Fuel Injection part1

Need to find out the purpose and how they work of the following components...

ECU - electronic control unit

The ECU is an electronic unit that controls all things electronic in your engine from how much fuel is being injected to ingnition timing. They are connected to all sensors such as ones below. It then absorbs all that information and makes the car run to the best of its ability with things such as fuel effinacy and firing times.


Mass air flow sensor?

Differant types of mass air flow sensors

This sensor is there to measure how much air is goin into the cylinder so that the ECU can then deliver the correct amount of fuel into the cylinder with the air. All these sensors have a built in intake air temputure senor which is also there to help work out an acurate reading of the mass air flow.


Air Temp sensor?
http://www.youtube.com/watch?v=dM4zUa9-Ib4&feature=fvwrel here is a video that describes the operation of  the Air Temp sensor. The purpose of an air temperature sensor is to help the computer calculate air density. A change in temperature changes the resistance in the sensor. Simply stated, the higher the air temperature gets the less dense the air becomes. As the air becomes less dense the computer knows that it needs to lessen the fuel flow.


TPS - throttle postion sensor?
http://www.youtube.com/watch?v=vyxNLrCMk3I here is a video the explains how a TPS works and a few of the advantages and disadvantages. This sensor is there to moniter the position of the throttle. the sensor is usally a potentiometer (three terminal resistor with a sliding contact which creates a adjustable voltage divider) which provides a variable resistance depending on the position of the valve.

 

Throttle body?

In older engines the throttle body is the body of the carb which has all the air flow go through. In fuel injected engines it is part of the air intake system which controls the amount of air going into your engine.

Carburetor

The components of a basic carb....

How does a carb work?
A carb is the component that mixes the air and fuel together before entering the cylinder to the correct amount so the enigine will fire. The air and fuel are brought into the carb at differant points. Air which is being sucked through the carb is caused by the low atmospheric pressure in the cylinder which causes the air to be pulled from outside the engine. The fuel enters through a jet in the centre of the venturi which is also dependent on the amount of atmospheric pressure inside the carb which is all controlled by the amount of throttle that is being used or how far the throttle butterfly is open. This is a video with a basic explanation: http://www.youtube.com/watch?v=zUuVQfvWSnI

What are the holes in the emulsion tube for and how does it work?
The emulsion tube is a main jet with holes in it. It is used to keep the air fuel mix ratio more uniform as the throttle butterfly is opened.

What is the purpose of the float in the carb?
The float is situated in a chamber where the fuel is pump into from the fuel tank where it will be before getting sucked into the venturi of your carb. Its main purpose is to keep a constant fuel level inside the chamber. It needs to have a constant level as if there is to much fuel your engine will run rich and to little the engine will run lean.

How does the manual choke and automatic choke work?
http://www.youtube.com/watch?v=k-SxQzvCw3U a quick viedo on a thermostatic auto choke.
There are two ways these automatic chokes can be operated: by the heat of the cooling system or exhaust or by the heating effect of and electric current. When your engine is cold there is a bimetal spring situated in the carb connected to the choke butterfly which is wound up tightly which is holding the butterly closed. Once there is heat from either type, the spring will slowly unwind until the buttterfly is open. A manual choke is a lever connected to the choke shaft that has the butterfly on it and when you pull or push the lever it will open and close the butterfly.

Vaccum fuel pump

How does a vacuum fuel pump work on a two stroke engine?
The vaccum fuel pump is bolted to the crankcase of your 2 stroke which is connected to all your carbs individually. It works on the effects of atmospehric pressure inside the cylinder. The diaphram inside the pump will be pulled open from the pressure created in the cylinder which will cause it to open the inlet jet for fuel to enter the fuel chamber which also will create atmospehric pressure in the supply line that will pull the fuel up to the pump from the tank. When trying to crank your engine over these pumps have very low pumping pressure so you need to have a prime buld in the supply line which you manually pump to fill the carb only for starting.

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mechanical lift pump

What is the purpose and how does mechanical lift pump work?
The purpose of a mechanical fuel pump is to pump gas from the fuel tank to the carb. This type of pump has a lever that is hitting one of the lobes on your camshaft. This lever will go up and down as it hits the lobe causing a vaccum effect with the diaphram. This causing a low pressure in the supply line which causes fuel to be drawn up from the fuel tank.

What pressures would you get from these types of pump?
2 - 5 PSI

What does S.I mean?
Spark ignition - petrol  where the initiation of the combustion process of the air-fuel mixture is ignited within the combustion chamber by a spark from a spark plug.

What does C.I mean?
Compression ignition - diesel uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber.

What is the four stroke cycle?
-intake
-compression
-power
-exhaust

How does a bimetallic spring work in a automatic choke work?
The bimetallic spring is a temputure sensitive spring that is attached to the choke butterfly. When the spring heats up the spring will unwind which in turn opens the choke. This video show the spring being heated up and unwinding. http://www.youtube.com/watch?v=7suzzg1kZgY. The bimetal spring may be located in a well in the intake manifold where it is heated by exhaust gases flowing through the crossover passage, or it may be located inside a plastic housing on the carburetor itself.
The choke housing may be heated one of three ways: by hot air siphoned up through a pipe in the exhaust manifold that then flows through the housing and enters the carburetor, by an electrically heated element inside the housing, or by engine coolant circulating through a hose attached to the housing.

What is the purpose of the venturi and how does it work?

The venturi is where the air and fuel mix mets in the carburetor. The start of the venturi is alot wider than the centre of it as the picture too the left shows. When the airflow from the atmosphere rushes through the carb it is forced to speed up as the venturis width gets smaller. This creates a low pressure where the fuel now enters the carb and mixes with the air.


How is the idle and mixture screw adjusted?
This screw adjusts the throttle butterfly position at idle which in turn raises or lowers the engines RPM. It does not control the air fuel ratio. When you are adjusting it you will turn the screw clockwise to open the throttle butterfly if the revs are to low and the oppisite if the revs are to manufacturers specs.


How do you adjust the float in the carburetor?

To adjust the float you will need to firstly take the carb off the intake system and dismantle so you can access the float in its chamber. If you turn the chamber upside down with the float still in there it will hold the float where the full will hold it when the chamber is full of fuel. You should check the gap between the metal bracket and the top of the float againest manufactures specs. If adjustment needed you will just need to bend the bracket until sitting correctly.


An engine lacks power. What is the likely problem?
There are many differant resons an engine will be lacking power but to do with the carb there is only a few differant things that can cause this. Firstly if any of the fuel jets are blocked you will lack power as the fuel air mix will be to lean. Also if the air isnt sufficent the mix will also be too lean.

Explain how a fuel cut off solenoid is checked and why is it fitted?

This solenoid is fitted to stop the flow of fuel once the ignition has been turned off. When the ignition is turned on the solenoid will open the fuel passage so fuel can get to the engine. Once the ignition is turned off the solenoid loses power and shuts this passage. To check them you need to put power to it and if itll open its working fine.

When dismantling a carb what precaution should you take?
First of all always take note of where everything came from and always mark things that should be marked such as the way the housings go together etc. Never turn the carb upside down if your not fully dismantling it. and make sure your work area is always tidy as carbs have very samll components which can be lost easily.

referances:
www.google.com/images
www.wikipedia.com
www.howstuffworks.com
Ed May books Vol 1 & 2