Multipoint - EFI System (Part4. FUEL RAIL ASSEMBLY)

The fuel rail assembly, also called a fuel log, feeds fuel to all of the injectors, Fig. 3.11. The fuel pressure regulator and sometimes the cold-start injector attach to the fuel rail. The fuel rail can be a length of steel tubing or a cast metal block.

As shown in Fig.below, fuel enters the fuel rail from the electric fuel pump. Equal fuel pressure forms inside the rail and at the inlet to each injector. The pressure regulator bleeds off excess fuel to maintain the proper pressure in the system. This allows cool fuel to con­stantly circulate between the fuel rail and the fuel tank.
A service fitting is a threaded orifice for bleeding off pressure and for installing a pressure gauge. One is normally provided on the fuel rail. It is usually covered with a metal cap that keeps out dust and dirt.

Fuel rail assembly. Fuel pressure regulator and sometimes cold-start injector are considered part of this assembly. (Buick)

Electric fuel pump supplies fuel to fuel rail. Note that this rail consists of a length of tubing rather than a casting. (Fiat)

Multipoint - EFI System (Part3. GASOLINE INJECTION)

An injector for a gasoline injection system is simply an electrically operated fuel valve. When energized by the computer, it must open and produce a uniform fuel spray pattern in the intake manifold. When re-energized, it must close quickly, without leakage.

Injector Construction

Most modern injectors are made of metal and plastic. Rubber O-rings seal joints where parts fit together. Usual­ly, the injector fits into a hole machined into the intake manifold. However, as will be discussed in the next chapter, some systems have the injector in the throttle body assembly.

Cutaways show important components of an injector. (Chrysler)

Refer to this illustration.

1. ELECTRIC TERMINALS (electrical connection for circuit between injector coil and computer).
2. INJECTOR SOLENOID (armature and coil that opens and closes valve).
3. INJECTOR SCREEN (screen filter for trapping debris before it can enter injector nozzle).
4. NEEDLE VALVE (end of armature shaped to seal against needle seat).
5. NEEDLE SEAT (machined surface around the hole in end of injector against which the needle valve tip presses to form a seal).
6. INJECTOR SPRING (small spring that returns nee­dle valve to closed position).
7. O-RING SEAL (rubber seal that fits around outside of injector body and seals in intake manifold).
8. INJECTOR NOZZLE (injector outlet that produces fuel-spray pattern).

EFI injector operation. A-Current through injector coil builds magnetic field. Magnetism attracts and pulls up on armature to draw injector needle off its seat. Gasoline sprays out. B-Current flow stops when computer breaks circuit. Injector valve closes stopping fuel spray.

Gasoline Injector Operation

In a simplified way, Above picture illustrates the operation of a gasoline injector. When the computer sends current to the injector coil, the coil develops a magnetic field. Like an electromagnet, the field attracts and pulls on the injector armature. The armature moves up into the coil's field. The needle is then lifted off its seat and let’s fuel spray out the nozzle into the intake manifold.
When the computer shuts off current to the injector coil, the magnetic field collapses. This lets the injector spring push down on the armature forcing the needle against its seat. This blocks fuel flow.

Injector Pulse Width

Injector pulse width refers to the length of time or dura­tion that the injector is open. The computer controls injector pulse width. A long pulse width richens the fuel mixture because more fuel would spray into the intake manifold on each cycle. A short pulse width would lean the mixture because the injector would be kept closed longer between pulses.

Injector pulse width means the amount of time that computer sends current to injector to keep valve open. A-Short pulse causes less fuel spray because injector valve is not open long percentage of time. Mixture is leaner. B-Long pulse keeps valve open more of the time. Mixture is richer

Above picture illustrates short and long injector pulse widths. Note that the square sine wave (sine represent­ing voltage change) denotes the pulse width. When the wave moves up from zero, indicating voltage supply to the injector, the injector is open. When the wave moves back down to zero (base line), the injector is closed because there is no voltage and current flow.
When the square wave is shorter, Fig.A, the injector pulse width is shorter and the fuel mixture is leaner. When the square wave is longer, Fig.B, the pulse width is longer and the mixture is richer.
With many systems, the computer cycles the injec­tors open and closed several times a second. By chang­ing the percentage of ON and OFF times, it can control the air-fuel mixture ratio.

Multipoint - EFI System (Part2. ELECTRONIC CONTROL UNIT (COMPUTER))

The computer, or electronic control unit (ECU), is the "brain" of the fuel injection system. The sensors and wiring harness serve as the "nervous system": check­ing temperatures, positions, and other considerations for proper injection system operation. Fig below shows how electric current is fed to the computer from various sensors and how the computer feeds current to the injectors.
A car's computer is actually a preprogrammed micro­computer (preset, miniaturized electronic circuit). It has microscopic electronic circuits which are formed inside integrated circuits (ICs).
An integrated circuit is an electronic chip or circuit manufactured by photographically reducing a circuit and placing it on a special semiconductor (transistor type) material. This enables the computer to have literally hundreds or thousands of transistors, resistors, capacitors, and similar components in a very small space. Different circuits are provided in the computer for per­forming different functions.

Engine sensors send flow of information to electronic control module (on-board computer) in form of small electric currents. The module, acting on signal received, feeds current that operates injectors.

On-board computer contains thousands of miniaturized circuits.

The picture is showing a photo of the inside of an automobile computer. Note the very small components, especially the integrated circuits.
The on-board computer is about the size of a car radio and is often placed in the passenger compartment. Since computers are sensitive to vibration, extreme tempera­ture change, and moisture, they are sometimes located behind or under the dash panel, Fig.3.7. This places them away from engine heat, moisture, and the elements in the engine compartment.
There are four basic parts or sections to a car's com­puter: input/output devices, central processing unit, power supply, and memories.

Input/output Devices

The input/output devices are electronic circuits that convert signals from sensors into digital (on/off or com­puter) signals for use in the central processing unit (brain or calculator section) of the computer. The devices (cir­cuits) can also change computer language into electrical signals to operate system components.



On-board computer is usually behind instrument panel (dash). In this location, it is shielded from damaging engine heat and vibration. Some computers are mounted on air cleaner or elsewhere in engine or passenger compartment. (Cadillac)

Central Processing Unit

The central processing unit performs mathematical functions or logic functions to deliver the correct air-fuel ratio and to operate other system devices. It uses digital signals from the input devices to determine what is going on during vehicle operation and what should be done to increase efficiency.

Power Supply

The power supply in a car's computer prevents voltage fluctuations that could affect computer operation. A computer relies on very smooth dc current, mainly from the car battery. The power supply simply regulates in­put voltage to other parts of the computer.

Computer Memories

Most computers have three basic types of memory circuits: read only memory, random access memory, and programmable read only memory.

The read only memory (ROM) is programmed data that can only be analyzed by the computer itself. It is infor­mation used by the computer in performing the various functions. The ROM program cannot be changed. If the battery or voltage supply is disconnected from the com­puter, the data in the ROM will remain in the computer.

The random access memory (RAM) is temporary in­formation held in the computer. It is like a "note pad" of inputs and outputs. Data such as self-diagnosis codes can be pulled out of RAM. If battery voltage is removed, all information is erased from RAM.

The programmable read only memory (PROM) has in­formation on the particular make and model car. It has data about engine size, vehicle weight, transmission type, rear axle ratio, etc. As you will learn in the chapter on fuel injection service, the PROM is normally removed and reused when replacing the central processing unit (computer). If voltage is disconnected from the PROM, it will retain its information.

Multipoint - EFI System (Part1. FUEL INJECTION)

Fuel injection is a means of metering Fuel into an internal combustion engine. In modern automotive applications, fuel metering is one of several functions performed by an "engine management system". For gasoline engines, carburetors were the predominant method to meter fuel before the widespread use of fuel Injection. However, a wide variety of injection systems have existed since the earliest usage of the internal combustion engine. The primary functional difference between carburetors and fuel injection is that fuel injection atomizes the fuel by forcibly pumping it through a small nozzle under high pressure, while a carburetor relies on the vacuum created by intake air rushing through it to add the fuel to the air stream. The fuel injector is only a nozzle and a valve: the power to inject the fuel comes from further back in the fuel supply, from a pump or a pressure container.

A modern gasoline injection system, using pressure from an electric fuel pump, sprays fuel into the engine intake manifold. See Fig below. Like a carburetor, it pro­vides the correct air-fuel mixture for specific engine operating conditions. However, PRESSURE, not engine vacuum (suction), feeds the fuel into the engine cylinders. This makes gasoline injection very efficient.

Gasoline Injection Advantages

Gasoline injection has several advantages over a car­buretor. The most important of these are:
Improved atomization. Fuel is forced into the intake manifold under pressure. This helps break the fuel into a fine mist.
Better fuel distribution. Flow of fuel vapors to each cylinder is more uniform.
Smoother idle. A leaner fuel mixture can be used without rough idle because of better fuel distribution and low-speed atomization.

Simplified cutaway shows action of most common fuel injection system for a gasoline engine.

1. Improved fuel economy. Efficiency is high because of more precise fuel metering, atomization, and distribution.
2. Lower emissions. Lean, efficient air-fuel mixture reduces exhaust pollution.
3. Better cold weather operation. Injection gives bet­ter control of mixture enrichment than a carburetor choke.
4. More engine power. Precise metering of fuel to each cylinder and increased air flow can produce more horsepower.
5. Simpler. Late-model, electronic fuel injection systems have fewer parts than modern computer controlled carburetor systems.

Gasoline Injection Timing

The timing of a gasoline injection system relates engine valve action to the time when fuel is sprayed into the engine intake manifold. There are three basic classifications of gasoline injection timing: intermit­tent, timed, and continuous. An intermittent gasoline injection system opens and closes the injection valves independently of the engine intake valves. This type of injection system may spray fuel into the engine when the valves are open or when they are closed.
Another name for an intermittent injection system is MODULATED injection system. This is one of the most common types of gasoline injection. A timed injection system squirts fuel into the engine right before or as the intake valves open. It is timed to the opening of the engine intake valves. The best example of timed injection is a diesel injection system.
A continuous gasoline injection system sprays fuel into the intake manifold all of the time. Anytime the engine is running, some fuel is forced out of the injec­tor nozzles and into the engine.
The air-fuel ratio is controlled by increasing or decreasing fuel pressure at the injectors. This increases or decreases fuel flow Out of the injectors. A con­tinuous type injection system is frequently used on several foreign cars and on a few American cars.

Note four subsystems of an electronic gasoline injection system (dashed line boxes). Sensor systems feed data to computer. Computer uses this data to operate fuel delivery system. Parts of air system can a/so be controlled by computer.

Fuel Delivery System

The fuel delivery system cleans and meters the right amount of fuel for varied driving conditions. It is made up of an electric fuel pump, fuel filter, fuel rail, pressure regulator, injectors, and connecting lines and hoses.
The electric pump forces fuel out of the tank, through the lines, and into the pressure regulator. When the com­puter energizes the injectors, fuel sprays into the engine. Extra fuel bleeds out of the pressure regulator and back to the tank.
Note: Many of the parts (fuel pump, filters, lines, etc.)

Air Induction System

An air induction system for Electronic Fuel Injection provides clean air and delivers it to the engine cylinders. This system, typically, consists of an air filter, throttle body, throttle valve, intake manifold, and connecting air ducts.

Design of air induction systems will vary depending upon engine and fuel system design. However, they all have an air filter for removing airborne impurities, a throttle valve for controlling air flow into the engine, and other related parts.

Sensor System

The Electronic Fuel Injection sensor system keeps track of engine operating conditions and passes this information to the computer. See Fig below. A typical Electronic Fuel Injection sensor system includes an oxygen (exhaust gas) sensor, engine coolant tempera­ture sensor, air inlet temperature sensor, throttle posi­tion sensor, intake manifold pressure (vacuum) sensor, and other sensors.
Just as your body can sense a change in its surround­ings, (touching a hot stove for example), the sensor system can sense a change in the operation of many vehicle systems. It enables the modern fuel injection system to CHECK and CORRECT itself.

These diagrams summarize computer control system. A-Computer or ECU inputs. B -ECU (electronic control unit] outputs of various system parts. (Renault)

Computer Control System

The computer control system processes information and controls operation of the Electronic Fuel Injection system and certain other automobile systems.
A computer wiring harness carries current to and from the computer. Sensors from the engine, transmission, air conditioning system, and other systems send elec­trical information to the computer through the harness. Then, the computer can operate the injectors, transmis­sion, ignition system, emission control systems, and other components for maximum efficiency.

CURCUIT CELLAR (JANUARY 2011) ISSUE 246

Content : Embedded Applications, MCU-Based Brake Control system, Mobile Application Development (A Sound Detection Algorithm), Stress Free Probing, Embedded energy Conservation, “smart” network Access explained, Surge disaster preparedness Tips.

Click Here To Download

Cypress Warp 6.3

Warp users describe electronic designs using VHDL and then compile and synthesize those descriptions to program Cypress devices, such as small PLDs, MAX340 EPLDs, FLASH370, Ultra37000, Delta39K and Quantum 38K CPLDs.
Warp consists of :
• The Warp VHDL IEEE 1076/1164 compliant compiler to translate VHDL text descriptions into JEDEC files that can be mapped onto programmable devices.
• On the PC platforms, Warp also contains an FSM editor and Active-HDL Sim, the post-synthesis timing simulator from Aldec, Inc.



Click link below to download Cypress Warp 6.3

Cypress Warp 6.3 With Serial.zip.001
Cypress Warp 6.3 With Serial.zip.002
Cypress Warp 6.3 With Serial.zip.003
Cypress Warp 6.3 With Serial.zip.004
Cypress Warp 6.3 With Serial.zip.005
Cypress Warp 6.3 With Serial.zip.006
Cypress Warp 6.3 With Serial.zip.007
Cypress Warp 6.3 With Serial.zip.008
Cypress Warp 6.3 With Serial.zip.009
Cypress Warp 6.3 With Serial.zip.010
Cypress Warp 6.3 With Serial.zip.011

Honda Civic (96-98) Service Manual

This service contains information for the 1996 - 1998 Honda CIVIC. It is devided into 24 sections. The first page of each section is marked with a black tab that lines up with its corresponding thumb index tab on this page and the back cover. You can quickly find the first page of each section without looking through a full table of contents.

The main chapter are covered : General Info, Special Tools, Specifications, Maintenance, Engine, Cooling, Fuel and Emissions, Transaxle, Steering, Suspension, Brakes (Including ABS), Body, Heater and Air Conditioning, Electrical, and SRS.

Click link below to download.

Honda Civic (96-98) Service Manual.zip.001
Honda Civic (96-98) Service Manual.zip.002
Honda Civic (96-98) Service Manual.zip.003
Honda Civic (96-98) Service Manual.zip.004
Honda Civic (96-98) Service Manual.zip.005
Honda Civic (96-98) Service Manual.zip.006
Honda Civic (96-98) Service Manual.zip.007
Honda Civic (96-98) Service Manual.zip.008

Serial Port Test Utility With "Visual Basic 6.0" Code (Programming Serial Port With Visual Basic 6.0)

This is a preliminary serial port test utility. The scope of the project has drifted from a simple test app to a full utility. I am releasing the code as a beta test and to attempt to get some feed back. I understand that the structure of the design is not "robust" as this project's scope has wandered. My primary concern is to determine the functionallity likes and dislikes from other programmers needs. The final version will include Text file logging of data sent and received. Please feel free to make suggestions for improvements. The basic functionality of the code has been tested on both Win NT and Win2000. Note that all the error handling is not complete nor has the app been tested by anyone but me.

Click Here To Download

Low Cost (8-Channel) Thermocouple Signal Conditioning With Analog Multiplexer and Analog Optocoupler.

In the current project will be created a signal conditioning for thermocouple equipped with an analog multiplexer, the total input for this circuit is 8-channel thermocouple input.

Some of the problems in a thermocouple signal conditioning is required strengthening gain and also giving a pretty good filter so the noise do not stay in the thermocouple which has a weak signal.

Some of the main components in this project are:
1. Multiplexer Analog Input For Thermocouple (ADG507A)
2. Thermocouple Amplifier (AD595)
3. Op-Amp (INA126)
4. Analog Optocoupler (HCNR201)



ADG507A



The ADG507A are CMOS monolithic analog multiplexers with 16 channels and dual 8 channels, respectively. The ADG507A switches one of eight differential inputs to a common differential output, depending on the state of three binary addresses and an enable input. Both devices have TTL and 5 V CMOS logic compatible digital inputs. The ADG507A are designed on an enhanced LC2MOS process, which gives an increased signal capability of VSS to VDD and enables operation over a wide range of supply voltages. The devices can operate comfortably anywhere in the 10.8 V to 16.5 V single or dual supply range. These multiplexers also feature high switching speeds.


AD595



The AD595 is a complete instrumentation amplifier and thermocouple cold junction compensator on a monolithic chip. It combines an ice point reference with a precalibrated amplifier to produce a high level (10 mV/°C) output directly from a thermocouple signal. Pin-strapping options allow it to be used as a linear amplifier-compensator or as a switched output setpoint controller using either fixed or remote setpoint control. It can be used to amplify its compensation voltage directly, thereby converting it to a stand-alone Celsius transducer with a low impedance voltage output.

You can see the AD595 output voltage as a representation of the temperature thermocuople complete in datasheet. The Appropriate thermocouple type for the AD595 is J and K-type thermocouple.


INA126



The INA126 is precision instrumentation amplifiers for accurate, low noise differential signal acquisition. Their two-op-amp design provides excellent performance with very low quiescent current (175μA/channel). This, combined with a wide operating voltage range of ±1.35V to ±18V, makes them ideal for portable instrumentation and data acquisition systems. Gain can be set from 5V/V to 10000V/V with a single external resistor. Laser trimmed input circuitry provides low offset voltage (250μV max), low offset voltage drift (3μV/°C max) and excellent common-mode rejection.

You can see the basic connection and how to setting the gain for INA126 in the picture below.




How The Circuit Work

The complete picture thermocouple signal conditioning circuit as shown below.



Instal the thermocouple sensor in the channel that you want on the input terminals. For example if you want to put on channel 1 you can plug thermocouple in the terminal J1. Do addressing for ADG507A multiplexer in accordance with the input channel that you want. For reference ADG507A addressing you can use the reference to the ADG507A datasheet which you can download at the bottom part.

Thermocouple output on this ADG507A will be given to the AD595 as an information signal from the thermocouple. ADG595 will process this data and then converted and amplified into a voltage that represents the signal from the thermocouple. The magnitude of this voltage can you see on the AD595 datasheet.

The output of the AD595 is still too small so need to be strengthened again using the INA126 op-amp, Set INA126 Gain by adjusting the value of VR1 to get the gain that you want. Do not forget to set the offset of the INA126 with setting VR2, adjust VR2 until the voltage at pin5 of ICINA126 = +/- 0 Volt.


HCNR201



Actually the output of the INA126 is good enough to be used, but sometimes there are problems when the tip of this thermocouple we attach to the body of the equipment that containing the ground, therefore in this series are equipped with analog isolatar HCNR201 to isolate the output voltage of the INA126 to not blend with another ground. In the picture you can see, there are two power supply that is VCC1 and VCC2, VCC1 is devoted only to the Thermocouple where ground VCC1 (GND) should not be fused with the another ground, GND is ground only for a series of ADG507A, AD595 and INA126. While VCC2 with ground GNDA is ground that can be associated with other equipment such as ground on data acquisition board.

HCNR201 is high-linearity analog optocoupler consists of a high-performance AlGaAs LED that illuminates two closely matched photodiodes PD1 and PD2, as shown in Figure 1. The input photodiode PD1 can be used to monitor, and therefore stabilize, the light output of the LED. As a result, the on linearity and drift characteristics of the LED can be virtually eliminated. The output photodiode PD2 produces a photocurrent that is linearly related to the light output of the LED. The close matching of the photodiodes and advanced design of the package ensure the high linearity and stable gain characteristics of the optocoupler.

The HCNR200/201 can be used to isolate analog signals in a wide variety of applications that require good stability, linearity, bandwidth and low cost. The HCNR200/201 is very flexible and, by appropriate design of the application circuit, is capable of operating in many different modes, including: unipolar/ bipolar, ac/dc and inverting/ noninverting. The HCNR200/201 is an excellent solution for many analog isolation problems.

In the above circuit set the VR3 to obtain your desired voltage according to the thermocouple output gained .

Source :

1. Complete circuit of Low Cost (8-Channel) Thermocouple Signal Conditioning With Analog Multiplexer and Analog Optocoupler.
2. Datasheet ADG507A
3. Datasheet AD595
4. Datasheet INA126
5. Datasheet HCNR201
6. Thermacouple Singnal Conditioning PCB (Bottom Track).zip
7. Thermacouple Singnal Conditioning PCB (Solder Mask).zip
8. Thermacouple Singnal Conditioning PCB (TOP Legend).zip

The author is not responsible for any risk caused by this circuit. Refer all to the datasheet.

Circuit Cellar November 2010

Circuit Cellar specializes in creative solutions, unique applications and useful design techniques for hands-on designers and developers. Circuit Cellar - is the magazine for computer applications. Click Here to Download