What kind of fuel injection system is best for me?
What is the biggest advantage of fuel injection?
What can I expect for improvement in fuel economy with a fuel injection system?
If you were to compare a fuel injected engine and a carbureted engine, the air fuel ratio is to be considered. Carburetors on many engines are set up to run between 16-17:1 air/fuel ratio. A fuel injection system running on gasoline is controlled to 14.7:1 air/fuel ratio. This intuitively would provide for better economy with a direct fuel injection system than with a carbureted engine. What is also to be taken into account is spark control, acceleration fuel control, and power enrichment. Fuel injection provides for better control in all of these scenarios which for the most part increases overall fuel economy.
Additionally, fuel injected systems almost always stay fine tuned as opposed to a carbureted engine that usually requires a lot of tuning. We typically see an increase in fuel economy between 1/2 and 4 mpg when fuel injection is added.
How much more power can I expect with a fuel injection system?
This is one of the most frequently asked questions. Fuel injection in and of itself provides little or no improvement in power. It does make a difference what type of fuel injection you are using, TBI (throttle body injection) or MPFI (multi port fuel injection). There is some debate over power improvement with fuel injection, however the improvement may have nothing to do with fuel injection.
Fuel injection provides finite control for most of the engines control systems. Since you are able to measure many different operating conditions of the engine and the environment that it is running in, fuel injection allows for precise control of the fuel and the spark. Because of a fuel injection systems constant monitoring, power can be gained due to so many of the engines functions being monitored and controlled through an ECM (electronic control module). This control makes for a very homogeneous fuel charge into the combustion chamber and allows for maximum power to be gained by the combustion process.
TBI systems work very well, especially for the daily driver with a stock or slightly modified engine. They also work very well for motor home and towing applications especially when different altitudes are encountered with your vehicle. These systems are also relatively maintenance free and allow for many hours and miles of low maintenance operation.
MPFI systems are the type of systems where real power gains are realized. This is due mostly to the fact that air/fuel distribution issues are all but eliminated. Also the flexibility of manifold design is infinite. Long runner systems are built to increase low-end torque. With a TBI system you are limited to how you can design the runner length and shape for a wet type manifold. With an MPFI system runners are built with different materials, different shapes, different lengths and varied plenum sizes. All of this different hardware design flexibility allows for more specific camshaft grinds and customer specific manifold variations, all of which increase engine power and torque.
If you have the same engine, same manifold, same conditions and simply add fuel injection along with the same air/fuel ratio and spark advance your power output will be close to the same. With MPFI mainly because of the reduction of air/fuel distribution issues you can usually see 5-10% increase in power. If you add longer runners and a different camshaft design because of the efficiency allowed with MPFI you have significantly increased the power of your engine.
What is included with my fuel injection system? Is your fuel injection system a complete system? Is there anything that is not provided?
Our fuel injection systems are complete with everything that is required for a fuel injection system to work on your vehicle.
TBI systems include:
TBI unit, ECM with specially calibrated chip, custom built wiring harness, external electric fuel pump, fuel pump relay, coolant sensor, MAP sensor and O2 sensor.
MPFI systems include:
Intake manifold and throttle body, fuel rail, and fuel pressure regulator, injectors to match your engine requirements, ECM with specially calibrated chip, custom built wiring harness, external electric fuel pump, fuel pump relay, coolant sensor, air temperature sensor, MAP sensor, vehicle speed sensor and an O2 sensor.
There are a few things that are not provided with your system that you may need to provide. These are:
- Fully electronic distributor or distributor module required for proper input to the ECM. These units are available from AFI for additional cost.
- Throttle cable brackets, you will need to provide your own throttle cable bracket.
- Throttle cable, we do not supply a throttle cable with your system.
- Fuel line, you will need to provide your own fuel line to install your fuel injection system. If you are installing an MPFI system you will need to use special higher pressure line that is available for fuel injection systems.
- Air cleaner, you will need to provide your own air cleaner and air cleaner element.
- Fuel filter, a fuel filter is required before an external fuel pump. Since we do not know exactly how much room you have to install and where you may install the fuel pump you will need to provide your own fuel filter.
- Gasket, you may need to provide your own base gasket and/or manifold gaskets for your system.
- Wire, it may be required to use a small amount of wire for power hook up and possibly fuel pump hook up. We provide some extra wire that you usually can use if needed but you may need to provide a small amount of your own on some sophisticated installations.
How much will my fuel injection system cost?
All of our prices are on the respective pages where the fuel injection system you are looking at is located.
A full TBI system will cost somewhere in the range of $1,000 depending on what options you choose and what your application is.
A full MPFI system will cost somewhere in the range of $2,000 depending again on what options you choose and your application. This price is predominantly for Chevrolet engines.
A custom built MPFI system will start around $3,000 and go up from there.
Are parts for your fuel injection system readily available or are they unique?
Can any engine be fuel injected?
Do I have to program the fuel injection system myself or is it preprogrammed?
Programmable ECM’s are available at significant extra cost.
What is the warranty on my system?
Will I receive technical support after I receive my system?
Can anyone install a fuel injection system, or do I need a professional mechanic?
What is TBI or Throttle Body Fuel Injection?
THROTTLE BODY FUEL INJECTION— The throttle body injection system is one of the first mass-produced fuel injection systems in the US auto industry, and is the most cost efficient system. If not for more stringent emission standards and second generation onboard diagnostics (OBDII), it more than likely would still be widely used. Some of the original designs were developed in the early 70’s by GM’s AC Delco division anticipating the upcoming emissions standards change. Some of the first applications were found with Cadillac in the late 70’s. By 1982 GM was converting most of their powertrains to use this type of system, and was the mainstay of the GM fleet until 1995.
TBI’s use either 1, 2, or 4 fuel injectors and inject metered fuel directly on top of throttle plates much the same as a carburetor. The TBI unit is centrally located on an intake manifold that distributes an air/fuel mixture to each cylinder. GM & Chrysler systems used a low fuel pressure of about 12 psi. Ford used a higher pressure of about 40 psi for their EEC controlled system.
TBI uses a speed density control strategy along with a few electronic sensors to allow a constant monitoring and feedback to the ECM. These signals processed in the ECM control spark advance and fuel metering under all engine operating conditions. TBI equipped vehicles provide excellent drivability, improved fuel economy, and as stated previously are very cost effective. The only draw back of the system is limited intake manifold design.
What is MPFI, Port, TPI and Multi Point Fuel Injection?
MULTI POINT or PORT FUEL INJECTION – MPFI (Multi Point Fuel Injection) uses an individual injector placed directly above the intake valve for each cylinder. This is the most commonly used type of system in today’s vehicles. MPFI allows full compliance with OBDII requirements and produces less HC emissions on cold engine start ups. These systems also eliminate most fuel distribution problems since the fuel is injected directly on top of the the intake valve, and not mixed prior to that point.
One of the biggest advantages of MPFI is the flexibility of intake manifold designs. Most systems are designed with long intake runners, producing more low end engine torque, which is where most daily driving is done. This allows good camshaft grinds for idle stability while providing a drivability advantage. Some of the newer systems are designed with a long and short runner design. A communication valve is placed in the intake manifold that switches between long and short runner depending on the driving condition that you are currently in. The Long runner is for low-end torque and short runner is for higher rpm horsepower.
MPFI can be either speed/density or mass air. Most systems of today are mass air and very expensive to produce. This is because of the # of injectors needed, sophistication of the induction system, and the # of sensors required for proper monitoring and feedback. Another part of this cost equation is the amount of skill and time required to calibrate MPFI systems. There is alot of discussion in the industry as to what is better, mass air or speed/density. We are again seeing some speed/density systems coming out on the market primarily to reduce system cost.
TPI is a GM trade name for Tuned Port Injection. TPI is a multi point injection system with a long runner design that was very popular from the mid 80’s to the mid 90’s. These systems by themselves allowed for more torque and horsepower in the engines they were used on. The long runner design allowed for more low-end torque and even though it limited the amount of high-end horsepower, horsepower was increased with these systems.
What is the difference between SEFI and batch fire or bank to bank? Which one is better?
MPFI systems operate between 30 – 45 psi with one of two different firing strategies. These can be either bank to bank also known as batch fire, or sequential (SEFI). Bank to bank systems fire all or some of the injectors on an engine bank at the same time. A SEFI system fires each injector individually just prior to the fuel being needed for the firing event SEFI systems require extra sensors to determine proper fuel delivery to the correct cylinder at the right time. SEFI systems are used to comply with OBDII requirements and potentially deliver lower emissions. This writer has calibrated both bank to bank and SEFI systems, and found very little emissions advantage with the SEFI system. With the standards being what they are today though, even a .01 gm/mi advantage can be tremendous. (See page for emission requirement discussion).
For most engines that are not being used for high revving race applications batch fire or bank to bank works just fine. SEFI systems as previously discussed require more sensors and are used mainly for emissions and diagnostic requirements. When used for high revving race applications there is more recovery time for the injector with SEFI but you are still running the injector close to a static open condition anyway.
We recommend bank to bank or batch fire for most all applications. We can build you a SEFI system but will be at a higher cost and will not provide any noticeable increase in power or drivability.
What is meant by closed loop and open loop?
OPEN/CLOSED LOOP — indicates the operational mode in which the fuel is being delivered and can also indicate the mode that idle speed is operating in.
OPEN LOOP — Is a predetermined (calibrated) amount of fuel delivered based upon current engine operating conditions. These can be but are not limited to coolant temp., throttle position, engine air flow (map or maf), and time since start. An engine starts up in open loop, after a predetermined time and temperature it will go into closed loop. WOT operation is also open loop to allow for richer A/F mixture required for maximum power.
CLOSED LOOP — Running condition where the exhaust oxygen content is measured with an O2 sensor. A rich/lean signal is relayed to the ECM where it causes a rich or lean command to maintain a 14.7:1 A/F ratio. This rich/lean “dithering” is what creates the full efficiency of a catalytic converter. Gasoline engines are most efficient for emissions constituents at this 14.7:1 A/F ratio
What is meant by speed density and MAF or Mass Air Flow?
SPEED DENSITY— Speed density is a control algorithm which “infers” the amount of air flow into an engine. Incorporating a MAP sensor (manifold absolute pressure), and measuring the engine RPM’s (speed) airflow is calculated. Programmed into the ECM (electronic control module) is a volumetric efficiency table for each specific engine application. This table compares the current engine conditions (speed & pressure or vacuum) and outputs a calculated air flow value. This can now be used to insure the proper amount of fuel based upon the air/fuel requirements of the engine. These systems are very cost effective and work well. The downside is that re-calibration can be required with engine modifications.
MASS AIR FLOW— This system incorporates a mass air flow sensor in between the air cleaner and the throttle body on the intake manifold. This sensor directly measures the precise amount of air flowing into the engine and sends this information to the ECM for proper fuel metering. These systems work very well, are very dependable, but are very costly compared to a speed/density system. More sophisticated air flow control and ducting are required for mass air systems.
Do you use a knock sensor on your systems?
We usually do not use a knock sensor but will upon request. The knock sensor is a device that is used in an attempt for the auto companies to ring out additional fuel economy (usually less than .3 mpg) and still allow for use of almost any fuel that a vehicle may see. The problem with knock sensors is that they can only detect a noise in the block, so any knock be it from lifters, drive chains, etc. will magnify itself as spark knock. Many knock sensor equipped engines falsely retard spark causing a lack of performance than accurately measure spark knock.
Some newer engines use 2 very expensive knock sensors with highly sophisticated control algorithms. These systems still cannot discern engine noise from spark knock.
Do I need to make any modifications to my vehicle to install fuel injection?
The biggest modification that may need to be made is to provide a hole in the firewall to route the wiring harness. This will require about a 1″ hole for clearance needed to pass the connectors into the passenger compartment.
A means to mount the ECM may also be necessary. Brackets, Velcro etc. are all possible means to mount the ECM in the vehicle.
The fuel system will need some modifications that are discussed in another portion of FAQ’s.
If you are converting a carburetor you will not need the fuel pump on your engine and it may be able to be removed and a plate used to cover the hole.
What do I have to do with my ignition system for fuel injection?
Fuel Injection systems provide for the most part a very homogeneous air/fuel charge into your engines combustion chamber. It is also regulated to a stoichiometric air/fuel ratio of 14.7:1. This mixture requires that a very efficient and high energy spark be available to ignite this charge. We therefore do not recommend any systems with a point ignition system.
The most efficient ignition system for your vehicle is a fully electronic ECM controlled unit. A typical standard conventional ignition system, whether it be points or electronic, uses two types of spark advance. A look at your distributor will show you a vacuum advance and mechanical advance. The vacuum advance, usually being an external vacuum, will advance the ignition timing a preset amount dependant on the vacuum of the engine. A mechanical advance is usually a set of counter weights and springs inside of the distributor which advance the ignition timing dependant on the rpm of the engine. A fully electronically controlled ignition system does not have these types of spark advance units but controls the ignition timing through the ECM dependant on engine speed and engine vacuum or load.
The distributor for a fuel injection system is also used for another very important and required component and that is to trigger the ECM to read the engine speed. Engine speed is one of the requirements necessary to determine the proper fueling requirements of your engine. The magnetic pickup in the distributor is used to provide this trigger. For most Chevrolet and GM applications this may be a simple matter of installing a different distributor from a model year where this type of distributor was used. For other applications a custom GM distributor needs to be built and/or an external module is used in conjunction with the magnetic pick-up. When this is the case it is necessary to disable your vacuum and mechanical advance units.
Another popular option is to use an external module like an MSD module and use the tach lead in place of a distributor pick-up. These work very well if you do not want to modify your ignition system since the signal is filtered and usually does not provide any false signals to the ECM.
An option that has been used, but we do not recommend, is the use of a tach signal from a distributor or the “-” terminal of your coil. This type of trigger can falsely trigger the ECM to think the engine is running faster than it really is. When this happens to much fuel is delivered causing other issues with the vehicle. We have successfully used these types of triggers and have a filter that allows this type of ECM trigger to be used. Most people use this option when they do not want to alter the original ignition system.
What changes in my fuel system do I need to make for fuel injection?
The most time consuming and hardest part of installing a fuel injection system is the installation of the electric fuel pump. You will need to install a fuel return line if you do not already have one. There is also an adapter available that can be installed into the fuel filler line for a fuel return. There are other options as well for a return as discussed in the “extreme” section.
The fuel pump needs to be installed as close to the fuel tank as possible. This usually requires the hose from the tank to be replaced to splice the fuel pump into the feed line. A fuel filter also needs to be installed prior to the fuel pump.
Another option and the best option is to install an intank fuel pump. There are companies that make custom fuel tanks for most vehicles with either low-pressure intank fuel pumps for TBI applications or high-pressure pumps for MPFI systems. There are also fuel-sending units complete with the fuel pump available to install into or modify your current fuel tank for proper operation. An intank fuel pump is the recommendation for most systems if it is within your budget.
I have a high overlap, long duration, high lift camshaft, will your system work with my engine?
Camshaft design and specifications are very critical to a fuel injection system. With a mass air system it is less critical since you are measuring the actual amount of air into the engine and controlling the fuel accordingly. Most of our systems are speed/density where the amount of air into the engine is inferred by manifold pressure and engine speed. Since high overlap cams in most cases run a lower vacuum at idle it is difficult to differentiate idle from a loaded condition.
There are MAP sensors which allow for the ECM to be “tricked” at idle in an attempt to control this type of situation. We prefer that your engine use a camshaft duration of less than 220 deg at .050″ of lift. This can be a little longer for larger displacement engines; please write with your cam specs if you believe that there may be an issue.
I have dual fuel tanks, do I need two fuel pumps?
How long will it take for me to receive my fuel injection system?
Do I need to keep my air pump with fuel injection? How about my EGR?
EGR valves again are not needed unless you need to meet emissions or just want to keep the emission levels of your engine as low as possible. EGR can also add to the fuel economy of your vehicle so retaining EGR is not a bad thing to consider.
How long will it take for me to install a fuel injection system?
The different systems will take different amounts of time. An MPFI system requires an intake manifold change where as a TBI system usually does not unless you request a higher flow manifold. The most difficult part of the installation is usually the fuel pump. An external fuel pump is provided with your system that requires mounting near the fuel tank. More discussion on the fuel pump is included in fuel system modification requirements. For the average person taking their time it should take a full day or so to install, it would not be unheard of to installit in much less time or a full weekend either.
Can I mount the ECM in the engine compartment of the vehicle?
I do extreme off road and rock crawling, does fuel injection keep my engine running under extreme conditions?
Probably the easiest way to solve this issue with most vehicles is to run with a full fuel tank.
One-way is to provide a small reservoir of fuel that would always be full and mounted ahead of the fuel pump. This reservoir can be filled using an additional small electric pump or even the engines original mechanical fuel pump. This way if the pickup in the tank should be in a dry position for even a short time there will be no interruption of fuel flow.
Another option, and some vehicles already have them, is to use baffled tanks or fuel cells. This allows for low or no sloshing of the fuel and again keeps the pickup fully submersed at all times.
What do I do if I change something on my engine and it requires a new chip?
I have some of my own components, can you build me a system around this?
If you choose to install a system in which you have procured your own components we obviously cannot guarantee the results. We do not have any way to check for the proper operation of the components that you have acquired. We can refurbish TBI units and injectors for an additional charge to help you with your project.
What is Direct Fuel Injection?
My state has emission inspections; will your system meet emission standards?
California can be difficult in some instances. If you upgrade your system to fuel injection from a carburetor you will need to meet the emission standards that the fuel injection system was built for. This means that we can build your system to meet 1990 emission standards. For stock and only slightly modified engines this should not be a problem. We do not make any guarantees that your vehicle will meet emission standards with an Affordable Fuel Injection system. We do need to know though if you are going run the system through the emissions test station.
What is OBD and OBDII?
OBD stands for Onboard Diagnostics and OBDII stands for 2nd generation Onboard Diagnostics. In the early 90’s CARB (California Air Research Board) and the federal government realized that even with the most sophisticated emission controls and standards, it is all for naught if the system is not working properly. The result is a requirement to monitor all emission functions and alert the operator if any of these systems fails to serve its proper function (usually through the illumination of a Service Engine Soon or Check Engine light). Also in the regulation are requirements to have the Onboard ECM make some corrective actions that would still provide for some default signal to keep emissions to a minimum with inoperable components. A third requirement is a generic connector that allows for all vehicles to have basic common diagnostic trouble codes, connection, generic information of basic engine functions and the ability to access them with standard diagnostic equipment.
OBD has required billions of dollars of investment from the automotive industry and has greatly increased the reliability of emission equipment.
What is meant by TLEV, LEV, ULEV, CAA?
You may read this on vehicles and/or see them on stickers that the auto manufacturers have put on vehicles. These are emission standards that are required for the standard that the vehicle has been calibrated and built to.
CAA stands for Clean Air Act. This is the first requirement of emission reduction since 1980 and was enacted in the early 90’s. Some vehicles, mostly low volume specialty vehicles are still only calibrated to CAA standards.
LEV and LEVII stands for Low Emission Vehicle. LEV was the prevailing standard for most of the vehicles built in the early 2000’s.
LEV standards in this writers opinion have made a significant impact on cleaner air and should be the prevailing standard for all vehicles. Going to lower standards only requires billions in investment with diminishing returns. To give you an idea of where we have come and where we are at lets look at the standards.
1975 found the first lowered emission standards that required a catalytic converter and electronic ignition. Hydrocarbon emissions are the lowest and hardest to meet so that is the constituent that we will discuss. The other emission constituents have also been greatly reduced in similar amounts. The HC (Hydrocarbon) standard at that time (1975) was 2.0 gm/mi. This standard changed to .410 gm/mi in 1980. This was a significant reduction and required fast and immediate actions to meet them with technology available in the day. This standard prevailed through the 80’s with the auto companies developing better and better ways to meet the standards, increase fuel economy and reducing the cost of emission components required on the engine.
In 1990 CAA was enacted which brought HC emission standards to .310 gm/mi. TLEV requirements were .16 gm/mi while LEV emission requirements are .1 gm/mi and ULEV requirements are .075 gm/mi.
With today’s technology in catalytic converters and control strategies these requirements are possible. But also remember now that 95% of the emissions emitted from and engine happen within the first 30 seconds of operation. After 30 seconds many catalytic converters have “lit off” and convert 99% or more of the emissions emitted from the engine. To bring down the emission requirements of an engine will be a major undertaking as well as billions more dollars in investment. In this writers opinion this money is better spent on newer technology that will reduce green house emissions and improve economy of the vehicles. Fuel cells, natural gas, electric and hybrid vehicles all fall into this equation. Emission standards are at a point of diminishing returns. The next time that you hear a politician tell you that this new standard will reduce emissions by 30% remember what it is, 30% of. 30% of a 2.0 gm. Standard was significant while 30% of .075 is relatively less significant.