Fuels day one

FUELS

Fuel is the energy source for any engine.  It is fed into the combustion chambers through a system built of fuel pumps and injectors.  It is very important in any car to have a healthy fuelling system for the best efficiency and performance.  any upgrades in horsepower in cars must be followed up by the consideration of upgrading the fuelling system to feed more horses.

even though 80% of the energy in fuel is lost through heat, it is the most efficient way to run engines today (aside from hybrid technology).

The system is a very simple construction.  In the basic naturally aspirated engine,  it will include a fuel tank, followed by a fuel pump, a fuel filter, a fuel line and regulator, and a hose that directs excess fuel back into the tank.  A high pressure hose connects the parts together, and is braided for fire safety reasons.  The fuel line runs along the cylinders and is bolted onto the intake manifold and the injectors are slotted into holes inside the manifold.

Inside the injectors are small solenoids which open and close a small nail shaped piece that sits inside a tap.  As the solenoid gets power, it pulls the nail shaped piece inside and opens a path for the pressurized fuel to pass through and eventually into the combustion chamber.  These injectors can be tested by using a small LED tester to test that a power output is being supplied at a healthy rate.  It simply works by unplugging the injector terminal and plugging the LED light into the cable.   The light should flash, and speed up as revs increase.  To check that the solenoid is moving freely,  a stethoscope or a screwdriver can be placed on the metal body of the injector and a sharp clicking sound should be heard when put to the ear.  The sound should click at a similar rate between all injectors. An ohm meter can also be used to check the injectors.  To do this, simply unplug the cables from the injectors and place the meter points on each pin of the plug.  Compare readings with the car's specifications.  If you cannot get a hold of this, the best thing to do is to compare each injector with each other.  They should all give similar readings.

The fuel rail should have a type of regulator on the end, it's a small instrument that contains a valve to open and close a pathway for the fuel in the fuel rail.  It is controlled through a hose that connects the valve end to the manifold.  It uses the vacuum pressure of the manifold to open and close the pathway for the fuel.  When the engine is under load, vacuum pressures drop,  which lets the regulator close.  When the regulators closes, this causes the fuel rail to increase in fuel pressure, meaning, when the injector opens,  more fuel pressure passes through meaning more fuel is injected.  The injectors also open at a longer duration at each opening but that is controlled via ECU. When the throttle body closes, the manifold creates a very strong vacuum pressure, built up by the cylinders sucking air.   The manifold has very small opening for air to pass into when the throttle is closed, this causes it to create a vacuum pressure.  This vacuum pressure passes through the hose to the regulator, opening the valve and letting fuel pass through. The throttle is generally closed when the accelerator is not operated. In a forced inducted car,  the regulator is a sophisticated electronic device that controls the fuel pressure.

Injectors must be maintained cleanliness,  a dirty or failing injector will not spray in an efficient pattern otherwise will not spray consistently.   They are usually blocked up in the filter inside from deposits and carbon build up.  They can be cleaned by three different methods;  using an injector cleaner agent which is poured into the fuel tank,  using EFI cleaning liquid from a pressurised can, or they can be removed and processed through an injector cleaning machine.

Our tests:

We tested a Toyota 4A-FE engine mounted on a display.  This means that we could not put a load on engine itself.  However, we did test the differences when the regulator was plugged and unplugged from the intake manifold.  The display had a hose running from the intake manifold into a gauge,  which displayed the vacuum pressure level.   As the throttle opened, the vacuum pressure inside the manifold dropped to around 8Psi from its idling 11Psi.  The display also had a gauge to show the fuel pressure. The fuel pressure spiked up to around 50psi when the regulator shut closed (high rev) and dropped to around 40Psi when idling.  Vacuum pressures would change if engine overall was under load, ie vehicle is moving up hill or carrying heavy loads.

A screw driver was placed on the fuel injector itself and placed near the ear.  We heard a chipping ticking sound from the injector's solenoids operating.  Ohm meters were used to test the resistance of the injectors.  all four showed an average reading of 14.7.  All injectors being unplugged individually caused the idling rev to drop by 200RPM.  LED lights were used to test the cables and they were sending a consistent pulse.  All readings were recorded into our booklets for future reference.

Hans later on explained how various sensors including O2 sensors, MAF sensors, air temperature sensors and the TPS (throttle position sensor) are used to send signals to the ECU to control the injectors behaviour. 

I'm glad that this topic is currently based on electronic fuel injection because I hate carburettors.