This is copied from 'Training Workbook - Maestro'
For the curious ones amongst you, here is the quiz!
QUIZ
OVERVIEW
It is based on the HIF design and is know as the HIF 44E with fuel economy and efficient warm up in mind we have incorporated two important new features on the carburettor, a fuel cut off valve and an automatic enrichment device.
They are both controlled by the electronic control unit or ECU as it is known.
the ECU receives information from a number of sources, engine temperature, ambient temperature, accelerator pedal position and engine speed.
Engine temperature is sensed by the thermistor on the on the left, mounted on the engine block, ambient air temperature is sensed by a thermistor behind the right hand headlamp
A switch on the accelarator tells the ECU whenever the drivers foot is off the pedal, engine speed data is taken from the ignition system
The ECU gathers all this information to ensure correct functioning of the cut off valve and the automatic enrichment, let us see how the fuel cut-off valve works
FUEL CUT OFF VALVE
It is a fuel economy device which operates under certain conditions during overrun.
These are:
Whenever the valve operates, venturi depression is introduced into the float chamber, the reducing the amount of fuel that can be drawn from the jet. Valve operation is not continuos, it pulses at a rate of 1/2 second on 1/2 second off. this ensures the engine will pick up smoothly when the driver accelerates.
AUTOMATIC ENRICHMENT (CHOKE)
Now the automatic enrichment. It controls the air/fuel mixture and fast idle during cold start up and warm conditions, lets see how its works.
The ECU sends information the the stepper motor, a stepper motor is a device which converts electrical pulses into small mechanical turning movements
The stepper motor is connected to a rotary valve located in the fuel supply within the carburettor. Depending on the signal received by the stepper motor from the ECU, it will turn the valve one way or the other to richen or weaken the mixture. it does this in a series of 'steps' of 7 1/2 o
Attached to the enrichment spindle is a cam, which operates a throttle jack to give the necessary fast idle during cold starts. The throttle jack will also operate to speed up the engine if the engine is loaded and idle speed falls below its norm
ADJUSTMENTS
Now carburettor adjustments. Run the engine to normal operating temperature, then make sure there is some play at the lost motion link and that there is clearance between the fast idle screw and the throttle jack
Adjust the idle speed; 650rpm for the 1.6 engine 750rpm for the 1.3's, except the HLE model which is 625rpm
Incidentally if you reduce the idle speed to more than approximately 100 rpm towards its correct level, the throttle jack will be triggered automatically by the ECU. The engine will then speed up to give you a false idle RPM, and you will have to wait for approximately 2 minutes to allow the system to return to normal
Next adjust the mixture screw to give a CO reading of 2.5% + or - 1%
With the idle speed and the mixture correctly set you can now adjust the fast idle. But you must isolate certain sensors to the ECU to avoid a false setting
Do this by removing the ambient temperature sensor and join the two connectors
You must disconnect the coolant sensor and fit a resistor across the plug, the value of the resistor varies from model to model, so check your repair operation manual for details
When the sensors are isolated, the throttle jack is activated to fast idle condition. The fast idle should be 1100rpm on 1300 engines and 1000 rpm on 1600 engines. if it is not, adjust the fast idle screw, then restore the sensors to their normal condition
Finally adjust the lost motion link gap to 1.5mm + or - 0.25mm. The carburettor adjustments are now complete
Before we finish this section on carburettors, a mention of the MG 1600. twin webbers are fitted, which together with other modifications to the standard 1600 engine are responsible for more than 100 BHP, giving a top speed in excess of 110mph (175kph). You will find complete maintenance and servicing details in your repair operation manual.
Review Quiz No 1
It is based on the HIF design and is know as the HIF 44E with fuel economy and efficient warm up in mind we have incorporated two important new features on the carburettor, a fuel cut off valve and an automatic enrichment device.
They are both controlled by the electronic control unit or ECU as it is known.
the ECU receives information from a number of sources, engine temperature, ambient temperature, accelerator pedal position and engine speed.
Engine temperature is sensed by the thermistor on the on the left, mounted on the engine block, ambient air temperature is sensed by a thermistor behind the right hand headlamp
A switch on the accelarator tells the ECU whenever the drivers foot is off the pedal, engine speed data is taken from the ignition system
The ECU gathers all this information to ensure correct functioning of the cut off valve and the automatic enrichment, let us see how the fuel cut-off valve works
FUEL CUT OFF VALVE
It is a fuel economy device which operates under certain conditions during overrun.
These are:
- Engine Temperature above 80oC
- Ambient air above 6oC
- Engine speed above 1300 rpm
- and a closed throttle
Whenever the valve operates, venturi depression is introduced into the float chamber, the reducing the amount of fuel that can be drawn from the jet. Valve operation is not continuos, it pulses at a rate of 1/2 second on 1/2 second off. this ensures the engine will pick up smoothly when the driver accelerates.
AUTOMATIC ENRICHMENT (CHOKE)
Now the automatic enrichment. It controls the air/fuel mixture and fast idle during cold start up and warm conditions, lets see how its works.
The ECU sends information the the stepper motor, a stepper motor is a device which converts electrical pulses into small mechanical turning movements
The stepper motor is connected to a rotary valve located in the fuel supply within the carburettor. Depending on the signal received by the stepper motor from the ECU, it will turn the valve one way or the other to richen or weaken the mixture. it does this in a series of 'steps' of 7 1/2 o
Attached to the enrichment spindle is a cam, which operates a throttle jack to give the necessary fast idle during cold starts. The throttle jack will also operate to speed up the engine if the engine is loaded and idle speed falls below its norm
ADJUSTMENTS
Now carburettor adjustments. Run the engine to normal operating temperature, then make sure there is some play at the lost motion link and that there is clearance between the fast idle screw and the throttle jack
Adjust the idle speed; 650rpm for the 1.6 engine 750rpm for the 1.3's, except the HLE model which is 625rpm
Incidentally if you reduce the idle speed to more than approximately 100 rpm towards its correct level, the throttle jack will be triggered automatically by the ECU. The engine will then speed up to give you a false idle RPM, and you will have to wait for approximately 2 minutes to allow the system to return to normal
Next adjust the mixture screw to give a CO reading of 2.5% + or - 1%
With the idle speed and the mixture correctly set you can now adjust the fast idle. But you must isolate certain sensors to the ECU to avoid a false setting
Do this by removing the ambient temperature sensor and join the two connectors
You must disconnect the coolant sensor and fit a resistor across the plug, the value of the resistor varies from model to model, so check your repair operation manual for details
When the sensors are isolated, the throttle jack is activated to fast idle condition. The fast idle should be 1100rpm on 1300 engines and 1000 rpm on 1600 engines. if it is not, adjust the fast idle screw, then restore the sensors to their normal condition
Finally adjust the lost motion link gap to 1.5mm + or - 0.25mm. The carburettor adjustments are now complete
Before we finish this section on carburettors, a mention of the MG 1600. twin webbers are fitted, which together with other modifications to the standard 1600 engine are responsible for more than 100 BHP, giving a top speed in excess of 110mph (175kph). You will find complete maintenance and servicing details in your repair operation manual.
Review Quiz No 1
For the curious ones amongst you, here is the quiz!
QUIZ
- On the R series engine, the oil pump is located externally, at the rear (TRUE/FALSE)
- What are the two carburettor settings that the ECU adjusts?
- Name the FOUR sources of information to the ECU
- What is the purpose of the fuel cut off valve?
- Below 1300rpm, the fuel cut off valve will pulse 1/2 second ON, 1/2 second OFF (TRUE/FALSE)
- The throttle jack in the automatic enrichment control is activated by the ECU (TRUE/FALSE)
- When starting to tune the carburettor, why is it necessary to ensure the is clearance between the fast idle screw, and the throttle jack?
- Prior to adjusting the fast idle, you must join the connectors supplying both the ambient temperature and the coolant temperature sensor (TRUE/FALSE)