Fuel System

Theory and background

• The fuel tank holds the petroleum, the petrol is pumped through the fuel filter to the fuel rail with the fuel pump. The petrol is supplied from the fuel rail to each cylinder at the right time by the fuel injectors. The fuel injectors are solenoids that are controlled by the car's CPU. The CPU calculates how much fuel is needed.
• The pressure in the fuel rail is regulated by the Fuel Pressure Regulator. The fuel pressure regulator is controlled by the vacuum in the intake manifold. If there is a high pressure vacuum on the regulator it opens up and redirects some of the fuel back to the fuel tank via the return line. As the load of the engine increases the vacuum decreases closing the regulator which increases the pressure in the fuel line and that increases the amount  and pressure of the fuel that is supplied by the injectors. 

Procedure for experiment 

• With the engine idling we measured the No Load vacuum from the intake manifold to be -11 psi and the Fuel pressure to be 40 psi
• The second test we did was to simulate the engine being Under Load. While the engine was idling we disconnected the vacuum hose from the intake and measured the vacuum to be 0 psi and the Fuel pressure to be 50 psi

Reflection on experiment


If the engines revs increase the vacuum in the manifold gets less so the regulator allows less fuel to run back to the tank and it also increases the fuel pressure in the fuel line which forces more fuel through the injectors at a higher pressure.

Off car starter testing

Testing

1. Armature

Test the armature by connecting the multimeter (on the ohm setting) between the commutator (Where the brushes run on). This should give the resistance of the coils/field windings inside the armature. Check the reading against the specifications given. To test if there is a short circuit between the coils and the body of the armature connect the multimeter's negative to the body and the positive to the commutator, the reading should be infinity. If it does give a ohm reading it means that there is a shortage inside the armature.

     2. Field coils

The field coils are tested in a similar way as the armature's coils. Set the multimeter to ohms and connect it to the terminals of the field windings, check the readings against the specifications. A short circuit can also be checked by connecting on of the multimeter's wires on the coil terminals and the other on the body of the starter, the reading should show infinity. If not it means there is a short. Some starters have fixed magnets instead of field coils. The disadvantage is that the magnets can become demagnetized, the coils are more durable.

 Starter with permanent magnets

     3. Brushes

The brushes should be measured using a vernier caliper. The reading should at least be bigger than the minimum specified value, if not then they need replacing. Another thing that needs to be checked is the commutator that brushes runs on. If it is burned black it needs to be cleaned using a fine grade sand paper. If the surface of the commutator is damaged it will need to be skimmed using a lathe or be replaced.

Commutator end bracket

    4. Solenoid

To test the terminals inside the solenoid connect the multimeter to the two terminals on the outside of the solenoid using the ohm setting. Push the plunger fully in if there is no reading on the multimeter it means that the terminals are not being connected and will need servicing. To test if the solenoid works connect the negative wire from a power supply to the body of the solenoid and a positive wire to the terminal on the solenoid that connects to the ignition. The plunger should be pulled back by the solenoid if not it means that it is faulty

Testing solenoid terminals

    5. Clutch and bearings

The pinion should move freely in one direction and move with the motor in another direction. The clutch is not working if the gear turns with the motor or freely in both directions. To check the bearing you can rotate them with your fingers if they move smoothly they are fine. The bearings should also be checked for any oil leaks and any damage.

Clutch and pinion gear

On car starter test

Battery test

check that the battery is charged and that it is working properly by testing its volts or test it using a hydrometer

then disconnect the fuel system or ignition system by unplugging the fuel pump or the distributor.

Crank the engine while the multimeter is connected. The voltage should not drop under 9.5 volts

Voltage drop test

Use the multimeter to determine the voltage drop between the negative terminal of the battery and the starter motor's body. Then check the voltage drop between the battery's positive terminal and the starter's terminals

Starter Motor

Parts

• Pinions Gear (clutch)
• Armature
• Solenoid (Contacts)
• Plunger
• Leaver
• Field windings (pole shoes)

Functions

• The pinions gear connects the motor to the fly wheel
• Soleniod  pulls the plunger back using a magnetic field
• The plunger is connected to the engagement lever. If the solenoid is activated the plunger is pulled back pulling the lever back and that pushes the pinion gear forward so that it engages to the fly wheel. The plunger also acts as a switch, when it pulls back it connect the power to the motor.
• The field winding creates a magnetic field the interacts with the armature
• The armature is the pole piece for the magnet, it directs the magnetic fields toward the field windings

Off car alternator test

Parts

• Regulator
• Rectifier
• Rotor
• Stator
• Brushes
• Slip rings

Function

• Slip rings and brushes are used to supply power to moving parts. The slip rings act as rails for the brushes to run on so that the electrical power can be transferred from the stationary regulator to the moving rotor shaft.
• Regulator controls the strength of the rotor. The rotor is an electromagnet, the strength of the magnet is controlled by the regulator changing the magnets input voltage.
• The stator consists of copper coils that surrounds the rotor. The rotation of the rotor causes an induced voltage in the copper coils. The voltage created is AC 
• The Rectifiers convert the the AC voltage into DC voltage so that it may be stored by the battery.

Reason for using alternators

DC generators have moving coils inside a magnetic field. The engine's speed is to fast for the DC generators to handle, the centripetal force pulls it apart. The AC alternators have the magnet in side of the coils. The magnets have a higher tolerance for the centripetal force.

Testing 

1. Rotor

To test the the rotor connect the mulitimeter (in the ohm setting) to the rotor shaft and the bottom slip ring. this test will check for a short circuit. the reading should be infinity

To see if the rotor is still in good working condition connect the multimeter to the two slip rings. Check that the ohm reading is the same as specified

     2.  Stator

Check that all the copper coils have an ohm reading that complies with the specifications. If there is no reading it means that a coil has become disconnected

    3. Rectifiers

Use the Diode testing setting on the multimeter. Connect the positive wire to the B+ terminal and the negative wire to the negative side of the diodes. Then connect the negative wire to the body of the alternator and the positive wire to the positive side of the other diodes. If there is no reading it means the diode is broken.  

   4. Brushes

Measure the brushes with a vernier caliper. If the the measurements are less the 4.0mm then the brushes need to be replaced

Health and safety puzzle

Testing an alternator

How to check if the alternator give off a charge


Connect a voltmeter in parallel between the negative terminal of the battery or on the body(ground) and the (B+) wire on the alternator this should give a reading of the voltage that is produced

What checks to do before testing

• visually inspect the wiring for any loose connections or corrosion
• check the tension of the belt that drives the alternator and its condition (should not have cracks)
• check to see that the charging light comes on when the car is switched on
• check the alternator bracket 
• visually inspect the alternator its self for any obvious damage or if any oil has leaked on to it

Testing the voltage drop

Before testing start the engine

To test the voltage drop connect the multimeter with the com wire to the negative terminal of the battery and the positive wire to the body of the alternator. To check the positive voltage drop connect the com wire to positeve terminal on the battery and the positive wire to the B+ terminal.