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Diagnose a faulty Ignition System

Diagnose a faulty Ignition System

Ignition system consists of a number of components like spark plugs, ignition coils, etc. It’s responsible for the starting of a car. However, in case of an unlikely event of ignition failure, you might not be able to start your car. In such a scenario, it is important to know how to diagnose your car’s faulty ignition system.

The ignition coil must be able to produce a large enough potential difference (voltage) at a rate that can increase the reliability and efficiency of the engine’s operation. This can be achieved by using an advanced material and design that will allow for a coil to survive several thousand volts of energy. Some coils are made to be maintenance free, however most wear out over the vehicle’s life cycle and require replacement.

Types of Ignition Coil

There are a few different types of coils, each with their own advantages and disadvantages. Coils come in two types depending on whether or not they employ a heavy magnet core.

  • The first type of coil, induction coils, use a heavy magnet to create an extremely strong field that will induce a current in a wire coil.
  • The second type of coil, transformers, use a core of inductive material such as iron that acts as a secondary winding for the inductive coil. 

In vehicles with coil-based ignition, coils are generally controlled by a master computer that is able to monitor and distribute the energy throughout the entire coil system. When a diagnostics check is required, it is possible to test individual coils or the entire system. 

When examining a single coil, it is important to note the polarity of each lead, as well as the condition of the coil itself. Although all ignition coils are polarized, the leads can be differentially marked (positive and negative, or common and cathode), or marked at all (OEM coils). It is also important to note whether or not the coil has external connections. If the coil does have connections, it is important to note their condition (busy, shorted, open). In addition, the connections should be checked for continuity. 

Coil groups can be tested by setting a multitester on each lead of the group, and starting the vehicle. The testers should provide a sweeping ting-a-ling on each lead, as well as assess the group by putting it in the on position and noting any ignitions.

How to Test Individual Ignition Components

In addition to coils, it is also possible to test individual ignition components. Spark plugs have leads that must be connected (or chafed to be able to make a spark), as do distributor caps. Ignition switches should also be tested, as should the crankshaft position sensor and any position-sensitive components (throttle body, exhaust valves, water pump).

The ignition system can be tested by having a multimeter in the on position. If an individual component is tested, the tester should be set to the continuity setting and moved quickly back and forth. If a group is tested, a sweeping ting-a-ling test should be used.

Identifying which Ignition Component is failing

Once the system is tested, it’s time to fire up the vehicle. Hopefully, there will be an ignition at some point.

  • If no ignition is heard, there may be some sort of electrical short (this is most common with the negative battery cable being pulled loose or forgotten)
  • If only a clicking sound can be heard, the coil may be shorted.
  • If a sound of two distinct claps is heard, the distributor cap may be at fault.
  • If the engine fires up but then quickly dies down, the ignition timing is probably too advanced.

The engine may also die when cold. In this case, the glow plugs may need to be heated up before driving.

In the rare instance that there is no confirmation of an ignition, it may be necessary to try other methods of starting the engine. This may involve trying the key a few more times, taking off the fuel tank cap and letting the fuel sit for a few minutes, or just pushing the starter button a few times. If all else fails, it may be necessary to tow the vehicle to a local mechanic.

The Final Test – Drive

Once the vehicle is started, it’s time to drive it. Driving should confirm if the ignition is functioning. In addition to driving, pay attention to fuel consumption. If the vehicle uses gasoline, there should be a fuel gauge somewhere. If it’s working, fuel economy should be fairly accurate. In the event that the fuel gauge fails, pay attention to the odometer. When the vehicle reaches five miles past where it should be, pull over and let the engine coast to a stop. Any further driving should be done using electric power alone.

If the vehicle is diesel powered, or if the electricity supply is not reliable (i.e. off during a storm), pay attention to the speedometer. The engine should remain idle at a specific RPM. If the engine is revving faster than expected, a mechanical failure may be occurring. If the engine is revving slower than expected, a problem with the fuel supply may be occurring (if using gasoline). In this case, the vehicle should coast until reaching a safe stopping place.

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