WS1 & WS4 Fuel injectors testing and fuel flow

WS4 Fuel Pressure and flow.

You start your car up in the morning, it only cranks. You check the battery, then pretty sure it is not the power side because it can crank pretty well. What is the next thing: Fuel.

Normal construction of a fuel line is: Fuel Tank, Internal pump, External pump, Fuel Filter, Fuel Rail, and finally the injectors or a carburetor.  Fastest way to make sure there is fuel in the line is try losing the fuel pipe from fuel filter to the rail, or the return line – given that ignition is ON. Fuel will pretty much spray into your face, not really dangerous but just don’t let it get into your eyes.

You get the idea, the purpose of this assessment is giving us an idea of what supposes to happen in the fuel line. One property that virtually decides whether there is enough fuel in the line or not is PRESSURE. If we have enough pressure, I mean High pressure that can spray line water pump, that means we have enough fuel flow, both volume and speed.

The model this time is Toyota 4A-FE 1999, with fuel line pressure on spec is approx. 260-300Kpa (2.7-3.1Kgf/cm²; 38-44psi). With the key on, engine off, we still get 260kpa/37.5psi (actual), this is not maximum but just enough to start the engine. Maintaining pressure means there must be no leak, if there is a loss of pressure, check for leaks first, because it is very obvious.

Increasing engine load not only demands more fuel, injectors must also spray faster. Because combustion time is approx. equal for the same amount of mixture, combustions at higher speeds means less efficient combustions. So it is ideal to make fuel more pressurized, atomized, so it is easier for combustion to take place, even reduce combustion time. The fuel pump can hence pump stronger using more battery power to meet the demand. There are many specifications for each engine load level, but for this one, there is a maximum pressure it can provide which must be above all engine loads. This pressure can be achieved by simply clamping the return line, gauge will jump above 600kpa.

Idling: 280kpa

WOT: 340kpa

Residual, this should be equal to the Key on pressure: 260kpa, it is ideal for the next start.

Sometime, the fuel tank can be contaminated with other gas or liquid, especially water. Or even more badly, there is a clog somewhere on the fuel line that the pressure gauge reads excessively high, or nothing at all because fuel can’t reach there. Well, better check the fuel flow with your own eyes, and best is to check the return line, because if there is fuel to return, then there is more than enough to burn. It is just that the return flow is NOT the main line flow, so it is pretty low 0.5liter/s. If your main line is like this, you’d better check your pump for weakness or your filter for blocking the flow.

Your car will likely to have these symptoms when there is something wrong with the fuel line:

Low pressure: Less atomized fuel, less efficient combustion, more un-burnt fuel, flooding, will cause very rough idle and low power when reving.

Low flow: leaner mixture, hard cold starting, more emission and heat spots, lead to detonation and pre-ignition. Mixture takes longer to burn, harder to ignite, loss of power when reving.

Excess pressure: Richer mixture, more unburnt fuel, hurt fuel economy, more CO and HC emission, HC is bad for CAT converter and damage for the fuel lines.

Faulty pressure regulator: Loss of pressure, or excess pressure, leak; intermittent engine operations and damage for the fuel line

WS1 Petrol Fuel Injector Testing:

Injector is a very small, intricate and precise actuator. We can only know if its plunger is open or close by a sound of a click or its switching voltage characteristic.

Injectors use battery voltage for their solenoids to switch the plunger open and close. So with ignition on, engine off, we can check for battery voltage on the injector plug. When the engine is running, we can also use this voltage to hook up an LED tester, available voltage will light the LED. The thing is injector is switched rapidly according to engine speed and acceleration, so we should see a rapid flashing LED instead of a still LED.

Injector, like any other actuator has its own cycle: (picture)

This enables us to check its frequency, duty cycle, because a graph is prevail.

With the duty cycle testing on a Multimeter, we can see how long it opens in 1 cycle in proportion to the whole time of 1 cycle. For example: At idle, we know the switching is less frequent (7-12Hz) and also narrow pulse width, so we get around 4.5%, as we rev the engine up, we know the switching is more frequent(20-25Hz) , plus the pulse width will be longer: ~13-18%. But this only happens when there is demand for acceleration, not stable RPM, because it doesn’t need that much fuel to keep the engine @ the same speed.

Combining duty cycle and Frequency in a formula we can get the pulse width of an injector at that time:

Pulse width(ms)= (Duty cycle/100)/frequency, that is 4.6/100/7 * 1000(in millisecond)=6.57ms