Engine/Fuel Management

Unobstructed air/fuel flow is critical to optimum engine performance

Achieving and maintaining an optimum air-fuel ratio in an engine to deliver the best performance requires that the air and fuel entering the engine combustion chamber be free of any contaminants. It is ironic that as the technology improved to enhance the fuel charging system of an engine to deliver increased power, increased fuel economy and lower emissions, the air and fuel mixture entering the combustion chamber became less clean. To best understand the level and type of contamination and how it affects the flow of air and fuel, we must review the evolution of fuel management systems introduced in vehicles during the past 50 years.


Prior to the early 1970’s most mass produced vehicles were equipped with an effective but crude fuel management device. The carburetor came in a multitude of shapes and sizes (single barrel, two barrel and four barrel designs). A carburetor controls both the flow or air and fuel into the engine. When the cost of gasoline was not of any concern to most people and emission management a thing of the future, the carburetor served its purpose in delivering the performance needed to power the vehicles of the time. Carbureted engines were simple in design and remain fairly clean except for a small amount of air borne contaminants (air, moisture, pollen and dust) getting past the air filter to contaminate the throttle plate, venturiis and linkages.

 Emission Standards – Government emission regulations and its effect on engine and fuel management design

This changed dramatically in the mid 1960’s as the first generation of emission regulations was implemented. The addition of a Positive Crankcase Ventilation valve to the engine stopped the venting of crankcase gases (containing oil, varnish, acid, gasoline, etc…) into the atmosphere and redirected them to the air intake system. Early designs had these gases enter into the air filter intake tube allowing the filtration system to remove some of the impurities from the incoming air. The new emission regulations required the vehicle manufacturers to re-directed the crankcase gases into the engine’s combustion chamber for burning via the intake manifold. This design which is still in place today permits the contaminants entering the engine to settle anywhere in the intake system thus affecting the air and fuel flow. Due to the simplicity in design, the process for cleaning and removing contaminants in the air intake was and continues to be a relatively simple and economical process.

Throttle Body Fuel Injection

The gasoline shortage crisis of the early 1970’s created the first wave of rapid gasoline price increases. As a result the automotive manufacturers of the time realized that carburetion design had reached its peak in its ability to deliver optimum power, fuel economy and lower emissions as required by government regulations. The first generation fuel injection system known as throttle body or central fuel injection was introduced as a technology to meet the newly mandated fuel economy and emissions release requirements. The design was simple and cost effective. The basic design looked very much like a carburetor body with all of the complex valves and levers removed and replaced with a centrally placed fuel injector. As was the case in the carburetor fed engine, the throttle body also managed the flow of air and fuel into the engine.

This design allowed the manufacturers to incorporate feedback and control technology managed by a simple computer the flow of air and fuel into the engine, thus providing improved fuel economy and lower emissions as mandated by various government agencies. However the engines produced during this period had much lower compression ratios and delivered much less power.  This was not the most satisfactory system but met the requirements of the time. The new fuel injected system worked well however was also plagued with the crankcase contamination issues as experienced with the carbureted design. The throttle body’s simple design made it easy to service and maintain and economical to service however the design life of the system was short lived as it was not able to keep abreast of the ongoing legislated increase in fuel economy and lower emission standards.

Multi Point Fuel Injection (MPI)/Electronic Fuel Injection (EFI)

This design which was once coveted and restricted to high performance and luxury vehicles became affordable to almost any class of vehicle. The MPI/EFI design included a fuel injector for each cylinder within the intake manifold located very close to the intake valve. Unlike the previous generation of fuel management systems (carburetor and throttle body) an MPI/EFI system incorporated a throttle body but this design did not control any flow of fuel into the engine. It is restricted to the flow of air. Since this system is managed by a sophisticated computer program, air and fuel entering the cylinders could be precisely managed thus delivering better performance (compression ratios improved), fuel economy and lower emissions.

As experienced in previous generations of fuel management systems, the MPI/EFI fuel management system is affected as well with the PCV re-direction of crankcase gases into the intake manifold to be mixed with the incoming air and injected fuel, the varnish, oils, acids, etc… also contaminated the manifold surfaces, causing restrictions in the injector tips and fouling spark plugs. Several types of specialized intake system and fuel injector management service equipment have been developed to clean the intake manifold, intake valves and fuel injectors.

Direct Fuel Injection

A new generation of fuel management for gasoline powered vehicles has appeared in the market during the past several years. The technology is not a new technology however it is a technology that has been part of diesel engineered engines for decades. Direct injection is a design technology that continues to incorporate a throttle body that strictly controls air flow but it introduces fuel directly into the combustion chamber. This system is part of a sophisticated electronically managed system that is very precise in that it delivers fuel in the exact requirement for the power demands of the engine. This system permits manufacturers to significantly deliver increased power, increased fuel economy and much lower emissions.

DI engines are also designed with a PCV system that re-circulates crankcase gases back into the intake manifold and into the engine for burning. As experienced in all other generations of fuel management systems, the contaminants coat the intake manifold with a viscous deposit and the intake valves with a hard mass build-up of baked on oil, wax, varnish and dirt. These contaminants impede the flow of air into the engine which over time will affect the overall performance of the engine.


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