The Fuel Injection about Carburetor (3)
If you’re not so concerned about tradition when building your next hot rod or custom project and the thought of tuning multiple Strombergs every other weekend doesn’t whet your appetite, then going with electronic fuel injection may be for you. Although cost and complexity are greater than with carburetors, even on a car like 1928-34 Ford, there are many benefits of going with EFI. For starters, once the engine and fuel system have been fitted and tested, they require minimal maintenance.
The Case for Fuel Injection
If you’re not so concerned about tradition when building your next hot rod or custom project and the thought of tuning multiple Strombergs every other weekend doesn’t whet your appetite, then going with electronic fuel injection may be for you. Although cost and complexity are greater than with carburetors, even on a car like 1928-34 Ford, there are many benefits of going with EFI. For starters, once the engine and fuel system have been fitted and tested, they require minimal maintenance. Problems associated with carburetors, including rough idling, cold weather starting and excessively rich mixtures are virtually eliminated, because EFI systems allow for a much more precise fuel delivery which is exactly tailored to the amount of air entering the engine.
The reasons why fuel injection has become so widespread, at least from an OE standpoint, go back to emissions requirements instigated in the 1970s. In order to reduce the output of harmful exhaust gases, more precise control and metering of air/fuel mixtures were required. In order to successfully achieve this, oxygen sensors, placed in the top of the exhaust stream, relay the level of O2 passing through back to an electronic engine control module, which then precisely adjusts the air/fuel ratio in real time. Also known as closed loop control, this requires more precise fuel delivery, simply not possible with carburetors and their relatively crude fuel jets and air flow control. As a result, fuel injection came to the forefront.
Early systems used injectors placed atop a central hole in the intake manifold (much like a carburetor), but have been supplanted by sequential injection which completely separates the air and fuel paths, drawing the former in through the top of the engine via a throttle body and a manifold with individual intake runners and then squirting the fuel in via a rail linked to individual injectors for each cylinder at the bottom of the manifold. Because of the need for more precise fuel delivery, much greater fuel pressure is required (usually between 40-45 psi – versus 8-9 psi for carbed systems); hence EFI systems use high pressure lines and a high volume, electrically-operated pump, often with a main and return fuel line (that draws excess fuel back to the gas tank). The pump can be externally or internally mounted, but for quieter operation and reduced maintenance, pumps mounted in the tank itself are becoming increasingly popular (the fuel also cools the pump, extending operating life).
Getting the Right Components
When it comes to building a hot rod or custom with electronic fuel injection, choosing the right donor car is critical. Central to the EFI system is the engine’s electronic control module which, via air intake temperature sensors, throttle position sensor and manifold absolute pressure sensor, precisely monitors the flow rate of air into the engine. Using this data, the ECM consults its internal look up tables to match the flow rate of fuel to achieve the Stochimetric ideal of 14 parts air to 1 part of fuel. When you’re considering EFI, you need to get your hands on a complete system, ECU, wiring harness, fuel rails and injectors, plus determine if you’ll need new fuel lines, fittings and an electric fuel pump.
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