No-Start Diagnostics

All vehicles need 5 things in order to start and run properly:

• Fuel
• Air
• Spark
• Compression
• Coordination

Some Background Information

Before we get started, here's some information about what those five things are and why they're important.

Fuel

Fuel, gasoline, petrol, whatever you may call it, is a hydrocarbon based liquid that ignites under specific conditions (typically compressed, in vapour form, and exposed to electrical arc or open flame).

Fuel is typically delivered to the engine from the tank through fuel lines, pressurized by a fuel pump. Our fuel pump is located in our gas tank hanging from a fuel sending unit.

Once the fuel arrives at the engine, it is delivered to the fuel rail where it is kept pressurized until injected into a cylinder's combusion chamber by a fuel injector.

Fuel is typically also filtered before it arrives at the engine in case any impurities have made their way into the tank such as dust or rust particles. We have two fuel filters in our cars, one is a "sock" over the inlet of the fuel pump, and the other is an inline fuel filter situated in the engine bay.

In its liquid form, gasoline is actually pretty stable, and wont explode as it often does in video games and movies. It must be vapourized in the correct ratio of air to fuel in order for it to combust.

Air

As previously mentioned, fuel needs to be mixed with air in order to combust.

Air is brought into our engines through the (starting at the engine) intake manifold, plenum, throttle body, intake pipes and mass airflow sensor. Turbocharged models have their intake air compressed by a turbocharger in order to achieve higher air density. The additional air requires more fuel in order to maintain the proper ratio, which when added will result in a more powerful explosion and therefore more power.

Too much air in the system is referred to as "running lean" (not enough fuel for the amount of air), while not enough air is referred to as "running rich" (too much fuel for the amount of air). A bad air to fuel ratio can produce inconsistent combustion, sometimes resulting in unspent fuel being sent out the exhaust or up the intake.

Compression

The air and fuel mixture has to be comressed in order to combust properly. Combustion is achieved by locking the air to fuel mixture in a combustion chamber in the engine (cylinder) which is then squished by a piston propelled by another cylinder's power.

In order to maintain high compression, the valves that allow air into the cylinder must seat tightly against their seals, and the rings which seal the piston to the cylinder wall must be intact.

Spark

The mixture of air and fuel has to be ignited once compressed. Ignition is achieved by feeding an electrical current into a spark plug, which jumps the gap between the tip and the core of the plug. This spark is enough to ignite the compressed air and fuel mixture (if it is at the correct air to fuel ratio).

If the spark isn't strong enough, or doesn't happen at all, the fuel isn't ignited, and the unspent fuel can exit the cylinder via the intake or exhaust valves.

Coordination

Finally, as you may have been able to tell from the previous information, all of these things have to happen at the right time. This is maintained mechanically by the timing belt, and electronically by the engine control unit (ECU).

Diagnosing What's Missing

In order to diagnose why one of these items is missing, we first have to determine which one is absent.

Determining if Fuel is Present - Fuel Pump, Fuel Filter & Fuel Injectors

This section will, in the future, describe how to check if you are getting fuel at the fuel rail.

If you have determined that you are missing fuel, please visit our missing fuel sub-page for further directions.

Determining if Air is Present - Air Filter, Mass Airflow Sensor & Intake Piping

This section will, in the future, describe how to check if you are getting air to your intake plenum.

Determining if Compression is Present - Cylinder Valves, Head Gasket & Piston Rings

This section will, in the future, describe how to check if you are getting compression in your cylinders.

Determining if Spark is Present - Spark Plugs, Ignition Coils & Power Transistor Unit

This section will, in the future, describe how to check if your spark plugs are firing.

Determining if Coordination is Present - Engine Control Unit, Spark Plug Firing Order & Valve Timing

This section will, in the future, describe how to check if all four of the previous items are occuring at the correct times.