to air aftercooler, the air temp drop between the inlet and outlet of the cooler must be compared to the specifications provided by the engine manufacturer. The main purpose of the air to air intercooler is to lower the air temp of the compressed air. Response B, C or D do not address the temperature difference across the intercooler
