Automobile Maintenance: Engine Tune-Up - Air Filter, Spark Plugs, Crank Sensor, Idle Air Valve

Note :  This post is not about "tuning", it is about tune-up.  The two should not be confused.

Here I discuss four elements of engine tune-up namely air filter, spark plugs, crank sensor and idle air valve. Of course there are other things like ignition wires that need to be checked or replaced but that would be covered in other posts. 

If you have to replace your air filter, why not replace it with a filter with low-resistance to air flow? Some filters enclose their paper filtering element with perforated metal sheets, which is not ideal for free air flow. A wire gauze air filter is shown below. It offers less resistance to the air flow than a filter with a perforated metal sheet.

If you are installing new spark plugs, measure and adjust the electrode gap of all spark plugs before installation in your engine using a thickness gauge. Each petrol engine has its own electrode gap specification.

If you are not replacing the spark plugs, you can just clean them with a fine spark plug file. Only clean the side electrode in shape of L and not the central electrode. Remove the burnt metal to expose new shiny material on the protruding electrode (image shown below). Use the spark plug socket of required size for removal and re-installation of the spark plugs taking care not to tighten the plugs too much otherwise the threads may be damaged. Ideally use a 3/8 inch ratchet for plugs.

Indexing the spark plugs is good for better combustion through better exposure of the spark to the air-fuel mixture. For indexing, mark the plug with a line corresponding to the open gap of the electrode. What is desired is that this open gap should face the air fuel mixture. When installing the plug in the cylinder head, this line would give you an idea as to the position of the open gap. Indexing will only be verified after the spark plug has been tightened. Different spark plugs would stop at different positions so you would need to try different plugs.

Here is a view of the combustion chamber of a 2-valve per cylinder petrol engine. It is number 2 cylinder as is shown by markings on the valves.  The spark plug's open gap is facing the center of the combustion chamber, hence it is indexed. Indexing is not really needed if the spark plug is situated in the center of the combustion chamber (found in 4-valves per cylinder engines).



In the image below (number 4 cylinder), the open gap of the spark plug is not facing the center of the combustion chamber and hence it is not indexed.

You can also optionally side-gap your spark plugs for increased torque as used by racing spark plugs. Side-gapping changes the path of the spark from straight to inclined, which is supposed to increase exposure of spark to the air fuel mixture. The image below shows a normal plug on the right and a side-gapped plug on the left.

If you are doing engine tune-up, why not check and clean the crank sensor? Crank sensor (shown below) looks for a dent on the flywheel and is used to control ignition advance and fuel injection. It is an electromagnetic sensor and should be cleaned for better signal reception. The resistance of the crank sensor should be checked with a multimeter (and compared to specs) to confirm its health. If you can adopt a non-metallic shroud for the wire of the crank sensor, it would protect it from any possible electromagnetic interference.

Next comes the idle air valve or idle air control valve (IACV). It regulates  the air flow while starting the engine or during deceleration. It is controlled by ECU or computer and if this valve does not close when it is commanded to close by the computer, it can cause an air leak and thus increased fuel consumption. Therefore, it should also be maintained. Mark the air entry and exit so as not to confuse them when remounting.

Lubricate and clean the valve with a brake cleaner or carb cleaner or whatever you have that shall remove deposits. Check the electrical contacts and measure the resistance of coils with a multimeter to establish the good health of the valve.

For a complete job, you would need to open the valve and check the "Rolling electrical contacts (if any)" which may become loose over time, affecting the performance of the valve.