Injection Systems

Fuel injection is the introduction of fuel in an internal combustion engine, most commonly automotive engines, by the means of an injector. This article focuses on fuel injection in reciprocating piston and rotary piston engines.

All Diesel (compression-ignition) engines use fuel injection, and many Otto (spark-ignition) engines use fuel injection of one kind or another. Mass-produced Diesel engines for passenger cars (such as the Mercedes-Benz OM 138) became available in the late 1930s and early 1940s, being the first fuel injected engines for passenger car use. In passenger car petrol engines, fuel injection was introduced in the early 1950s, and gradually gained prevalence until it had largely replaced carburetors by the early 1990s.The primary difference between carburetion and fuel injection is that fuel injection atomizes the fuel through a small nozzle under high pressure, while a carburetor relies on suction created by intake air accelerated through a Venturi tube to draw the fuel into the airstream.

The term "fuel injection" is vague and comprises various distinct systems with fundamentally different functional principles. Typically, the only thing in common all fuel injection systems have is the lack of carburetion. There are two main functional principles of mixture formation systems for internal combustion engines: internal mixture formation, and external mixture formation. A fuel injection system that uses external mixture formation is called a manifold injection system; there exist two types of manifold injection systems: multi-point injection (port injection), and single-point injection (throttle-body injection). Internal mixture formation systems can be separated into direct, and indirect injection systems. There exist several different varieties of both direct and indirect injection systems, the most common internal mixture formation fuel injection system is the common-rail injection system, a direct injection system. The term electronic fuel injection refers to any fuel injection system having an engine control unit.

An ideal fuel injection system can precisely provide exactly the right amount of fuel under a all engine operating conditions. This typically means a precise air-fuel-ratio (lambda) control, which allows, for instance: easy engine operation even at low engine temperatures (cold start), good adaptation to a wide range of altitudes and ambient temperatures, exactly governed engine speed (including idle and redline speeds), good fuel efficiency, and only few exhaust emissions (because it allows emissions control devices such as a three-way catalyst to function properly).

In practice an ideal fuel injection system does not exist, but there is a huge variety of different fuel injection systems with certain advantages and disdvantages. Most of these systems were rendered obsolete by the common-rail direct injection system that is nowadays (2020) used in many passenger cars. Common-rail injection allows petrol direct injection, and is even better suited for diesel engine fuel direct injection. However, common-rail injection is a relatively complex system, which is why in some passenger cars that do not use diesel engines, a multi-point manifold injection system is used instead.

When designing a fuel injection system, a variety of factors has to be taken into consideration, including:

System cost
Engine performance and vehicle driveability (ease of starting, smooth running, etc.)
exhaust emissions
Diagnostic provisions and ease of service
Fuel efficiency
Reliability
Ability to run on various fuels

All fuel injection systems comprise three basic components: they have at least one fuel injector (sometimes called an injection valve), a device that creates sufficient injection pressure, and a device that meters the correct amount of fuel. These three basic components can either be separate devices (fuel injector(s), fuel distributor, fuel pump), partially combined devices (injection valve and an injection pump), or completely combined devices (unit injector). Early mechanical injection systems (except air-blast injection) typically used injection valves (with needle nozzles) in combination with a relatively sophisticated helix-controlled injection pump that both metered the fuel, and created the injection pressure. They were well-suited for intermittently injecting multi-point injection systems as well as all sorts of conventional direct injection systems, and chamber-injected systems. Advancements in the field of microelectronics allowed injection system manufacturers to significantly improve the accuracy of the fuel metering device. In modern engines, the fuel metering and injection valve actuation is usually done by the engine control unit. Therefore, the fuel injection pump does not have to meter the fuel or actuate the injection valves; it only needs to provide injection pressure. These modern systems are used in multi-point-injected engines, and common-rail-injected engines. Unit injection systems have made it into series production in the past, but proved to be inferior to common-rail injection.

Multi-point injection

Multi-point injection injects fuel into the intake ports just upstream of each cylinder's intake valve, rather than at a central point within an intake manifold. Typically, multi-point injected systems use multiple fuel injectors, but some systems such as the GM central port injection use tubes with poppet valves fed by a central injector instead of multiple injectors.

Injection schemes

Manifold injected engines can use several injection schemes: continuous, and intermittent (simultaneous, batched, sequential, and cylinder-individual).

In a continuous injection system, fuel flows at all times from the fuel injectors, but at a variable flow rate. The most common automotive continuous injection system is the Bosch K-Jetronic, introduced in 1974, and used until the mid-1990s by various car manufacturers. Intermittent injection systems can be sequential, in which injection is timed to coincide with each cylinder's intake stroke; batched, in which fuel is injected to the cylinders in groups, without precise synchronization to any particular cylinder's intake stroke; simultaneous, in which fuel is injected at the same time to all the cylinders; or cylinder-individual, in which the engine control unit can adjust the injection for each cylinder individually.

Internal mixture formation
In an engine with an internal mixture formation system, air and fuel are mixed only inside the combustion chamber. Therefore, only air is sucked into the engine during the intake stroke. The injection scheme is always intermittent (either sequential or cylinder-individual). There are two different types of internal mixture formation systems: indirect injection, and direct injection.
Indirect injection
Air-cell chamber injection – the fuel injector (on the right) injects the fuel through the main combustion chamber into the air-cell chamber on the left. This is a special type of indirect injection and was very common in early American diesel engines.
Main article: Indirect injection
This article describes indirect injection as an internal mixture formation system (typical of Akroyd and Diesel engines); for the external mixture formation system that is sometimes called indirect injection (typical of Otto and Wankel engines), this article uses the term manifold injection.
In an indirect injected engine, there are two combustion chambers: a main combustion chamber, and a pre-chamber, that is connected to the main one. The fuel is injected only into the pre-chamber (where it begins to combust), and not directly into the main combustion chamber. Therefore, this principle is called indirect injection. There exist several slightly different indirect injection systems that have similar characteristics. All Akroyd (hot-bulb) engines, and some Diesel (compression ignition) engines use indirect injection.
Direct injection
Direct injection means that an engine only has a single combustion chamber, and that the fuel is injected directly into this chamber.[16] This can be done either with a blast of air (air-blast injection), or hydraulically. The latter method is far more common in automotive engines. Typically, hydraulic direct injection systems spray the fuel into the air inside the cylinder or combustion chamber, but some systems spray the fuel against the combustion chamber walls (M-System). Hydraulic direct injection can be achieved with a conventional, helix-controlled injection pump, unit injectors, or a sophisticated common-rail injection system. The latter is the most common system in modern automotive engines. Direct injection is well-suited for a huge variety of fuels, including petrol (see petrol direct injection), and diesel fuel.
Main article: common-rail injection
In a common rail system, the fuel from the fuel tank is supplied to the common header (called the accumulator). This fuel is then sent through tubing to the injectors, which inject it into the combustion chamber. The header has a high pressure relief valve to maintain the pressure in the header and return the excess fuel to the fuel tank. The fuel is sprayed with the help of a nozzle that is opened and closed with a needle valve, operated with a solenoid. When the solenoid is not activated, the spring forces the needle valve into the nozzle passage and prevents the injection of fuel into the cylinder. The solenoid lifts the needle valve from the valve seat, and fuel under pressure is sent in the engine cylinder.Third-generation common rail diesels use piezoelectric injectors for increased precision, with fuel pressures up to 300 MPa or 44,000 lbf/in2 (3000 Bar or 3.033 Bar).

History and development

1870s – 1920s: early systems

Air-blast injection system for a 1898 diesel engine

In 1872, George Bailey Brayton obtained a patent on an internal combustion engine that used a pneumatic fuel injection system, also invented by Brayton: the air-blast injection. In 1894, Rudolf Diesel copied Brayton's air-blast injection system for the diesel engine, but also improved it. Most notably, Diesel increased the air-blast pressure from 4–5 kp/cm2 (390–490 kPa) to 65 kp/cm2 (6,400 kPa).

The first manifold injection system was designed by Johannes Spiel at Hallesche Maschinenfabrik in 1884. In the early 1890s, Herbert Akroyd Stuart developed an indirect fuel injection system using a 'jerk pump' to meter out fuel oil at high pressure to an injector. This system was used on the Akroyd engine and was adapted and improved by Bosch and Clessie Cummins for use on diesel engines.

A manifold-injected Antoinette 8V aviation engine, mounted in a preserved Antoinette VII monoplane aircraft.

In 1898, Deutz AG started series production of stationary four-stroke Otto engines with manifold injection. Eight years later, Grade equipped their two-stroke engines with manifold injection, and both Antoinette 8V and Wright aircraft engines were fitted with manifold injection as well. The first engine with petrol direct injection was a two-stroke aircraft engine designed by Otto Mader in 1916.

Another early use of petrol direct injection was on the Hesselman engine invented by Swedish engineer Jonas Hesselman in 1925. Hesselman engines use the stratified charge principle; fuel is injected towards the end of the compression stroke, then ignited with a spark plug. They can run on a huge variety of fuels.

The invention of the pre-combustion chamber injection by Prosper l'Orange helped Diesel engine manufacturers to overcome the problems of air-blast injection, and allowed designing small engines for automotive use from the 1920s onwards. In 1924, MAN presented the first direct-injected Diesel engine for

1930s – 1950s: first mass-produced petrol direct injection

Direct petrol injection was used in notable World War II aero-engines such as the Junkers Jumo 210, the Daimler-Benz DB 601, the BMW 801, the Shvetsov ASh-82FN (M-82FN). German direct injection petrol engines used injection systems developed by Bosch, Deckel, Junkers and l'Orange from their diesel injection systems.[Later versions of the Rolls-Royce Merlin and Wright R-3350 used single point injection, at the time called "Pressure Carburettor". Due to the wartime relationship between Germany and Japan, Mitsubishi also had two radial aircraft engines using petrol direct injection, the Mitsubishi Kinsei and the Mitsubishi Kasei.

The first automotive direct injection system used to run on petrol was developed by Bosch, and was introduced by Goliath for their Goliath GP700, and Gutbrod for their Superior in 1952. This was basically a specially lubricated high-pressure diesel direct-injection pump of the type that is governed by the vacuum behind an intake throttle valve. The 1954 Mercedes-Benz W196 Formula 1 racing car engine used Bosch direct injection derived from wartime aircraft engines. Following this racetrack success, the 1955 Mercedes-Benz 300SL, became the first passenger car with a four-stroke Otto engine that used direct injection.Later, more mainstream applications of fuel injection favored the less-expensive manifold injection.

1950s – 1980s: series production manifold injection systems

A 1959 Corvette small-block 4.6 litre V8 with Rochester manifold fuel injection

Unpowered, continuously injecting multi-point injection Bosch K-Jetronic

Throughout the 1950s, several manufacturers introduced their manifold injection systems for Otto engines, including General Motors' Rochester Products Division, Bosch, and Lucas Industries. During the 1960s, additional manifold injection systems such as the Hilborn, Kugelfischer, and SPICA systems were introduced.

The first commercial electronicially controlled manifold injection system was the Electrojector developed by Bendix and was offered by American Motors Corporation (AMC) in 1957. Initial problems with the Electrojector meant only pre-production cars had it installed so very few cars were sold and none were made available to the public.The EFI system in the Rambler worked well in warm weather, but was difficult to start in cooler temperatures.

Chrysler offered Electrojector on the 1958 Chrysler 300D, DeSoto Adventurer, Dodge D-500, and Plymouth Fury, arguably the first series-production cars equipped with an EFI system. The Electrojector patents were subsequently sold to Bosch, who developed the Electrojector into the Bosch D-Jetronic. The D in D-Jetronic stands for Druckfühlergesteuert, German for "pressure-sensor controlled"). The D-Jetronic was first used on the VW 1600TL/E in 1967. This was a speed/density system, using engine speed and intake manifold air density to calculate "air mass" flow rate and thus fuel requirements.

Bosch superseded the D-Jetronic system with the K-Jetronic and L-Jetronic systems for 1974, though some cars (such as the Volvo 164) continued using D-Jetronic for the following several years. The L-Jetronic uses a mechanical airflow meter (L for Luft, German for "air") that produces a signal that is proportional to volume flow rate. This approach required additional sensors to measure the atmospheric pressure and temperature, to calculate mass flow rate. L-Jetronic was widely adopted on European cars of that period, and a few Japanese models a short time later.

1979 – 1990s

The first digital engine management system (engine control unit) was the Bosch Motronic introduced in 1979. In 1980, Motorola (now NXP Semiconductors) introduced their digital ECU EEC-III. The EEC-III a single-point injection system.

Manifold injection was phased in through the latter 1970s and 80s at an accelerating rate, with the German, French, and U.S. markets leading and the UK and Commonwealth markets lagging somewhat. Since the early 1990s, almost all petrol passenger cars sold in first world markets are equipped with electronic manifold injection. The carburetor remains in use in developing countries where vehicle emissions are unregulated and diagnostic and repair infrastructure is sparse. Fuel injection systems are gradually replacing carburetors in these nations too as they adopt emission regulations conceptually similar to those in force in Europe, Japan, Australia, and North America.

Since 1990

In 1995, Mitsubishi presented the first common-rail petrol direct injection system for passenger cars. It was introduced in 1997. Subsequently, common-rail direct injection was also introduced in passenger car diesel engines, with the Fiat 1.9 JTD being the first mass market engine.In the early 2000s, several car manufacturers attempted to use stratified charge concepts in their direct injection petrol engines to reduce fuel consumption. However, the fuel savings proved to be almost unnoticeable and disproportional to the increased complexity of the exhaust gas treatment systems. Therefore, almost all car manufacturers have switched to a conventional homogneneous mixture in their direct injected petrol engines since the mid 2010s. In the early 2020s, some car manufacturers have still been using manifold injection, especially in economy cars, but also some high performance cars. Ever since 1997, car manufacturers have been using common-rail direct injection for their diesel engines. Only Volkswagen used the Pumpe-Düse system throughout the early 2000s, but they have also been using common-rail direct injection since 2010.

Jetronic

Jetronic is a trade name of a manifold injection technology for automotive petrol engines, developed and marketed by Robert Bosch GmbH from the 1960s onwards. Bosch licensed the concept to many automobile manufacturers. There are several variations of the technology offering technological development and refinement.

D-Jetronic (1967–1979)

Analogue fuel injection, 'D' is from German: "Druck" meaning pressure. Inlet manifold depression (vacuum) is measured using a pressure sensor located in, or connected to the intake manifold, in order to calculate the duration of fuel injection pulses. Originally, this system was called Jetronic, but the name D-Jetronic was later created as a retronym to distinguish it from subsequent Jetronic iterations.

D-Jetronic was essentially a further refinement of the Electrojector fuel delivery system developed by the Bendix Corporation in the late 1950s. Rather than choosing to eradicate the various reliability issues with the Electrojector system, Bendix instead licensed the design to Bosch. With the role of the Bendix system being largely forgotten D-Jetronic became known as the first widely successful precursor of modern electronic common rail systems; it had constant pressure fuel delivery to the injectors and pulsed injections, albeit grouped (2 groups of injectors pulsed together) rather than sequential (individual injector pulses) as on later systems.

As in the Electrojector system, D-Jetronic used analogue circuitry, with no microprocessor nor digital logic, the ECU used about 25 transistors to perform all of the processing. Two important factors that led to the ultimate failure of the Electrojector system: the use of paper-wrapped capacitors unsuited to heat-cycling and amplitude modulation (AM radio) signals to control the injectors were superseded. The still present lack of processing power and the unavailability of solid-state sensors meant that the vacuum sensor was a rather expensive precision instrument, rather like a barometer, with brass bellows inside to measure the manifold pressure.

Although conceptually similar to most later systems with individual electrically controlled injectors per cylinder, and pulse-width modulated fuel delivery, the fuel pressure was not modulated by manifold pressure, and the injectors were fired only once per 2 revolutions on the engine (with half of the injectors being fired each revolution).

The system was last used (with a Lucas designed timing mechanism and Lucas labels super-imposed on some components) on the Jaguar V12 engine (XJ12 and XJ-S) from 1975 until 1979.

K-Jetronic (1973–1994)

Mechanical fuel injection, 'K' stands for German: "Kontinuierlich", meaning continuous. Commonly called 'Continuous Injection System (CIS) in the USA. K-Jetronic is different from pulsed injection systems in that the fuel flows continuously from all injectors, while the fuel pump pressurises the fuel up to approximately 5 bar (73.5 psi). The volume of air taken in by the engine is measured to determine the amount of fuel to inject. This system has no lambda loop or lambda control. K-Jetronic debuted in the 1973.5 Porsche 911T in January 1973, and was later installed into a number of Porsche, Volkswagen, Audi, BMW, Mercedes-Benz, Rolls-Royce, Bentley, Lotus, Ferrari, Peugeot, Nissan, Renault, Volvo, Saab, TVR and Ford automobiles. The final car to use K-Jetronic was the 1994 Porsche 911 Turbo 3.6.

Fuel is pumped from the tank to a large control valve called a fuel distributor, which divides the single fuel supply line from the tank into smaller lines, one for each injector. The fuel distributor is mounted atop a control vane through which all intake air must pass, and the system works by varying fuel volume supplied to the injectors based on the angle of a moving vane in the air flow meter, which in turn is determined by the volume of air passing the vane, and by the control pressure. The control pressure is regulated with a mechanical device called the control pressure regulator (CPR) or the warm-up regulator (WUR). Depending on the model, the CPR may be used to compensate for altitude, full load, and/or a cold engine. The injectors are simple spring-loaded check valves with nozzles; once fuel system pressure becomes high enough to overcome the counterspring, the injectors begin spraying.

Motronic

Motronic is the trade name given to a range of digital engine control units developed by Robert Bosch GmbH (commonly known as Bosch) which combined control of fuel injection and ignition in a single unit. By controlling both major systems in a single unit, many aspects of the engine's characteristics (such as power, fuel economy, drivability, and emissions) can be improved.

Motronic 1.x

1.0

Often known as "Motronic basic", Motronic ML1.x was one of the first digital engine-management systems developed by Bosch. These early Motronic systems integrated the spark timing element with then-existing Jetronic fuel injection technology. It was originally developed and first used in the BMW 7 Series, before being implemented on several Volvo and Porsche engines throughout the 1980s.

The components of the Motronic ML1.x systems for the most part remained unchanged during production, although there are some differences in certain situations. The engine control module (ECM) receives information regarding engine speed, crankshaft angle, coolant temperature and throttle position. An air flow meter also measures the volume of air entering the induction system.

If the engine is naturally aspirated, an air temperature sensor is located in the air flow meter to work out the air mass. However, if the engine is turbocharged, an additional charge air temperature sensor is used to monitor the temperature of the inducted air after it has passed through the turbocharger and intercooler, in order to accurately and dynamically calculate the overall air mass.

Main system characteristics

Fuel delivery, ignition timing, and dwell angle incorporated into the same control unit.
Crank position and engine speed is determined by a pair of sensors reading from the flywheel.
Separate constant idle speed system monitors and regulates base idle speed settings.
5th injector is used to provide extra fuel enrichment during different cold-start conditions. (in some configurations)
Depending on application and version, an oxygen sensor may be fitted (the system was originally designed for leaded fuel).

1.1

Motronic 1.1 was used by BMW from 1987 on motors such as the M20.

The systems have the option for a lambda sensor, enabling their use with catalytic converter-equipped vehicles. This feedback system allows the system to analyse exhaust emissions so that fuel and spark can be continually optimised to minimise emissions. Also present is adaptive circuitry, which adjusts for changes in an engine's characteristics over time. Some PSA engines also include a knock sensor for ignition timing adjustment, perhaps this was achieved using an external Knock Control Regulator.

The Motronic units have 2 injection outputs, and the injectors are arranged in 2 "banks" which fire once every two engine revolutions. In an example 4-cylinder engine, one output controls the injectors for cylinders 1 and 3, and the other controls 2 and 4. The system uses a "cylinder ID" sensor mounted to the camshaft to detect which cylinders are approaching the top of their stroke, therefore which injector bank should be fired. During start-up (below 600 rpm), or if there is no signal from the cylinder ID sensor, all injectors are fired simultaneously once per engine revolution.[5] In BMW vehicles, this Motronic version did not have a cylinder ID and as a result, both banks of injectors fired at once.

1.2

Motronic 1.2 is the same as 1.1, but uses a hot-film MAF in place of the flapper-door style AFM. This version was used by BMW on the S38B36 engine in the E34 M5 and on the M70B50 engine in the 750il from 1988 until 1990.

1.3

Motronic 1.1 was superseded in 1988 by the Motronic 1.3 system that was also used by PSA on some XU9J-series engines (which previously used Motronic 4.1). and by BMW.

The Motronic 1.1 and 1.3 systems are largely similar, the main improvement being the increased diagnostic capabilities of Motronic 1.3. The 1.3 ECM can store many more detailed fault codes than 1.1, and has a permanent 12-volt feed from the vehicle's battery which allows it to log intermittent faults in memory across several trips. Motronic 1.1 can only advise of a few currently-occurring faults.

1.5

This system was used on some of General Motors engines (C20NE, 20NE, C20SE, 20SE, 20SEH, 20SER, C20NEF, C20NEJ, C24NE, C26NE, C30LE, C30NE, C30SE, C30SEJ, C30XEI...). The system is very reliable and problems encountered are usually caused by poor contact at the associated plug/socket combinations that link the various system sensors to the Electronic Control Unit (ECU). Predecessor of the ME Motronic. Also used in the Opel engines C16SEI

1.5.2

Was used since 1991 in the Opel Astra F with C20NE engine. Major change was the use of a MAF instead of AFM in the Motronic 1.5.

1.5.4

Was used since 1994 in the Opel Omega B with X20SE engine. (Modified successor of C20NE engine) Major change to the Motronic 1.5.2 was the use of DIS ignition system, knock sensor and EGR valve. Was also used in the Opel engine X22XE.

1.7

The key feature of Motronic 1.7 is the elimination of an ignition distributor, where instead each cylinder has its own electronically triggered ignition coil. Motronic 1.7 family has versions 1.7, 1.7.2, 1.7.3, all of them used on M42/M43 engines in BMW 3 Series (E36) up to 1998 and BMW 5 Series (E34) up to 1995.The BMW M70 12 cylinder had the Motronic M1.7 and two distributors.

1.8

This system was used by Volvo on some Volvo 960 cars.

Motronic 2.x

2.1

The ML 2.1 system integrates an advanced engine management with 2 knock sensors, provision for adaptive fuel & timing adjustment, purge canister control, precision sequential fuel control and diagnostics (pre OBD-1). Fuel enrichment during cold-start is achieved by altering the timing of the main injectors based on engine temperature. The idle speed is also fully controlled by the digital Motronic unit, including fast-idle during warm-up. Updated variants ML 2.10.1 thru 2.5 add MAF Mass Air Flow sensor logic and direct fire ignition coils per cylinder. Motronic 2.1 is used in the Porsche 4 cyl 16V 944S/S2/968 and the 6 cyl Boxer Carrera 964 & 993, Opel/Vauxhall, FIAT & Alfa Romeo engines.

2.3/2.3.2

The M2.3.2 system was made for Audi's turbo 20V 5 cylinder engines mainly but a variant was also used on the Audi 32V 3.6L V8 and a few Audi 32V 4.2 V8 engines. The turbo 5 cylinder version was the first time knock and boost control had been introduced in one ECU though the ECU was really two computers in one package. One side of the ECU controlled the timing and fueling while the other side controlled the boost and knock control. Each side has its own Siemens SAB80C535 process and its own eprom for storing operating data. What made this ECU strange was the use of two crank sensors and one cam sensor. The ECU used one crank sensor to count the teeth on the starter ring for its RPM signal and the other read a pin on the back of the flywheel for TDC reference. This ECU was first seen when the 20V turbo 5 cylinder engine (RR Code) was installed into the Audi Quattro. It was then used in the Audi 200 20V turbo until 1991 when the Audi S4 was introduced and the ECU received several upgrades, including migration from a distributor based ignition to coil on plug sequential ignition and an added overboost function. This ECU ended in 1997 when the last Audi S6 rolled off the assembly line. This ECU was also used in the legendary Audi RS2 Avant.

The V8 version of the ECU was only single processor based while retaining all the same features of the turbo 5 cylinder ECU less the boost control. The 3.6 V8 version had a distributor based ignition system and was upgraded around the same time to coil on plug as its 20V turbo counterpart in 1992–1993.

2.5

Was introduced in 1988 in the Opel Kadett E GSi 16V C20XE engine. Sequential fuel injection and knock control.

2.7

Late '80s and early '90s, various Ferrari. Some Opel / Vauxhall (C20LET engine).

2.8

Successor of the Motronic 2.5. Was used from 1992 at Opel C20XE engine. Major change was the introduction of DIS ignition. Was also at Opel V6 engine C25XE used. Modified as M2.8.1, M2.8.3 at Opel V6 engine X25XE and X30XE.

Motronic 3.x

3.1

Compared with ML1.3, this system adds knock sensor control, purge canister control and start-up diagnostics. Motronic 3.1 is used in non-VANOS BMW M50B25 engines.

3.3.1

Motronic 3.3.1 is used in BMW M50B25 engines with VANOS.

3.7

Motronic 3.7 is used in the Alfa Romeo V6 engine in the later 12 valve 3.0L variants, replacing the L-Jetronic.

3.7.1

Motronic 3.7.1 is used in the Alfa Romeo V6 engine in the 24 valve variants.

Motronic 4.X

40.0

40.1

4.1

The Motronic 4.1 system was used on Opel / Vauxhall eight-valve engines from 1987 to 1990, Alfa Romeo and some PSA Peugeot Citroën XU9J-series engines.

Fuel enrichment during cold-start is achieved by altering the timing of the main injectors based on engine temperature, no "cold start" injector is required. The idle speed is also fully controlled by the Motronic unit, including fast-idle during warm-up (therefore no thermo-time switch is required).

The 4.1 system did not include provision for a knock sensor for timing adjustment. The ignition timing and fuel map could be altered to take account of fuels with different octane ratings by connecting a calibrated resistor (taking the form of an "octane coding plug" in the vehicle's wiring loom) to one of the ECU pins, the resistance depending on the octane adjustment required. With no resistor attached the system would default to 98 octane.

There is a single output for the injectors, resulting in all injectors firing simultaneously. The injectors are opened once for every revolution of the engine, injecting half the required fuel each time.

Motronic ML4.1 was used in the Opel engines: 20NE, 20SE, 20SEH, 20SER, C20NE, C30LE, C30NE.

4.3

The Motronic 4.3 was used by Volvo for their five-cylinder turbocharged 850 models from 1993 until 1996.

It was introduced with the launch of the 850 Turbo (also called the 850 T-5 and 850 T-5 Turbo) in October 1993 for model year 1994. Features included OBD I diagnostics, dual knock sensors and a lot more. For the 1996 model year OBD II diagnostics were introduced on some cars while M4.3 was beginning to be phased out. The last M4.3 equipped cars were made for model year 1997.

4.4

The Motronic 4.4 was used by Volvo from 1996 until 1998.

The M4.4 was based on its predecessor and featured only a small number of improvements. Memory capacity was doubled and a few new functions were introduced such as immobilizer compatibility. OBD II was standard on all cars fitted with this system albeit the necessary protocols were not integrated for all markets. The system was used for the five- and six-cylinder modular engined cars and was used on turbocharged and naturally aspirated models. Introduced in 1996 for 1997 model year it was first installed on some of the last 850 models like the 2.5 20V and AWD. A coil on plug variant existed for the six cylinder Volvo 960/S90/V90. After the 850 was replaced by the Volvo V70, Volvo S70 and Volvo C70 the system was used until the end of model year 1998.

Motronic 5.x

5.2

Motronic 5.2 was used in the BMW M44B19 engine. Compared to 1.7, Motronic 5.2 has OBD-II capability and uses a hot-wire MAF sensor in place of the flapper-door AFM

5.2.1

Motronic 5.2.1 was used in Land Rover Discovery Series II and P38 Range Rovers that were built starting with late 1999. It was only used in cars equipped with V8 gasoline engines. This variant of the engine management system was adapted for off-road use. Unlike the Motronic system in BMW sedans, that uses a chassis accelerometer to differentiate between misfires and rough road, the Land Rover version used signal from ABS control unit to detect rough road conditions. This version of the system was integrated with body control module and anti-theft system.

Digifant engine management system

The Digifant engine management system is an electronic engine control unit (ECU), which monitors and controls the fuel injection and ignition systems in petrol engines, designed by Volkswagen Group, in cooperation with Robert Bosch GmbH.

Digifant is the outgrowth of the Digijet fuel injection system first used on water-cooled Volkswagen A2 platform-based model

History

Digifant was introduced in 1986 on the 2.1 litre Volkswagen Type 2 (T3) (Vanagon in the US) engine. This system combined digital fuel control as used in the earlier Digi-Jet systems with a new digital ignition system. The combination of fuel injection control and ignition control is the reason for the name "Digifant II" on the first version produced. Digifant as used in Volkswagen Golf and Volkswagen Jetta models simplified several functions, and added knock sensor control to the ignition system. Other versions of Digifant appeared on the Volkswagen Fox, Corrado, Volkswagen Transporter (T4) (known as the Eurovan in North America), as well as 1993 and later production versions of the rear-engined Volkswagen Beetle, sold only in Mexico. Lower-power versions (without a knock sensor), supercharged, and 16-valve variants were produced. Nearly exclusive to the European market, Volkswagen AG subsidiary Audi AG also used the Digifant system, namely in its 2.0 E variants of the Audi 80 and Audi 100.

Digifant is an engine management system designed originally to take advantage of the first generation of newly developed digital signal processing circuits. Production changes and updates were made to keep the system current with the changing California and federal emissions requirements. Updates were also made to allow integration of other vehicle systems into the scope of engine operation.

Changes in circuit technology, design and processing speed along with evolving emissions standards, resulted in the development of new engine management systems. These new system incorporated adaptive learning fuzzy logic, enhanced and expanded diagnostics, and the ability to meet total vehicle emissions standards.

Features

Fuel injection control is digitally electronic. It is based on the measurement engine load (this signal is provided by the Air Flow Sensor), and on engine speed (signal provided by the Hall sender in the distributor). These primary signals are compared to a 'map', or table of values, stored in the Engine Control Module (ECM) memory.

The amount of fuel delivered is controlled by the duration of actuation of the fuel injector(s). This value is taken from a programme in the ECM that has 16 points for load and 16 points for speed. These 256 primary values are then modified by coolant temperature, intake air temperature, oxygen content of the exhaust, car battery voltage and throttle position - to provide 65,000 possible injector duration points.

Digifant is unlike the earlier CIS and CIS-E fuel injection systems that it replaced, in that fuel injectors are mounted on a common fuel rail. CIS fuel injection systems used mechanical fuel injectors. The fuel injectors are wired in parallel, and are supplied with Constant System Voltage. The ECM switches the earth/ground on and off to control duration. All injectors operate at the same time (simultaneously, rather than sequentially) each crankshaft revolution; two complete revolutions being needed for each cylinder to receive the correct amount of fuel for each combustion cycle.

Ignition system control is also digital electronic. The sensors that supply the engine load and engine speed signals for injector duration provide information about the basic ignition timing point. The signal sent to the Hall control unit is derived from a programme in the ECM that is similar to the injector duration programme.

Engine knock control is used to allow the ignition timing to continually approach the point of detonation. This is the point where the engine will produce the most motive power, as well as the highest efficiency.

Additional functions of the ECM include operation of the fuel pump by closing the Ground for the fuel pump relay, and control of idle speed by a throttle plate bypass valve. The Idle Air Control Valve (IACV) (previously known as an Idle Air Stabiliser Valve - IASV), receives a changing milliamp signal that varies the strength of an electromagnet pulling open the bypass valve.

Idle speed stabilisation is enhanced by a process known as Idle Speed Control (ISC). This function (previously known as Digital Idle Stabilization), allows the ECM to modify ignition timing at idle to further improve idle quality.

Digifant II inputs/outputs

The 25 pin electronic control unit used in the Golf and Jetta receives inputs from the following sources:

Hall sender unit (provides engine speed signal)
Air Flow Sensor (provides engine load information)
Coolant temperature sensor
Intake Air Temperature sensor
Knock sensor

Additional signals used as inputs are:

Air conditioner (compressor on)
Car battery voltage
Starter motor signal

Digifant system inputs/outputs

The Anti-lock Braking System (ABS), three-speed automatic transmission, and vehicle speed sensor are not linked to this system.

Outputs controlling engine operation include signals to the following:

Fuel injectors
Idle Air Control Valve
Hall control unit
Fuel pump relay
Oxygen sensor heater

Additional systems

The evaporative emission system is controlled by a vacuum-operated mechanical carbon canister control valve. Fuel pressure is maintained by a vacuum operated mechanical fuel pressure regulator on the fuel injector rail assembly. Inputs and outputs are shown in the following illustration. Digifant II as used on Golf and Jetta vehicles provides the basis for this chart.

North America variants

In North America, Volkswagen released two other versions of the Digifant fuel injection system (in addition to standard Digifant II described above).

A limited number of 1987-1990 California Golf and Jetta models are equipped with Digifant II that features an on-board diagnostics system (OBD). These vehicles have 'blink code' capacity to store up to five Diagnostic Trouble Codes (DTCs). Diagnostic troubleshooting is done by pressing the Check Engine switch on the dashboard. This system can also have carbon monoxide (CO), ignition timing and idle speed adjusted to baseline values.

In 1991, California Golf, Jetta, Fox, Cabriolet and Corrado vehicles were equipped with expanded OBD capabilities. This version was renamed "Digifant I". These later Digifant versions have 38-pin ECMs with Rapid Data Transfer and permanent DTC memory. All Eurovans with Digifant also have rapid data transfer and permanent DTC memory. These systems use a throttle plate potentiometer to track throttle plate position in place of the idle and full throttle switches used on earlier systems.

Another characteristic of Digifant II equipped vehicles in California is a switch mount on the dashboard which has a "Check Engine" symbol. Digifant I models in California feature a Check Engine light, with the display of codes done by a special Volkswagen tool under the shift boot, or by a jumper and an LED by the home mechanic.

Digifant Reliability

Vehicles using engines equipped with Digifant fuel injection typically operated both efficiently and smoothly when new but suffered from a number of issues as the car aged, even by a few months. Digifant sensors & other components, especially the ECU itself, were remarkably sensitive to poor electrical grounding. Without a reliable ground signal to reference, the system was vulnerable to errors and malfunction. In the 1980s and 1990s many Volkswagen / Audi designs did not incorporate sufficient engine compartment grounding, and when the car's engine compartment became soiled with dirt, oil & road salts from several months / years of use, the fuel injection system would fail in often inexplicable ways. Backfiring, stalls & other poor running were all too common. Later versions were improved by providing multiple grounding paths, but the early Digifant systems suffered poor service reputations.

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Most of driveability issues can be traced back to a few issues:

Bad ECM earth/ground
Bad o2/lambda sensor earth/ground
Faulty Engine Coolant Temperature sensor (ECT)

The engine coolant temperature sensor is located in the coolant flange,(under the distributor on the Polo Fox Coupe) on the front of the cylinder head (on transverse-engine vehicles). The bad earth/ground can be traced to an essential ground strap on the front upper transmission bolt. Without this, the ECU tends to earth/ground elsewhere, causing a specific trace to burn out on the circuit board and killing the ECU. This causes the injectors to stay open constantly, flooding the engine.

1990 Jetta GL with Digifant engine management

Common issues that indicate a failed engine coolant temperature sensor are:

Vehicle idles poorly
Engine sputters, might stall
Higher than normal fuel consumption

The part number for this sensor is '025 906 041 A' (always check with your Volkswagen dealer for the most updated part number). The resistance of this unit is approximately 3.2 Kohm at 10 degrees C. If it measures open circuit this will explain erratic idle and throttle speeds especially when the engine is cold.

When replacing this sensor, it is important to also replace the clip that holds it in position ('032 121 142') and the O-ring ('N 903 168 02').

Once the new sensor has been installed, start the engine and disconnect the blue coolant temperature sensor. Rev the engine through 3,000 rpm three times, each time allowing the throttle to close completely. This clears the Digifant ECM fault memory.