FUEL PRESSURE AND FLOW

THEORY

WHAT IS A FUEL PUMP?

It is an electric pump which is used to pump petrol. This has the electric motor and pump in a common housing and operates whenever the engine is running. If the fuel pump is fitted above the level of the fuel in the tank, an additional low-pressure pump is sometimes located inside the fuel tank; an additional low pressure pump is sometimes located inside the fuel tank to prime the main pump. Some fuel pumps, called dual-stage fuel pumps, incorporate their own feed impellor prior to the positive displacement roller cell for self-priming.

WHAT IS PRESSURE REGULATOR?

The pressure regulator is fitted at the end of the fuel rail. It maintains the pressure in the system high enough for injection. The pressure regulator also maintains a constant pressure differential across the injector. The fuel-pressure regulator is a mechanical unit completely independent of the engine ECU.

FUEL PRESSURE= ENERGY/VOLUME

Extended engine cranking before start-up can indicate a loss of residual fuel pressure, which should remain constant even when an engine has been shut off for several hours. Pressure could be lost on the supply side of the system by a bad fuel pump check valve or a leaking supply line. On the other hand, with a conventional fuel system, it could also be lost by a poorly seated fuel pressure regulator on the return side of the system. To trace a loss of residual pressure, perform a KOEO cycle to pressurize the fuel system, then clamp off supply and return lines one at a time to determine where the pressure is being lost. If pressure still drops after isolating both the supply and return sections individually, the pressure loss could be due to a leaking fuel injector(s). Fuel pressure is merely the amount of force (pressure) measured in pounds per square inch (psi) exerted on the available fuel volume. Most techs are very familiar with measuring fuel pressure with a gauge connected to a Schrader valve located on a fuel injector rail. What you may not realize is that pressure is a one-way street. It can always be reduced but it cannot be increased, unless there’s sufficient volume to sustain it. Using fuel pressure as your only method of fuel system testing means you’re looking at only part of the overall picture.

FUEL FLOW= VOLUME/TIME

Volume and flow are not pressure. A closed faucet has system pressure but no flow. Too often techs rely on fuel pressure readings without realizing that there’s really very little fuel volume flowing through the system. Understanding that fuel pressure is a measurement of force while fuel volume is a measurement of quantity is key. Fuel flow is the volume of fuel a system can deliver over a given period of time. It’s also important to note that any fuel system’s maximum flow capacity is fixed by system design and can never be increased.

PROCESS

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FiFirst of all I wrote the specification it was between 38-44 PSI. Then we turned the key on and started the vehicle and then turned it off. Then I checked if there were any fuel leaks. There were no leaks at all.

·       Then I measured the fuel pressure with the key on but engine off. It came to be 43 PSI. It was under the spec so the fuel pressure was appropriate.

·       Then I measured the fuel pressure with the engine idling. In this one should watch the pressure for a couple of minutes. It came to be 75 PSI.

·       Then with the engine idling I disconnected and connected back the vacuum line going to the fuel pressure regulator. The fuel pressure gauge was reading 48 PSI.

·       Then I turned the engine off. I then waited for five minutes so that I could note my residual or rest pressure. It came to be 42.5 PSI.

·       Then I replaced the vacuum lines. I carefully removed the pressure gauge. Then I turned the key on and off and checked for leaks. Then I started the engine and checked for leaks. The engine was running well and there were no leaks.

REFLECTION

It was very important to know the fuel pressure of your vehicle. The reason being that if the fuel pressure is not appropriate then it cause many problems. Like lack of power, underperforming of car, less fuel efficiency, and it might cause some damage as well.

Thus one should always check that the fuel pressure is always appropriate.