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How fuel injection systems work
A detailed explanation of how modern fuel injection systems work and their advantages that help keep fuel mileage and performance under control.

Fuel injection is the biggest advancement to the automotive fuel delivery system since the invention of the automobile, itself. Better fuel mileage, cleaner smelling exhaust, and when was the last time you had to pump the gas pedal 30 times in the middle of winter to get the car started?

Fuel injection also made the Remote Starter possible.

This article will cover both basic systems, though true understanding only comes with time and experience.

There are two different fuel delivery systems, Throttle Body Injection (TBI) and Multi-Port Injection (MPI).

There are variations of these depending on the manufacturer called Computerized Fuel Injection, Port Fuel Injection, Central Fuel Injection and so on, but they are all the same concept as TBI and MPI.

The easiest and first setup to come about was the TBI system in the 1980s.

For over 90 years engines had fuel delivered via a carburetor (carb) where air was drawn in through a small hole - creating a low-pressure center -, which drew fuel from a bowl within the carb. From there the air and fuel mixture was drawn into the individual chambers by vacuum and burned by the spark plugs.

Today, the carb has been replaced by a similar looking ‘Throttle Body’, which contains one or more injectors.

Instead of relying on a low pressure center to move fuel from the bowl of a carb the fuel pump pressurizes the fuel and forces it out as needed.

This way, the computer can control the amount of fuel needed at any given time.

Underneath the Throttle body the fuel and air move to the individual chambers via the intake tunnels just as in a carbureted engine and burned.

There isn’t a lot of science or math to this set up, which makes it easier to install and cheaper - with less parts - overall. There are still drawbacks, however, as you’ll see explained with MPI.

The second delivery system manages fuel flow and efficiency much better than TBI.

Instead of having a carb or TBI unit placed at the central inlet of air, there are several injectors (one per cylinder) placed just at the entrance of the combustion chamber.

Air flows into the engine at the throttle plate and travels down the intake manifold toward the chamber. Just as the air reaches the opening into the chamber an atomized burst of fuel is added to it.

From there, both the fuel and air enter the chamber and are burned to produce power.

The MPI injection system is much more efficient and creates more power this way because there is no loss of fuel to the chamber, meaning the fuel can’t come into contact with the walls of the intake tunnels. This can create a pool of liquid gasoline that doesn’t make it to the burning process and thins out the air/fuel mixture.

Plus, with more injectors and less travel between each nozzle and the chamber the computer can calculate a better amount to add to each individual cylinder. The computer doesn’t have to predict how much fuel will be needed and how much will be lost to the intake walls.

But, how does the computer know when and how much fuel to add?

There is a complex system of sensors on today’s vehicles, most of which are dedicated to fuel delivery and spark (burn) timing.

All of these sensors “talk” to the computer and to each other to “decide” when fuel or spark is to be delivered.

The Crankshaft Position (CKP) sensor monitors a specially tabbed ring on the crankshaft that tells the computer where it is in the firing sequence. “Is the crank at number one?”

The Camshaft Position (CAM) sensor monitors the camshaft (which rotates at one half the speed of the crankshaft) to let the engine know that the mechanical parts are in proper working order and at which stroke the engine is at.

“If the crank is at number one, is this the compression stroke (where fuel would be added) or the exhaust stroke? (Where fuel would be a bad thing).”

The Throttle Position (TPS) sensor measures the angle of the throttle plate, or “How far is your foot pushing the pedal?”

Engine Coolant Temp (ECT) sensors monitor how warm the engine is at any given point. Colder engines require more fuel than warmer ones.

Intake Air Temperature (IAT) sensor let the computer know how warm the air coming into the engine is. The warmer the air, the thinner it becomes. Therefore, it’ll need less fuel mixed with it.

Mass Air Flow (MAF) and Manifold Absolute Pressure (MAP) sensors measure the volume of air, or ‘how much’, is coming into the engine. This is how the computer knows what altitude the car is in relation to Sea Level because, just like with temperature, the higher the altitude the thinner the air.

Knock sensors tell the computer if the spark plugs are firing at the right time. If a spark plug is late, the fuel and air can ignite itself in an uncontrolled manner and do severe damage to the engine.

Finally, Oxygen (O2, or HO2S) sensors are mounted in the exhaust pipes to monitor the burned mixture. Depending on make, model and year there can be between 1 and 4 sensors in the exhaust.

What they are looking for is oxygen content left over after the engine is done with it. If the content is low, the sensors tell the computer to add less fuel. If there is a lot of oxygen then the engine is running ‘lean’ and the computer adds more fuel.

All of these sensors combine their knowledge. The computer looks this all over to determine the best burn mixture for power and how to keep more fuel in the tank instead of wasting it out of the exhaust. It also determines the best way to keep the engine from being damaged due to a lean mix, which can burn up a piston and keeping the mix from being to rich and destroying a very expensive catalytic converter that cleans up the toxic fumes created from the engine.

When the ‘Check Engine’ light comes on the computer is telling the driver that something isn’t right. Either a sensor has stopped working, or the information isn’t right and could be creating damage.

‘Check Engine’ lights aren’t used for practicing with electrical tape.

Written by Douglas Mahn - © 2002 Pagewise

You are here: Essortment Home >> Arts & Entertainment >> Automotive:Repair >> How fuel injection systems work

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DISCLAIMER: PLEASE READ - By printing, downloading, or using you agree to our full terms. Review the full terms at the following URL: http://www.pagewise.com/disclaimer.htm. Below is a summary of some of the terms. If you do not agree to the full terms, do not use the information. We are only publishers of this material, not authors. Information may have errors or be outdated. Some information is from historical sources or represents opinions of the author. It is for research purposes only. The information is “AS IS”, “WITH ALL FAULTS”. User assumes all risk of use, damage, or injury. You agree that we have no liability for any damages. We are not liable for any consequential, incidental, indirect, or special damages. You indemnify us for claims caused by you.

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How fuel injection systems work
A detailed explanation of how modern fuel injection systems work and their advantages that help keep fuel mileage and performance under control.

Fuel injection is the biggest advancement to the automotive fuel delivery system since the invention of the automobile, itself. Better fuel mileage, cleaner smelling exhaust, and when was the last time you had to pump the gas pedal 30 times in the middle of winter to get the car started?

Fuel injection also made the Remote Starter possible.

This article will cover both basic systems, though true understanding only comes with time and experience.

There are two different fuel delivery systems, Throttle Body Injection (TBI) and Multi-Port Injection (MPI).

There are variations of these depending on the manufacturer called Computerized Fuel Injection, Port Fuel Injection, Central Fuel Injection and so on, but they are all the same concept as TBI and MPI.

The easiest and first setup to come about was the TBI system in the 1980s.

For over 90 years engines had fuel delivered via a carburetor (carb) where air was drawn in through a small hole - creating a low-pressure center -, which drew fuel from a bowl within the carb. From there the air and fuel mixture was drawn into the individual chambers by vacuum and burned by the spark plugs.

Today, the carb has been replaced by a similar looking ‘Throttle Body’, which contains one or more injectors.

Instead of relying on a low pressure center to move fuel from the bowl of a carb the fuel pump pressurizes the fuel and forces it out as needed.

This way, the computer can control the amount of fuel needed at any given time.

Underneath the Throttle body the fuel and air move to the individual chambers via the intake tunnels just as in a carbureted engine and burned.

There isn’t a lot of science or math to this set up, which makes it easier to install and cheaper - with less parts - overall. There are still drawbacks, however, as you’ll see explained with MPI.

The second delivery system manages fuel flow and efficiency much better than TBI.

Instead of having a carb or TBI unit placed at the central inlet of air, there are several injectors (one per cylinder) placed just at the entrance of the combustion chamber.

Air flows into the engine at the throttle plate and travels down the intake manifold toward the chamber. Just as the air reaches the opening into the chamber an atomized burst of fuel is added to it.

From there, both the fuel and air enter the chamber and are burned to produce power.

The MPI injection system is much more efficient and creates more power this way because there is no loss of fuel to the chamber, meaning the fuel can’t come into contact with the walls of the intake tunnels. This can create a pool of liquid gasoline that doesn’t make it to the burning process and thins out the air/fuel mixture.

Plus, with more injectors and less travel between each nozzle and the chamber the computer can calculate a better amount to add to each individual cylinder. The computer doesn’t have to predict how much fuel will be needed and how much will be lost to the intake walls.

But, how does the computer know when and how much fuel to add?

There is a complex system of sensors on today’s vehicles, most of which are dedicated to fuel delivery and spark (burn) timing.

All of these sensors “talk” to the computer and to each other to “decide” when fuel or spark is to be delivered.

The Crankshaft Position (CKP) sensor monitors a specially tabbed ring on the crankshaft that tells the computer where it is in the firing sequence. “Is the crank at number one?”

The Camshaft Position (CAM) sensor monitors the camshaft (which rotates at one half the speed of the crankshaft) to let the engine know that the mechanical parts are in proper working order and at which stroke the engine is at.

“If the crank is at number one, is this the compression stroke (where fuel would be added) or the exhaust stroke? (Where fuel would be a bad thing).”

The Throttle Position (TPS) sensor measures the angle of the throttle plate, or “How far is your foot pushing the pedal?”

Engine Coolant Temp (ECT) sensors monitor how warm the engine is at any given point. Colder engines require more fuel than warmer ones.

Intake Air Temperature (IAT) sensor let the computer know how warm the air coming into the engine is. The warmer the air, the thinner it becomes. Therefore, it’ll need less fuel mixed with it.

Mass Air Flow (MAF) and Manifold Absolute Pressure (MAP) sensors measure the volume of air, or ‘how much’, is coming into the engine. This is how the computer knows what altitude the car is in relation to Sea Level because, just like with temperature, the higher the altitude the thinner the air.

Knock sensors tell the computer if the spark plugs are firing at the right time. If a spark plug is late, the fuel and air can ignite itself in an uncontrolled manner and do severe damage to the engine.

Finally, Oxygen (O2, or HO2S) sensors are mounted in the exhaust pipes to monitor the burned mixture. Depending on make, model and year there can be between 1 and 4 sensors in the exhaust.

What they are looking for is oxygen content left over after the engine is done with it. If the content is low, the sensors tell the computer to add less fuel. If there is a lot of oxygen then the engine is running ‘lean’ and the computer adds more fuel.

All of these sensors combine their knowledge. The computer looks this all over to determine the best burn mixture for power and how to keep more fuel in the tank instead of wasting it out of the exhaust. It also determines the best way to keep the engine from being damaged due to a lean mix, which can burn up a piston and keeping the mix from being to rich and destroying a very expensive catalytic converter that cleans up the toxic fumes created from the engine.

When the ‘Check Engine’ light comes on the computer is telling the driver that something isn’t right. Either a sensor has stopped working, or the information isn’t right and could be creating damage.

‘Check Engine’ lights aren’t used for practicing with electrical tape.

Written by Douglas Mahn - © 2002 Pagewise

You are here: Essortment Home >> Arts & Entertainment >> Automotive:Repair >> How fuel injection systems work

< >

DISCLAIMER: PLEASE READ - By printing, downloading, or using you agree to our full terms. Review the full terms at the following URL: http://www.pagewise.com/disclaimer.htm. Below is a summary of some of the terms. If you do not agree to the full terms, do not use the information. We are only publishers of this material, not authors. Information may have errors or be outdated. Some information is from historical sources or represents opinions of the author. It is for research purposes only. The information is “AS IS”, “WITH ALL FAULTS”. User assumes all risk of use, damage, or injury. You agree that we have no liability for any damages. We are not liable for any consequential, incidental, indirect, or special damages. You indemnify us for claims caused by you.

FAQs: This site is published by PageWise, Inc. Would you like to link to this page? Reprint this article on your website? Reprint this article on paper? Want to reference this article in a paper, report, or presentation? Is there an error in this page? Do you have a follow-up question about this topic? Want to read our Privacy Policy? Read our legal/medical disclaimer?

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Troubleshooting car problems can be difficult if you’ve had no training. Professionals charge a lot of money and when you don’t know much about the subject it’s easy for some to take advantage of you. When certain things on a car break, like a door handle, you may be able to postpone the repairs until a better time. Not true with some car parts. Certain repairs require immediate attention. When brakes go bad on a car it’s a dangerous thing. Not only are the passengers of the car at risk but so are pedestrians and other drivers. Some people put off having brakes fixed thinking that they’ll get a little more mileage out of them. Others decide that they’ll drive just a little slower and it’ll be okay for awhile. This is just tempting fate. Brakes should be replaced the moment you suspect there is something wrong with them. Actually, regular check-ups for your car should include testing the brakes to make sure they are good. Manuals usually suggest a certain time period for having brakes replaced and that’s a good idea. Fixing brakes before they go out is the safe way to go.

One minute you can think your brakes are fine but the next, particularly on a rainy day, you could find yourself unable to stop as quickly as you once could. Another initial warning sign that brakes are going to soon need replaced is that you suddenly have to pump them before you can stop. Even if you have to pump the brakes only once, it’s time to have them replaced. Pumping the brakes takes too long when you have to make an immediate stop, risking rear-end collisions with the car in front. Before deciding on new brakes check the brake fluid to make sure you’re not low. If the brake fluid is low fill it up and pump the brakes several times while the car is running. Drive the car slowly in a safe place, like an empty parking lot, to see if they have improved.

A slight sound coming from the wheel area of the car could indicate that the brakes are going bad. The sound will become louder as the brakes become worse and worse. The sound can begin as a ticking sound or can be a grinding sound. Sometimes a squeal when you hit the brakes is the tell-tale sign that they’re bad.

If you stop your car and get out and you happen to notice that there is some smoke coming from the wheel this is not a good sign. Do not drive the car any further. The brakes must be fixed immediately.

You could take your car to have new brakes put on just to find out that instead of needing brakes you only need a brake line. An honest mechanic can fix that problem with little expense but some mechanics might try to charge an unknowing customer for an entire brake job. Learning to spot leaking brake fluid yourself can come in handy. After leaving your car by the curb or in your driveway overnight drive the car forward a few feet then check the road for brake fluid. The spot will look fresh and wet. It might be a small amount but that’s enough to leave your brakes functioning poorly.

The battery is actually the life of your car. Without it’s juice you’ll never leave the driveway. We count on our batteries and actually take them for granted. Regular upkeep on a battery includes checking the water level in it every now and then. This is something that is rarely done unless your car is maintained by a very efficient garage. Many people forget to check the water level which can cause the battery to go dead and leave them stranded. Battery posts, located on the top or side of the battery, can get corroded making it difficult for the battery cables to make good contact. This, too, can leave you stranded.

When you least expect it the last sound you want to hear is the tick-tick-tick of a car that has a dead battery. When you turn the key instead of the usual sounds of the car turning over and firing you’ll sometimes hear a ticking sound and that’s it. In some cases you won’t even get that. You’ll turn the key and there’s nothing. Trouble shoot by checking the water level in the battery and scraping any corrosion from the battery posts. Also remove corrosion from the battery cables. In mild scenarios the battery cable can simply come loose and keep the battery from starting the car. When the cables are loose a screwdriver is usually all you need to be on your way. Simply tighten the cables up on the posts and the car will generally start. Another possibility is that an overhead light got left on all night and ran the battery dead. Try putting a charge on the battery to see if there are future problems or not.

It’s a good idea to carry a jumpstart kit in the trunk of your car for just this sort of situation. The kit allows you to plug into the lighter and get enough juice to jumpstart the car. Or, keep a battery charger handy. It can be plugged into a 110 outlet and will recharge the car’s battery. It takes some time to charge the battery - sometimes several hours.

A hint that the battery could be going bad is that it will stay charged throughout the day while turning it on and off but when using extra power, such as headlights, the car seems to drag when starting. If the car ran fine but refuses to start after using headlights for awhile it could mean that the battery needs replaced.

Another way to determine if your battery is bad is to check the alternator. To do this, start the car then remove the ground cable from the battery. If the car immediately dies this points to a bad alternator rather than a battery gone bad. One other way to test your battery is to place it in a different car to see if it will start. If the car starts and will run for awhile with lights and radio running, the battery is good. If the juice drains rapidly from the battery while running for a short while the battery needs replaced.

Many places that sell car parts will test the battery for you free. They will also sell you a new battery and often install it for you.

If you are reading this article, then your car stereo must need some help. Well, I am here to tell you that there is some hope, if you do not have the funds to take your ride to the local stereo shop and revamp the entire system. You can still do several things to improve the sound quality of your existing system without spending a fortune to get it. Let me explain five cheap improvements you can do that will noticeably improve your mobile listening environment.

The first step you should consider is to improve your existing speakers. Most factory speakers fall short of the sound quality that aftermarket speakers can provide. Immediate improvement to your music can be heard simply by replacing your speakers. All you have to do is shop around for the same dimension speakers as the existing ones in your car. If your car was anything like the ones I had to drive, the factory speakers were nothing more than paper cones. All it took was your little one to poke it with a pencil, and now every artist had been given an instant tracheotomy. It is possible to replace both the front and rear sets of speakers for under $100, and the sound quality improvement would definitely be noticed. Two- or three-way speakers will make a world of difference to your music, especially if your factory speakers were nothing more than simple cone woofers. If you can afford to spend a little more, speaker upgrades are great investments. After all, they are the larynx of your stereo system; better quality speakers can reproduce a much richer sound.

Another relatively inexpensive improvement that can be added to your car stereo is to add a small amplifier. While this addition can get very expensive, if you understand what level of improvement you can get from a particular amplifier, this will also immediately make a noticeable difference. If you have front and rear speakers, a four channel amplifier is best, because you are providing more power to every speaker. If you only need to amplify the front speakers, a two-channel amplifier is the smart choice. The bottom-end price range for two-channel amplifiers is around $80, while four-channel amplifiers start around $120. You may be able to find some slightly cheaper, but as the saying goes: “You get what you pay for.” One important note, be sure to match the speaker ohm rating with the amplifier’s rating. This will optimize the sound quality, as well as prevent you from overdriving either the speakers or the amplifier. Also, check your speakers for maximum power output capabilities. You can purchase an amplifier with a higher power output than your speakers, but you have to be very careful not to set the power output higher than the speakers are capable of accepting. Otherwise, you may be spending more money than you planned, having to buy more speakers!

Let’s say you already have decent speakers, but the main factory CD Receiver deck needs some improvements; it just doesn’t express your individuality. Well, there are many new units on the market that look like they set you back a paycheck or two, but, in reality, were less than $150! These decks offer motorized faceplates that fold down to allow you to insert your favorite CD, and then it closes automatically. That is a nice little feature which gets some attention. What about a deck that can play your MP3 music? This is great because you do not need a Multi-disc CD player to enjoy hours of music. You can have several albums on a single disc.

There is even a unit out there that includes a satellite tuner with your purchase; you only need to purchase the monthly subscription to enjoy 150 channels of commercial-free music, which ties into my fourth inexpensive upgrade option: Satellite Radio. The CD Receiver unit to which I am referring combines two of my cheap upgrade recommendations in one. The monthly subscription for satellite radio starts under $13, and this is a great value when you consider how many listening choices you get for less than 50 cents a day! If you only want to purchase a separate satellite tuner, there are portable units you can take with you wherever you go; they do not limit your musical choices to your vehicle alone. With all the choices available today, it is possible to fit just about any budget.

Now that you have several choices to consider for improvements to your car stereo, let me give you a fifth idea to think about, if you do not need to replace any of your hardware. You have heard, no doubt, the vehicles with excessive bass in the trunk. The vehicle vibrates or rattles with each deep musical note, and it is quite annoying, especially for those outside of the automobile. If it were your vehicle, would you want your car to sound like that, especially after investing a sizeable sum of cash to drown out the rest of the world?

It could be beneficial to add sound dampening insulation to the metal body of your car. It is amazing to hear the difference between the insulated- and non-insulated-metal of your car when subjected to musical bass. In addition, you will reduce or eliminate the unwanted noise created by the vibrating metal, which can interfere with your musical environment. In attempting to improve your musical environment, you would not want to create noise that is directly competing with the very stage you are trying to enhance. There are spray-on, as well as, adhesive-applied insulation on the market, both of which work very well. It may seem somewhat expensive, at first (around $20 per two square feet), but if you can eliminate the little rattles your car has been making because of the music, the return on your investment becomes obvious. And it does not require 100% application coverage for the dampening material to be effective; it can be used sparingly.

Whether you upgrade your speakers, upgrade your receiver unit, add an amplifier, add a satellite radio tuner, or simply insulate your vehicle, your musical environment will be positively enhanced. And, because any one of these choices can be accomplished for less than $150, you won’t have any heartache investing in your automobile’s stereo system. The only heartache you may have is finding the right upgrade for you!