General Engine Diagnosis (Tests.com)

Which of the following creates a flapping sound near the front of the engine? a. Timing belt tension too tight b. Drive belt too tight c. Drive belt too loose d. Timing belt tension too loose

A loose timing belt will cause a flapping sound near the front of the engine.

An engine will not start. The technician uses a scan tool and finds the DTC (Diagnostic Trouble Code) P0335 (CKP Crankshaft Position Sensor) stored. This vehicle is using a COP (coil-on-plug) ignition system. Which of the following is the MOST likely cause? a. Bad CKP (Crankshaft Position) Sensor ground b. Defective CMP (Cam Position) Sensor c. Open power circuit to Ignition Coil number 1 d. Abnormal scope pattern

When the crankshaft position sensor (POS) signal is not detected by the ECM during the first few seconds of engine cranking, the ECM will set a code P0335. When the engine cranks, the ECM looks for the engine RPM, which is delivered by the CKP (crankshaft position) sensor. A bad Engine Position Sensor ground will cause the engine not to start and set this code. B is wrong because the DTC (Diagnostic Trouble Code) is for a CKP sensor and the CMP (Cam Position) sensor will not cause this concern. C is wrong because an open power circuit to the coil number one will cause a misfire and set a misfire code.

A vacuum gauge is used to check exhaust backpressure. Where is the gauge hose connected? a. Exhaust manifold b. Intake manifold c. Air cleaner d. Catalytic Converter

When using a vacuum valve to test for exhaust back pressure you connect it to a port on the intake manifold. If the exhaust system is restricted, pressure increases in exhaust. This pressure is called back pressure. Intake manifold vacuum will drop gradually if the engine is kept at a constant speed and the exhaust is restricted. The reason vacuum will drop is that all exhaust leaving the engine at a higher engine speed cannot get through restriction.

An engine cranks but will not start. Which of the following should be checked first? a. Check for spark b. Check for fuel c. Check engine compression d. Check engine timing

Without ignition, an engine will crank but will not start. The other three choices are all possible sources of a no-start when the engine cranks but would not be the first thing a technician should check.

A power balance test is being performed. Technician A says to note the engine RPM before and during the test for each cylinder. Technician B says to record the RPM drop for each cylinder. Who is right? a. A only b. B only c. Both A and B d. Neither A nor B

Both technicians are correct. Tech A is right because engine RPM (Revolutions Per Minute) is an indicator of when that cylinder is contributing to the engine power and if it is balanced. You note the RPM before and during the test so when the cylinder is shorted out you can tell if it changes. Tech B is right because when the engine speed (RPM) does not drop or change, then that cylinder is not having an effect on engine operation or balance.

The engine cranks but will not start. Which of the following is prioritized on a typical symptom flow chart to check before the others? a. Ignition circuit b. Ground circuit c. Camshaft position sensor d. Crankshaft position sensor

On the typical symptom flow chart, the "Ignition Circuit" is listed as a priority 1 item in the order of inspection to check first before the other listed as distracters in this question.

An engine noise sounds like a knock at the side of the engine that is louder when the engine is cold and goes away or is reduced when the engine reaches operating temperature. Which of the following is the MOST likely cause? a. Cam bearing b. Main bearing c. Wrist pin d. Piston slap

Piston slap is a knock heard at the side of the engine which is louder when the engine is cold and goes away or is reduced when the engine reaches operating temperature.

During a cylinder leakage test on an engine cylinder, the technician can hear air coming out the tail pipe. Technician A says this could be caused by a burnt exhaust valve. Technician B says this could indicate that the piston ring gaps were installed in line. Who is right? a. A only b. B only c. Both A and B d. Neither A nor B

Technician A is correct because air put in the cylinder is leaking out a damaged or burnt exhaust valve. Technician B is wrong because if the piston ring gaps were lined up, this might result in oil consumption but any compression leaking would go into the crankcase and would exit through the PCV (positive crankcase ventilation) system. The rings would eventually turn and no longer be lined up.

An engine cranks but will not start and the scan tool shows DTC (Diagnostic Trouble Code) P1320 (Ignition Signal) stored on a vehicle with a distributor-type single ignition coil. What is the next step after verifying the concern? a. Perform an input signal circuit check b. Check for power to the coil c. Check the power transistor's ground circuit d. Perform a power transistor output circuit check

The first step of most diagnostic procedures is to attempt to start the engine. Since the stem states that the engine will not start due to a lack of spark, the next step tells you to check for B+ power to the ignition coil.

his question contains the word EXCEPT. Read the question carefully before choosing your answer. All of the following are true regarding oil dilution, EXCEPT: a. Result of unburned fuel getting into the oil b. Caused by an overly rich air-fuel mixture c. Higher at normal operating temperature d. Minimized by a properly tuned engine

This is the exception because oil dilution occurs at high operating temperatures. Rarely does oil dilute during normal engine temperature unless another chemical is added to the oil.

A cog type timing belt that is tight will make what type of noise? a. Thumping sound b. Whining sound c. Slapping sound d. Will not make noise

When cogs or teeth of the rubber timing belt are tight against the sprockets, they whine the vanes of a siren. The other three choices are not the sound of a cog timing belt.