Oxygen Sensor Tester

The Oxygen sensor measures the amount of oxygen in the exhaust gasses and it sends signals to the ECU so that it can monitor if the engine is running rich, lean or at stoicheometry. When the tester is connected to the oxy sensor it displays what the air fuel mixture ratio is that the engine is running on. It will display a red light if it is running rich, a yellow light if it is stoich and a green light if it is running lean. The oxy sensor is back probed and connected to the oxy sensor tester. The tester measure the voltage and it displays whit the fuel mixture is.

Exhaust Gas Analyser

The exhaust gas analyser is used to measure the amount of emissions a car is producing. It can also detect what the engines air/fuel ratio is whether it is running lean, rich or at stoicheometry (14.7 : 1). The emissions that cars produce are harmful to the environment so governments started putting laws up on how much emissions a car is allowed to emit. The exhaust gas analyser can also be used to diagnose problems on the engine.

 An example of exhaust gas measurements

Problems related to higher than normal readings:

• High HC (hydrocarbons) - May be due to a misfire
• High CO (carbon monoxide) - Could be from the engine running to rich
• High O2 (oxygen) - Means the engine is running lean, there is a misfire or there is a hole in the exhaust
• CO2 (carbon dioxide) is an indicator of how efficiently the engine is running

It is important to allow the exhaust analyser to measure the residue in the pipes and allow it to re-calibrate before inserting it in the exhaust pipe. It is also important to have a ventilation pipe securely fitted to the exhaust to prevent inhaling poisonous exhaust gasses. The analyser should be set to catalytic converter if the vehicle has one, if it is not set up properly incorrect measurements may be recorded.

Automatic Transmission

An automatic gearbox has complex gear sets in them. The gear sets consist of sun, planet and ring gears. The gear ratios are controlled by the bands braking the ring gear forcing the planet gears to drive the output shaft or it releases the ring gear and allows it to drive the output shaft. The bands are controlled by pressurised hydraulic fluid that is pump through the gearbox. The same fluid is also used to lubricate the moving parts in the gearbox like the bearings. Older gear boxes would control the gear selection using mechanical shift valves  linked to the kick down switch that is connected to the trottle and the governor. Newer cars use mostly clutch packs instead of the the bands and the fluid is directed to them using solenoids that are controlled by the ECU according the the engine speed, the speed of the vehicle and the load on the engine (the amount of vacuum in the intake manifold.

We took an old rear wheel drive automatic gear box apart, it had two bands that would lock the ring gears according to which gear is selected. The bands were controlled by an actuator piston that would push the two ends of the bands together locking down on the ring gear. The governor was located on the output shaft and the oil pump was located on the input shaft. The oil pump in the gearbox is a crescent type pump.

Before removing and stripping down the gearbox it is good practice to take out the dip stick to check the colour and smell of the transmission fluid. The colour and smell can help a lot with finding the problem. If the fluid smells burnt it means that the clutch pack or the bands are slipping causing them to burn. If the fluid is milky it means it has been contaminated by water. If the engine flares between gear changes it means that the transmission oil is low or the clutch pack is worn down or the bands need to be adjusted, it could also be because the oil pump is worn out and it is not supplying the correct amount of pressure or there is a blockage in the fluid passages.

 Bottom of the gearbox with its sump off

 Park locking mechanism

 Outside of the oil pump

 Governor, the governor controls the oil pressure using centrifugal forces

Axle, gears and the oil pump

This is a diagram to show how the oil pump works

The inside of the oil pump from our gearbox looked like the one in the picture above

Differential

The differential is used to change the direction of the engine's rotational motion. The diff uses a pinion and ring gear to drive the wheels. It uses spider gears to control the speed of each wheel around a corner. The differential also reduces the speed and it increases the torque supplied by the engine because of the gear ratio between the pinion and ring gears.

On the differential that we disassembled we found that the pinion gear was damaged and that the pinion gear shaft had a roughness to it when we turned it which may be caused by faulty bearings. Another problem we found what all the bearings and the spider gears were worn. The wear on the differential parts may be caused by a lack of fluid or prolong usage of the diff (high KMs). The spider gears were also cracked and chipped.

Differentials do not have a lot of moving parts but it is important that there is the correct amount of clearance between the gears to reduce the backlash. It is also important to use the right oil (SAE 75) and to make sure that the oil level is at the correct level.

Drive shafts

The drive shaft connects the gearbox to the wheels of the vehicle. Cars have suspension to absorb the the shock from the road to create a smother ride for the driver this means that the wheels move up and down according to the road. The drive shaft connecting to the wheels need to be able to move up and down while supplying the driving force, the constant velocity, universal and tripod joints make it possible for the drive shaft to move with the motion of the wheels while rotating them.

Constant velocity and tripod joints


The cv/tripod joint configuration allows the drive shaft to rotate at greater angles (45-52 degrees) than universal joints and it has less friction than the universal joints. The CV and Tripod joints have boots that cover them if the boots get worn and it tears then the joints may get contaminated by dust and water resulting in the CV/Tripod joints to wear out faster.

To service the CV joint we removed it from the shaft and dismantled everything. Then we cleaned it and  checked for signs of wear.

CV Joint

Tripod Joint

Universal joints


Universal joints are generally used in rear wheel drive and heavy vehicles. They cannot work at large angles like the CV joints but they are able to withstand larger rotational forces.

When servicing the universal joints we removed the snap rings and pressed out the spider/cross. When fitting the new cross make sure that needle bearings are in place before pressing it in.

Manual Transmission

A gearbox is used to convert the torque and speed from the engine to the wheels using gears of different sizes. A car needs to have high toque and low speed when it is pulling off other wise the engine will stall so gears go from small to big. At high speed the gearbox has gears that go from big to small to increase fuel economy and vehicle speed. The higher gears produce more speed and less torque. The gearbox also allows the vehicle to revers by adding another gear and changing the direction of the output drive.

A trans-axle gearbox has two shafts inside of it, the one that comes from the engine and another that is driven by the gears going to the wheels. The gears are engaged by a selector pushing the dog gear into the driving gear. Before the gear is engaged the synchromesh slows the driven shaft down to the same speed as the gear so that the gears can engage with out clashing. Once a gear has been engaged the wheels turn at the speed that its determined by the gear ratio of the driving gear and the driven gear.

It is important to use the right lubrication for a gearbox. If the wrong lubrication is used like differential oil it can cause the synchros to slip and that would result in the gears crunching it could also produce more wear on the gears.

Diesel engines

Glow Plugs


Glow plugs are used when the engine is cold, it heats up the air in the cylinder so that the engine starts easier. The time that the glow plugs are on is controlled by the ECU. The time is calculated using the temperature measured  by the temperature sensor.

To check the glow plugs first see if they receive the correct voltage using a multimeter, then check the amps by connecting the multimeter (set to amps and make sure it can handle the amount of amps) in series to the glow plug circuit. If the reading on the ammeter is less than the specifications check each glow plug with a ohmeter to see if it is working. If the glow plugs are faulty they can be removed and tested on the bench with another battery. The glow plugs should heat up in 10 to 15 seconds and it should not start from the tip.

The difference between petrol and diesel engines


The fuel in a petrol engine is ignited by an electrical spark, in a diesel the fuel is ignited by heat created by compressed air. The speed of a diesel engine is controlled by the amount of fuel that is added and a petrol engine is controlled by the amount of air added. Diesels are more fuel efficient and have more power at lower engine speeds


Checks for a non start diesel engine


*Check that there is fuel in the system and that there is no air trapped in lines. The injectors can be loosened to check for fuel. The condition of the fuel should also be checked
*Make sure that the battery is able to crank the engine
*Check the compression on all the cylinders
*Check the glow plugs, the engine will have trouble starting when it is cold without glow plugs

Bleeding a diesel engine


To get the air out of the system loosen all the injectors then crank the engine until fuel starts coming out the side of the injectors the tighten them up again. If not all the air is out then do it again.

The diesel bug


When the fuel tank stands for a long time the fuel evaporates and condenses at the top of the fuel tank then the water mixes with the fuel that creates an environment for bacteria to grow the bacteria that grows in the fuel is known as the diesel bug. The "bug" can clog the fuel pump and injectors. To prevent getting a diesel bug its best to keep the fuel tank as full as possible, drain water from the system regularly and get fuel from suppliers that maintain their fuel well.

The diesel injector 


The mechanical operated injectors have spring loaded valves in them that are forced open when the fuel from the pump reaches a certain pressure therefor spraying the fuel at a high pressure into the cylinder. The electronic injectors on common rail diesel engines are controlled by the ECU it receives high pressured fuel from the common rail that is presurised by the fuel pump. Another type of fuel injector is the pump injector it receives fuel at low pressure and pressurizes it by the camshaft lobes pushing down at the top of the injector the pressure is then released by the ECU sending the injector a signal which then opens it via a solenoid.

Injector pump


The injector pump, pumps the fuel at high pressure to the injectors. The two commonly fitted pumps are in line and distributor pumps. A distributor pump is similar to the distributor in a petrol engine it supplies the fuel to each cylinder according to the timing.

Diesel pump timing


We set the timing for a Mazda diesel engine. First we loosened the bolt (in the middle of the four high pressure lines that go to the injectors) on the diesel pump and put the DTI gauge in its place. Then we turned the crankshaft to 30 degrees before T.D.C and zeroed the Gauge. Then we turned the crankshaft to 2 degrees after T.D.C. We then loosened the diesel pump so that it was able to pivot, moved it so that the reading on the Gauge matched up with specifications and then tightened the diesel pump again. We removed the DTI gauge and replaced the bolt. The flywheel has marks on it in degrees


Petrol and diesel pistons


Diesel engines generally have pistons with flat heads with concave areas in. This design creates a higher compression and the concave areas create an air flow which causes the fuel to burn better.


Turbo


A turbo is bolted to the exhaust pipe and has a turbine that is powered by the exhaust gasses. The turbine is connected directly to the a compressor that forces air into the engines intake.




Servicing a diesel


When replacing a diesel filter fill the new filter with diesel to reduce the amount of air in the system. Before starting it the system should be bled to get all the air out.

Off car fuel injection testing

The fuel injectors are usually mounted on the intake manifold but some engines have the injections injecting directly into the cylinders. The injectors along with the ECU, fuel pump and fuel regulator controls the amount of fuel that is injected into the cylinders. In an injector there is a needle that is controlled by a solenoid, when the solenoid receives power it pulls the needle back allowing fuel to go into the cylinders and if the power is off the needle moves forward again blocking the fuel entering the cylinders. The injectors are opened and closed by the ECU sending it power accordingly to the engine timing.

Experiment


We did a off car injector test using an injector tester. We connected the four injectors in the tester and switched on the machine. We did a flow test to check that the injectors have the correct spray pattern. Then we did a normal function test to see if the injectors opened and closed correctly and if they functioned at higher RPMs. The last test we did was the hold test to see if the injectors would leak if they were closed.

Reflection


The injectors are cleaned in a ultra sonic bath to loosen any carbon or debris in the injectors then it is washed out by back washing it. If a injector has a irregular spray pattern it needs to be clean or replaced because if it does not spray correctly some of the atomized fuel will condense in the intake manifold instead of going into the cylinder which means there is less fuel in the cylinders to burn and that causes the engine to run lean. If a injector leaks when it is off the pressure in the fuel rail will drop, this means that the injector that is opened will have less fuel passing through it cause the engine to run leaner. The fuel that leaks into the intake manifold will condenses on the sides and will not burn properly when the intake valve is opened this creates more pollution due to the higher amount of unburnt fuel (HC) coming out of the exhaust and it reduces the fuel economy. It also drains the fuel in the fuel rail when the car is off causing the car to take longer to start and it wastes fuel.