The modern-day fuel delivery systems use adaptive fuel pressure control to boost fuel efficiency. By only allowing the fuel required, the wastage of fuel is greatly reduced.
But to get such control, the high-pressure fuel pump uses something called the Fuel Metering Valve.
What is a fuel metering valve?
As the name sounds, the fuel metering valve is a fuel control unit that controls the amount of fuel fed in the injection pump later to the cylinders. The Fuel metering valve is controlled by an ECU controlling the fuel-fed based on the engine’s requirements and the current fuel pressure.
Without a metering valve, the amount of fuel won’t be controlled resulting in unbalanced power production.
For a metering valve to work, it needs the fuel pressure sensor to send accurate pressure reading to the PCM (Power-train Control Module) or the ECM (Engine control module).
Based on the reading, the PCM/ECM calculates and sends the fuel required to the Injection pump by using the metering Valve. The metering valve is controlled or adjusted via PWM (Pulse Width Modulated signal), controlling the fuel input ensuring that the engine is only fed the amount of fuel required.
Hence reducing fuel wastage and increasing efficiency.
How does a fuel metering unit work?
The fuel metering unit works on a very simple spring-based plunger design. The idea is to pass a given amount of fuel based on the fuel pressure reading. To do so, the ECU receives the signal based on requirement and creates an opening. Since the plunger is spring-loaded, it initially opens completely due to spring action.
But to control the fuel amount, the opening must be controlled as well. To control the opening, a solenoid is used which creates a magnetic field to control the opening against spring action by attracting the plunger. (Use the image above as a reference).
The Metering valve solenoid is powered by connecting to a system relay’s positive side while the negative side is switched to the ground by the ECU. It is the duty cycle( ratio of on and off time ) of the solenoid that decides the plunger’s position. A longer duty cycle means high fuel pressure while shorter means low fuel pressure.
Types of Fuel Metering Valve:
There are generally two types of fuel metering valves designed based on their applications. You have the Straight Head Fuel Metering Valve. This type of valve is used in industrial machines and big trucks with 6-cylinder engines. While the other, the Bent Head Fuel Metering Valve is used in normal 4-cylinders cars and vans.
The major difference between both valves other than their shapes is their operating position. The straight-head valve is always open (plunger is open) while the bent head is closed before power is put in or turned on.
Both types of valves have two-pin connectors with pin-1 being the power supply (12 V socket) while the other being the control wire.
How to check the fuel metering valve?
There are multiple ways to check a fuel metering valve. You can either check it directly by physically accessing the valve. Or use a Scope tool to check the proper functioning of the valve.
Direct inspection of the fuel meter is pretty simple. To check its functioning you can use a multimeter to check its voltage which ideally should be around 3 Ohm. You can also take it out and blow through it to see if the air is passing. If yes, then it is not clogged and working fine.
Another way to physically check is by tapping the fuel meter on your hand. If you hear a tapping sound (the plunger hitting one of the sides) then again it’s not clogged or stuck and is perfectly fine.
A more accurate way to check though is by using a Scope tool and seeing a few readings.
1. Check Volts DC
In the Multimeter section, navigate to Lab Scope > Volts DC. Since your fuel meter starts as you turn on the ignition. You would be able to see constant 0-12V repetitive peaks showing the opening and closing of the fuel meter.
Only when the graph is not consistent, as it either goes high or low, is when your fuel meter valve is malfunctioning.
2. Check Duty Cycle
Again in the Scope Multimeter go to the Graphing Multimeter > Duty Cycle. The duty cycle is basically the ratio of time your fuel meter is on and off. So when your vehicle is idling, it should be constant. However, as you rev, the valve would open more to let more fuel in, so the duty cycle would increase.
Say on idling if the duty cycle was 40%, then while revving it should be 50% – 60%. If that is not the case, then the fuel meter is malfunctioning.
These are two effective methods to quickly check the functioning of a Fuel Metering system using a scoping tool.