Tests.com

If fuel pressure does not increase when the vacuum hose is disconnected from the fuel pressure regulator what could be the causes?

fuel pump is not capable of supplying adequate pressure or the fuel-pressure regulator is defective

Can a spark plug wire routed to close to the MAF sensor signal wire can throw a MAF sensor code?

if a spark plug wire is routed too closely to the signal wire from a mass air flow (MAF) sensor, the induced signal from the ignition wire could create a false MAF signal to the computer.

When doing a starter current draw test, how long should you crank the motor?

15 to 30 seconds of crank time

Which of the following will take place if the fuel filter is installed backwards? a. No change b. Reduced fuel economy c. Lower power under load d. Fuel system pulsation noises

C. When the filter is installed in reverse, the flow is restricted. So, when there is a high demand, such as under load, there will be reduced power.

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

D

Valve adjustment is necessary following the replacement of which of the following components? a. Crankshaft b. Piston c. Balancer d. Cylinder head

D.

If the exhaust system is restricted does pressure increase or decrease in the exhaust?

Increase

True or False. Disconnecting the MAF sensor can reset a learned value?

True

A spark knock will occur if an EGR valve is stuck open or closed?

If the EGR valve is stuck closed a spark knock can occur

An HO2S output voltage is 100-300mV. What does this indicate about the how the motor is running. Rich or lean?

Indicates that the system is operating lean

If air is inserted into a cylinder and it goes through the piston rings. Where will the air end up?

Into the crankcase

When all enabling criteria for a given diagnostic code is met is called?

It is considered a Trip

What is usually the resistance range for a secondary coil?

6k - 30k ohms of resistance

When doing a starter current draw test how much should the battery be charged to?

75%

A restricted return line in the fuel supply system could cause what kind of O2 sensor readings?

A continuous high O2 sensor signal. Rich exhaust or low oxygen content in the exhaust. Results in high HC and CO

What does a lean mixture mean?

A lean air fuel mixture means there is to much Air

What kind of sensor type is an ECT sensor?

Negative coefficient thermistor (NTC). As temperature increases the voltage is decreased.

What does the PCM do when there is a bad fuel mixture?

*When the fuel mixture is Rich the PCM will reduce the amount of fuel used to level it out. *If the fuel mixture is lean the PCM will increase the amount of fuel used to level it out.

At what RPM should you measure vacuum?

2000-2500 RPM

How long should a fuel pump operate with KOEO?

5 Seconds

How much resistance should be between the secondary coil tower?

Between 6000 to 30000 ohms between the 2 points

A technician is doing a power balance test using a scan tool and finds one injector has failed but is still receiving system voltage. Which of the following should be checked? a. Voltage drop of the injector ground b. Voltage check at the ignition power feed c. Engine controls ignition relay ground d. Continuity check between the fuse and injectors

A. Adequate power is available to the injector. Most likely the ECM (Engine Control Module) cannot ground the injector, so you do a voltage drop of the ground side of the injector, which is not contributing.

Why does fuel pressure increase when the vacuum hose is removed from the fuel pressure regulator?

When the load is light, the throttle opening is small and the intake manifold vacuum is high (intake manifold pressure low), therefore the fuel pressure will be low because the diaphragm pulls back to allow more fuel to return to the tank and lowers the fuel pressure. When the load is heavy, the throttle is open, allowing more air to enter and the intake manifold vacuum is low (intake manifold pressure high). Therefore, the fuel pressure will be high and needed because the diaphragm will be pushed closed to create more of a restriction to increase the fuel pressure.

A DTC will set when what percentage of deterioration is formed from a catalytic converter?

When the rear O2 sensor signal reaches approximately 75% of the front O2 sensor signal

Fuel pump with a defective check valve can cause loss of fuel pressure when the engine is shut off?

a defective fuel pump check valve will cause a rapid leak down when the pressure is removed.

A fuel injector is leaking. When the vehicle is shut off will the fuel pressure drop rapidly or not?

a leaking fuel injector will cause the fuel pressure to drop rapidly when the pressure is taken away when the engine is shut off.

In regards to HC (hydrocarbon) and CO (carbon monoxide), will a motor thats misfiring increase or decrease these gases?

A misfiring motor will increase HC and CO readings

What does a rich mixture mean?

A rich air fuel mixture means there is to much fuel.

An engine blows black smoke with little or no power and a DTC (Diagnostic Trouble Code) set. Which of the following is the MOST likely cause? a. Clogged air filter b. Defective EGR valve c. Defective intake manifold gasket d. Leaking exhaust manifold

A. A clogged air filter is the only answer that would reduce the air intake resulting in black smoke and reduced power.

A technician should Inspect all spark plugs for wear by first checking the condition of the center electrode. As a spark plug wears, the center electrode becomes which of the following? a. rounded b. shorter c. whiter d. grayer

A. As a spark plug wears, the center electrode becomes rounded. If the center electrode is rounded, higher ignition system voltage is required to fire the spark plug.

A vehicle comes in with the MIL (malfunction indicator light) on with a P0442 (small leak detected in EVAP canister system) diagnostic trouble code stored. Which of the following is the LEAST likely cause? a. Restricted EVAP canister vent line b. Loose gas cap c. Defective EVAP vent or purge solenoid d. Leaking EVAP purge line

A. Diagnostic trouble code P0442 will set for a small leak and A is a restriction on the canister vent line, so it is the least likely cause. The other three choices are all related to EVAP system leaks.

All of the following will cause HC (hydrocarbons) to be too high, EXCEPT: a. Incorrect idle speed b. Wrong ignition timing c. Defective spark plug d. Defective spark plug wire

A. HC is unburned fuel and defective ignition components prevent proper burning and will cause high HC.

A vehicle has lower fuel economy than expected after a recent oil change. Which of the following is the MOST likely cause? a. Too high viscosity oil used b. Filter not changed c. Excess oil added d. Insufficient oil used

A. If too high a viscosity oil is used the engine will have internal resistance.

Technician A says a defective oxygen sensor could cause a rich or lean condition. Technician B says if one cylinder is lean the computer causes all other cylinders to be lean to compensate. Who is right? a. A only b. B only c. Both A and B d. Neither A nor B

A. Technician A is correct because the PCM "senses" rich or lean air-fuel ratios by means of input from the oxygen sensor. Technician B is wrong because when one cylinder is lean, the computer may make all other cylinders richer to compensate.

A technician connects one lead of a DMM (digital multimeter) to the positive (+) terminal of a battery and the other meter lead to the "B" terminal of the starter solenoid and then cranks the engine. During cranking, the voltmeter displays a reading of 878 mV. Technician A says this reading indicates the positive battery cable has very high resistance. Technician B says this reading indicates that the starter armature is defective. Who is right? a. A only b. B only c. Both A and B d. Neither A nor B

A. Technician A is correct because voltage drop should be less than 0.2 volts not 0.878 volts or 878 mV. Technician B is wrong because this test does not test the integrity of the armature, which is done through load testing for current draw.

The starter control circuit voltage drop test is used to test which of the following? a. Wiring and connections b. Field coils c. Commutator d. Starter solenoid and field coil

A. The purpose of voltage drop testing is to look for high resistance. High voltage drops equal high resistance in wiring and connections. There are specific tests for the other components listed.

A 12 volt test light is connected from the negative primary coil terminal to ground on an electronic distributor ignition (DI) system. The light flutters while cranking the engine. A spark tester does not fire when it is connected from the coil secondary wire to ground while cranking the engine. Which of the following is the MOST likely cause? a. Defective ignition coil b. Defective pickup coil c. Defective ignition module d. Defective spark plug

A. The test light going off and on indicates that the ignition coil triggering device is working but the failure of a spark indicates a coil failure.

Which one of the following is a prime source of problems in secondary air systems? a. Water b. Dirt c. Engine oil d. Engine coolant

A. Water is one of the prime sources of problems in these systems. There are two typical causes of water contamination. The first cause is failure of the reed valve to seal due to breakage or loss of temper, allowing water from the exhaust to enter the A.I.V. case. Second, the reed valves can also stick closed, preventing air from getting to the catalyst.

A vacuum gauge used to check exhaust backpressure should be connected to which of the following components? a. Intake manifold b. Exhaust manifold c. Tail pipe d. Catalytic Converter

A. You are checking for exhaust backpressure by measuring engine vacuum.

Two technicians are discussing a starter current draw test. Technician A says to crank the engine for no more than 60 seconds at a time when performing a current draw test. Technician B says, before doing a current draw test, the battery must be sufficiently charged to at least 75% charge. Who is right? a. A only b. B only c. Both A and B d. Neither A nor B

B.

A vehicle comes in with the MIL (malfunction indicator light) on with a P0456 (small leak detected in EVAP canister system) DTC (Diagnostic Trouble Code) stored. Which of the following could be the cause? a. Defective PCM b. Defective purge (vent) solenoid c. High fuel pressure d. Secondary air injection system

B. A defective purge or vent solenoid is one of four possible causes for a P0456 DTC. The other causes are defective or loose fuel cap, EVAP canister broken or hose cracked or loose and engine vacuum leak.

A vehicle fails an HC emission test at idle and 2,500 rpm, and the engine has an acceleration stumble. The HO2S (Heated Oxygen sensor) voltage is 0.1-0.3 volts on a scan tool, and the injector pulse width is high. No DTCs (diagnostic trouble codes) are found. When propane is directed into the air intake, the O2S sensor voltage immediately increases, and the injector pulse width decreases. The MOST likely cause of this problem is: a. Defective O2S sensor b.. Low fuel pump pressure c. Defective PCM (Powertrain Control Module) d. Opening in the O2S sensor signal wire

B. Low fuel pump pressure is right because this is a lean air-fuel mixture that causes misfire resulting in high HC (hydrocarbon emissions).

Low-firing voltages are measured on a shop oscilloscope and this indicates a lower voltage is required for the spark to jump the gap. Which of the following is the MOST likely cause? a. Lean air/fuel mixture b. Rich air/fuel mixture c. Wide or worn spark plugs d. Bad plug wires

B. Low-firing voltages indicate that less voltage than normal is required to have the spark jump the gap on the spark plug. Lower firing voltages normally occur when resistance is decreased, such as when a spark plug gap is decreased or the air/fuel mixture is excessively rich.

Which of the following would cause the CO (Carbon Monoxide) to be too high? a. Wrong ignition timing b. Defective spark plug c. Defective spark plug wire d. High fuel pump pressure

D. High fuel pump pressure allows over fueling, which cannot be converted to harmless gases. The other three choices will affect HC or Hydrocarbons.

An ignition system is being checked for a NO Spark condition. Technician A says to turn on the ignition (engine off) and using a DMM (Digital Multimeter) test for battery voltage available at the negative terminal of the ignition coil. Technician B says the DMM reading should fluctuate indicating that the primary coil current is being turned on and off. Who is right? a. A only b. B only c. Both A and B d. Neither A nor B

B. Technician B is correct because as the computer pulses the coil on and off the reading will fluctuate. Technician A is wrong because you check for voltage at the positive terminal.

An engine timing belt that is too tight can make what kind of sound? a. Thumping b. Whining c. Slapping d. None

B. The cogs will make a whining sound.

An engine overheats in city traffic but does not at highway speeds. Technician A says that it could be an issue with the fan shroud, which directs airflow through the radiator. Technician B says to visually inspect all shrouds, ducts, and air dams around the radiator and fan for damaged or missing pieces. Who is right? a. A only b. B only c. Both A and B d. Neither A nor B

C.

A vehicle is being tested for exhaust emissions using a 5-gas analyzer. The test results show high O2 (oxygen) reading of 3.5% with HC of 90 ppm [parts per million] and a CO reading of 0.80%. Which of the following is the MOST likely cause of these readings? a. Lean air/fuel mixture b. Rich air/fuel mixture c. Exhaust leak d. Defective spark plug

C. An exhaust system leak can cause a vehicle to have a high O2 (oxygen) reading of 3.5% with normal HC and CO readings (HC = 90 ppm and CO = 0.80%).

A technician is doing a cylinder power balance test on an engine with a misfire. Disabling a cylinder that is not contributing much power will result in which of the following? a. Higher RPM reading b. Lower RPM reading c. Little (if any) RPM drop d. More engine noise

C. Disabling a cylinder that is not operating correctly will not produce much, if any, rpm drop. Disabling a cylinder that is working properly, however, will produce a larger rpm drop.

Which of the following could cause a vehicle to run poorly after the battery was discharged or disconnected? a. PROM (programmable read only memory) failed b. EPROM (erasable programmable read only memory) failed c. Learned value has been lost from RAM d. Learned value has been lost from ROM

C. If battery power is lost the learned value from the RAM may be lost. RAM data is electronically retained which means that it is always to some extent volatile; that is, data storage could be described as temporary - if the circuit is opened, RAM data is lost.

During an injector power balance test, a technician finds one injector has failed but is receiving a good power supply. What should be done next? a. Voltage drop of the injector ground b. Voltage check at the ignition power feed c. Continuity check between PCM and injector d. Continuity check between fuse and injectors

C. The recommendation by most ESM is to do a continuity check between the PCM and injectors, when adequate power is available to the injector.

If there is a crack in a coil, or a spark plug, or a defective spark plug wire, the spark may be visible at night. Which of the following methods is used to locate this spark leak? a. Infrared Black light b. Digital Multimeter probing of spark plug wire c. Test light probing of spark plug wire d. Apply a water mist under load

D. A blue glow or "corona" around the shell of the spark plug is normal and not an indication of a defective spark plug. Use a spray bottle to apply a water mist to the spark plugs, distributor cap and spark plug wires.

The plastic sensors on a computer controlled EGR (Exhaust Gas Recirculation) valve have melted. Which of the following is the LEAST likely cause? a. Excessive exhaust back pressure b. Clogged exhaust system c. Clogged catalytic converter d. Defective EGR valve

D. An EGR valve itself is the least likely cause because excessive back pressure, such as could be caused by a partially clogged exhaust system or clogged catalytic converter, could cause the plastic sensors on the EGR valve to melt. You always check for a restricted exhaust whenever replacing a failed EGR valve sensor.

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

D. As 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.

True or False. The ECT starts off as a poor ground and as temperature increases the ground gets better?

False. starts off as a poor ground and when the temperature rises the ground gets better.

Will a clogged PCV valve cause a rough idle?

If clogged there would be insufficient air for idle and the idle could be rough.

Low fuel pump pressure, a clogged fuel filter or a restricted fuel injector will cause a rich or lean air-fuel mixture?

Lean air-fuel mixture

Will vacuum increase or decrease in the manifold when there is an exhaust restriction?

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

On a OBDII system what are pin 4 and 16 used for?

Pin 4 = Ground Pin 16 = Power

In relation to an EGR valve what will a stuck open EGR valve do to the engine driveability?

Rough idle, engine surge, and stalling

What is the purpose of the EGR valve?

The EGR routes exhaust gas back into the cylinders in order to reduce NOx (nitrogen of oxide)

Does the PCV valve have a direct or in-direct effect on the air/fuel mixture?

The PCV valve is a non electronic component that has an indirect effect to the air/fuel mixture

If you remove the vacuum hose from the fuel pressure regulator will the fuel pressure increase or decrease?

The fuel pressure will increase if the vacuum hose is removed

When is the purpose of a voltage drop test on a starter?

The purpose of the voltage test is to look for high resistance in the wires

What is the rear O2 sensor used for on a PCM?

The rear O2 sensor (downstream) is used strictly for diagnostic purposes. The PCM compares the downstream and the upstream readings to determine convertor efficiency

On-Board self diagnostics test mode should be conducted on a cold or warm engine?

The self-diagnostic procedure should be conducted on a warm engine. (operating temperature or closed loop)

A 3-wire MAF sensor has a poor ground. What kind of sensor readings will it show and what will the fuel mixture look like?

The sensor voltage readings would show high and cause a rich air fuel mixture.