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Alfa 33 Fuel Injection

This section is just intended for information. Please be careful when playing with any fuel injection system as there are some delicate and expensive components that are very easy to damage with cack handed use of a multimeter. From a safety point of view you need to watch out for the high voltages present in the ignition system and the high fuel preasure used which enables fuel to spread over a large area as an explosive mix if a leak develops.

I am not a fuel injection expert, and I expect I have made some mistakes in this. I am just trying to turn what I have written down into some coherant notes which I, and hopefully you, can understand. To add to the fun, some information is taken from documents in French and Dutch, and my French is attrocious and my Dutch non existant. If you find anything wrong please mail me, but sorry there are no prizes.

With a great piece of standardisation, Alfa used 5 different fuel injection systems on the 33 with extra minor variants for versions with catalytic converters and with 4wd. This doesn't include the stuff fitted to turbo diesel versions which I have no interest in and, as they rarely seem to get beyond Italy in any numbers, I am unlikely to see.

The early series 2 fuel injected 33's were fitted with a Bosch Bosch LE3 Jetronic system. These cars were only sold in markets with fairly strict emisions rules, such as Australia. Although similar to most Bosch systems fitted to other 33's, there are differences. There is a manual supplement for this model which can be downloaded from the net from James Barretts 33 Page or from Arda's web page.

With the advent of the series 3 Alfa decided to use a wider variety of systems. For the 16 valve models a Bosch ML4.1 system was used. This multi point fuel injection system used an air flow meter and individual throttle bodies (made by Dellorto), and could be fitted with a catalytic converter. This system seems to have the greatest capacity for making a mess of itself, and there is a small patch lead available from Alfa which fits between the air flow meter and the wiring loom to compensate for some problems (apparently a build up of static electricity in the AFM causes false readings on a constant throttle opening........but that sounds like marketing rubbish to me).

For the normal 1.5IE and 1.7IE models a Bosch LE3 Jetronic system was used. This system again used an air flow meter, but with a single throttle body and a seperate ignition system. This model is just about impossible to chip, but is available in versions with and without a cat. If you want to adjust the timing (which is where most of the power gains are to be found with chipping) you will need to do some playing with the distributer

Later on the 1.5IE and 1.7IE moved over to using the Bosch MP3.1 system, with a single individual throttle body. The system does not use an air flow meter or an air mass meter. Instead a MAP (manifold absolute preasure) sensor is used, built into the ECU with a pipe to supply the air. On the intake there is an air temperature sensor. This system, as far as I know, was always fitted to cars with a lambda probe and a catalytic converter. The ECU is identical between the two engine sizes with just a jumper to switch between them. I suspect this jumper just controls the rev limiter, but I don't know to be honest. Perhaps this systems best features are the ability to learn from the lambda sensor (although this information is forgotten when the battery is disconnected and this can result in poor running while the system relearns its settings) and the ability to self diagnose problems and present them as a series of flash codes. Views of the engine bay of a 1.7IE fitted with the Bosch MP3.2 system are to be found here.

For the 1351cc injected cars (1.3 or 1.4, depending on the market), Alfa used a multi point Weber IAW system, again using a single throttle body. This system uses a very similar manifold to the Bosch MP3.1, but it has a seperate MAP sensor and a slightly different arrangement for the idle stabilisation valve.