Question 1

Early Motronic idle speed controls are being discussed. Technician A says an idle air bypass device is used to increase idle speed when the engine is cold. Technician B says the rotary idle control valve is used to control idle speed at any engine temperature. Who is correct?

Accepted Answer

Both technicians are correct. Technician A is correct in stating that an idle air bypass device is used to increase idle speed when the engine is cold, which helps the engine run smoothly during warm-up. Technician B is correct in stating that a rotary idle control valve is used to control idle speed at any engine temperature, adjusting the amount of air bypassing the throttle plate to maintain the desired idle speed under various conditions.

Question 2

Which statement regarding air-fuel ratio is correct?

Accepted Answer

Both statements are correct. The ideal air-fuel ratio for complete combustion is known as stoichiometric, and lambda is a dimensionless number that describes the ratio of actual air-fuel mixture to the stoichiometric mixture.

Question 3

Which of the following sensors is commonly used on a Bosch Motronic system to allow the PCM to distinguish between engine misfire and an erratic crankshaft signal caused by rough road surfaces?

Accepted Answer

A chassis accelerometer is used to detect vibrations and movements of the vehicle, which helps the PCM differentiate between engine misfires and vibrations caused by rough road surfaces.

Question 4

A Motronic system controls all of the following EXCEPT for the:

Accepted Answer

A Motronic system typically controls fuel injectors, fuel pump relay, and ignition timing, but not the cold-start injector, which is usually part of older or separate systems.

Question 5

What is the primary advantage of using a cold start fuel injector?

Accepted Answer

The primary advantage of using a cold start fuel injector is that it allows more time for the fuel to vaporize when starting a cold engine. This is important because cold fuels tend to not vaporize well and can cause a rich fuel mixture which leads to engine stalling or rough running. The cold start injector helps to ensure a smoother start by supplying additional fuel directly into the intake manifold during the engine's startup.

Question 6

What is the principal input used by an L-Jetronic system to determine how much fuel to inject?

Accepted Answer

The principal input used by an L-Jetronic system to determine how much fuel to inject is air flow. The system measures the amount of air entering the engine through the air flow sensor and then calculates the appropriate amount of fuel to inject based on that measurement.

Question 7

Which statement about a turbocharged engine Motronic system is correct?

Accepted Answer

Both statements are correct because the Motronic system can use boost pressure reduction and spark retard as methods to control spark knock in turbocharged engines.

Question 8

Which of these inputs is NOT used by the PCM to modify the read-only map for ignition timing?

Accepted Answer

Air flow is not used by the PCM to modify the read-only map for ignition timing.

Question 9

The Motronic system is able to perform "plausibility" test on the MAF sensor. What does this mean?

Accepted Answer

The answer of The Motronic system is able to perform...

Question 10

The Motronic electronic transmission control is being discussed. Technician A says it momentarily retards ignition timing during transmission shifting. Technician B says the PCM controls the automatic transmission's shift points using spool-type shift valves. Who is correct?

Accepted Answer

Technician A is correct because the Motronic system can momentarily retard ignition timing to smooth out shifts. Technician B is incorrect because modern PCM systems use solenoids, not spool-type shift valves, to control shift points.

Question 11

Why does the main power relay on a Bosch Motronic fuel injection system contain a diode?

Accepted Answer

The diode in the main power relay of a Bosch Motronic fuel injection system serves two purposes - to protect the PCM against voltage surges and accidental polarity reversals. Therefore, option D, which includes both purposes, is the correct choice. Option C is incorrect because the diode cannot keep the relay energized in case of relay circuit driver failure within the PCM.

Question 12

The pulse-width control map is being discussed. Technician A says it functions as the look-up table the PCM uses to determine injector pulse width. Technician B says the map values are stored in the PCM's read-only memory and cannot be modified. Who is correct?

Accepted Answer

The pulse-width control map does indeed function as a look-up table for determining injector pulse width, as stated by Technician A. Technician B is also correct in stating that the map values are stored in the PCM's read-only memory, making them unmodifiable under normal circumstances.

Question 13

Cranking mode is being discussed. Technician A says extra injector pulses may be used to richen the mixture. Technician B says an extra injector may be used to richen the mixture. Who is correct?

Accepted Answer

The answer of Cranking mode is being discussed. Technician A...

Question 14

Which of these statements about knock sensors is correct?

Accepted Answer

Knock sensors detect engine knock or pinging and send a voltage signal to the engine control module (ECM).

Question 15

Bosch pulsed multipoint injection systems are being discussed. Technician A says the injectors may be operated sequentially. Technician B says the injectors may be operated in clustered groups. Who is correct?

Accepted Answer

Both technicians are correct. Bosch pulsed multipoint injection systems can be operated either sequentially or in clustered groups.

Question 16

Technician A says that European vehicles may have two data link connectors - an OBD II standardized DLC under the instrument panel and a manufacturer proprietary DLC designed for dealership scan tools. Technician B says that modern European vehicles will have a CAN data bus that will connect with the OBD II DLC. Who is correct?

Accepted Answer

Technician A is correct because many European vehicles do have a manufacturer proprietary DLC that is designed for dealership scan tools. Technician B is also correct because modern European vehicles will have a CAN data bus that connects with the OBD II DLC. Both statements are true.

Question 17

Which feature is unique to the Bosch K-Jetronic injection system?

Accepted Answer

The unique feature of the Bosch K-Jetronic injection system is that the opening of the air valve controls a fuel metering valve. It does not use electronic control of the injectors, sensors to regulate fuel control, or manifold pressure to determine engine load.

Question 18

Motronic fuel systems are being discussed. Technician A says the fuel pump is directly controlled by the PCM. Technician B says some systems use a pulse damper to regulate fuel pressure. Who is correct?

Accepted Answer

The answer of Motronic fuel systems are being discussed. Technician...

Question 19

What is the principal difference between the L-Jetronic and LH-Jetronic systems?

Accepted Answer

The principal difference between the L-Jetronic and LH-Jetronic fuel injection systems is the type of air flow sensor used. The L-Jetronic uses a flapper-type air flow meter, while the LH-Jetronic uses a hot wire air mass meter.

Question 20

The injectors are being serviced on a Bosch fuel injection system. Technician A says the seals often leak and should be inspected carefully any time the injectors are removed. Technician B says petroleum jelly is generally regarded as the best O-ring installation lubricant. Who is correct?

Accepted Answer

Technician A is correct that the seals on the injectors can often develop leaks and should be inspected carefully when the injectors are removed for service. Technician B is incorrect that petroleum jelly is the best O-ring installation lubricant, as it can cause O-rings to swell and potentially lead to leaks. Technicians should use a silicone-based lubricant specifically designed for O-ring installation.

Quiz 15: European Bosch Computerized Engine Controls