A lot of people dislike the Bosch L-Jetronic fuel injection system fitted to the 411 and 412 in 1971 and the Beetle, Super Beetle, and Bus in 1975. Most of the complaints seem to stem from the fear of the unknown. They don't understand the system and so are afraid of it and rip it off to put some junk carb on their engines, then they wonder why they run like crap. :-)

In reality, the L-Jetronic system is very simple, very reliable, and easy to diagnose. All you need for diagnostic tools is a fuel pressure gauge and a multimeter, and a manual. The Bentely manual does an excellent job of explaining FI diagnostic procedures. Most people blame ignition system problems on the fuel injection and go on a parts-replacing spree, wasting unnecessary money. So it is imperative that before diagnosing the fuel injection system, the ignition system must be in tip-top shape.

This part of the Tech Page endeavors to explain the functions of the various fuel injection parts so that the seeminly mysterious fuel injection system will be revealed for what it is: a bunch of simple parts working together. I will try to have photos here as soon as possible.

Bosch L-Jetronic Fuel Injection.
Air Flow Meter.
Fuel Pump.
Fuel Filter.
Fuel Pressure Regulator.
Fuel Injectors.
Series Resistors.
Electronic Control Unit.
Double Relay.
Cylinder Head Temperature Sensor.
Cold Start Valve.
Thermo-Time Switch.
Auxiliary Air Regulator.
Throttle Switch.
Oxygen Sensor.

For detailed troubleshooting information on your Bosch L-Jetronic system, check out the Bosch FI manual online, which is a scanned in Bosch L-Jetronic manual with great flow-charts for troubleshooting.

If you have any questions, additions, corrections, or comments about the above articles or you just want to say hello, please feel free to send me some e-mail.