car tune up process

Detailed Tuneup Procedures

Previous articles have covered the most common tuneup procedures, and some more advanced. However, there are several car components mechanics tend to overlook during a tuneup. In this article, we will go over some detailed tuneup procedures.

engine checkup

What Is an O2 Sensor?

The job of O2 or oxygen sensors is to measure the oxygen content in the engine exhaust and compare it to oxygen content in ambient air. On one side of the O2 sensor, there are small holes where the air from the atmosphere comes in and the sensing element on the other side. This difference in the amount of oxygen molecules produces a voltage, depending on the engine running conditions. If the difference between the oxygen molecules inside and outside the exhaust is high, the voltage will be high, as well.

Car ECU uses this value to determine if the engine is running rich or lean. Rich running condition mean that there is too much fuel and will result in high voltage. On the other hand, a lower voltage means there is not enough fuel. We call this a lean running condition. The ECU continuously adjusts the air-fuel mixture based on the data from the O2 sensors. This is why checking O2 sensor is important for tuneup. 

o2 sensor comparison

Where Are O2 Sensors Located?

The number and location of oxygen sensors varies depending on the make any model of the car. A car with a four-cylinder engine will most likely have two sensors. The first one will be a pre-cat or upstream sensor. It comes before your catalytic converter and determines if the engine is running rich or lean. The voltage it gives will oscillate from 0.1 to 0.9 volts if the engine is running as it should. The second one is a post-cat or downstream O2 sensor, and it monitors the efficiency of your catalytic converter. If everything is OK, it should give readings around 0.5 volts. Bigger V6 or V8 engines will have separate sensors for each bank. In the end, some sensors have a small heater that helps the sensing element to achieve operating temperature faster.

What Happens If The O2 Sensor Is Bad?

As the oxygen sensor is exposed to exhaust gases, it can get dirty and clogged with time. This will cause many running issues, ranging from stalling and bogging under acceleration to black smoke from exhaust and poor gas mileage. In most cases, a faulty sensor will trigger a ‘check engine’ light. Scanning for fault codes is the best option, as it will pinpoint the fault. It is also possible to check the sensor with a multimeter. With it, you can measure the heater resistance and sensing element voltage. If the values are outside recommended ranges, replace the sensor.  

How to Change Your Vehicle’s Fuel Filter?

Another important step during tuneup is fuel filter replacement. To avoid damage to the engine components and develop full power, modern engines need clean fuel. The only way to achieve this is to use high quality filters, as dirt particles and water can enter the fuel in various ways. These impurities lead to wear and corrosion of the sensitive injection systems and other engine components.

car fuel filter

Another fuel filter function is water separation. This is extremely important for cars with diesel engines, as even the smallest amounts of water will cause damage to the very sensitive injection system. In addition, diesel fuel filters must remain fully operational during harsh winter conditions. If the outside temperature is low enough, paraffin crystals form in diesel fuel and can clog up the filter. To prevent this, diesel fuel filters return heated fuel to the filter, ensuring that the fuel in the tank is not too cold.

Fuel filters get dirty over time, which obstructs fuel flow. Symptoms of a bad fuel filter are hard starting and engine stalling under hard acceleration. Also, a dirty fuel filter has a high flow resistance, which puts additional strain on the fuel pump and can cause vehicle breakdown. Lastly, the filter medium can tear, allowing unfiltered fuel into the injection system. This will cause scoring of the injection nozzle and engine wear, resulting in reduced engine output. Changing the fuel filter is a fairly simple task. In most cases, they are located under the car near the fuel tank. However, some engines have fuel filters on the side of the engine.

When Should You Change A Distributor Cap and Rotor?

An ignition system is a complex electrical system whose function is to produce a spark and initiate the combustion process. The main parts of a typical battery ignition system are battery, ignition switch, ignition coil, contact breaker with a condenser, distributor cap with a rotor, and spark plugs. The battery provides a low voltage electrical energy. It connects to an ignition coil, whose function is to create a high voltage current required for inducing an electric spark. This is done with the help of a contact breaker, which has a condenser.

A distributor, as the name would suggest, delivers the high-tension voltage to spark plugs in the correct sequence and at the correct time. It consists of a rotor in the middle and metallic electrodes on the distributor cap. These metallic electrodes connect directly to the spark plugs and are also known as ignition harness. The secondary winding of the ignition coil connects to the rotor within the distributor. The camshaft connects to the rotor, and drives it. As the rotor rotates, it passes the high-tension current to the ignition harness, which then carries the currents to the spark plugs.

distributor cap

Over time, the rotor arm tip and metallic electrodes on the distributor cap will wear out. If the gap between these two components is too wide, it will stop the high-tension current. The first signs of a bad distributor cap and rotor are a random misfires. As a result, the car will shake and sputter during acceleration. Various outside contaminants within the distributor, such as water or dirt, can also cause similar problems. Replacing the cap and rotor during tuneup is the best solution. They are not expensive and, in most cases, easy to replace. Some manufacturers even have recommended intervals for replacement. This prevents issues even before they occur.

About Bojan P

My name is Bojan - I am a car enthusiast, specialised in the vehicle diagnosis, repair and maintenance with 10 years of practical, hands-on experience. In addition, I have a Masters degree in mechanical engineering.

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