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The world of automotive fuel delivery systems is a fascinating realm of engineering precision, and few technologies capture this essence quite like the Continuous Injection System (CIS) developed by Bosch. Particularly in Audi vehicles of the 1970s and 1980s, CIS represented a revolutionary approach to fuel management that bridged the gap between traditional carburetors and modern electronic fuel injection.
Understanding CIS: The Mechanical Marvel of Fuel Delivery
At its core, CIS (Continuous Injection System) is an ingenious electro-mechanical fuel injection technology that fundamentally changed how fuel was delivered to engine cylinders. Unlike traditional fuel systems, CIS does something remarkable: it continuously sprays fuel during the entire combustion cycle. This approach offered several significant advantages:
- Precise Fuel Metering: The system uses an air flow sensor that directly controls fuel distribution
- Improved Emissions Control: More consistent fuel delivery meant better combustion efficiency
- Enhanced Fuel Economy: More accurate fuel-air mixture compared to carburetors
How CIS Works in Audi Vehicles
The magic of CIS lies in its mechanical complexity. When an Audi equipped with CIS accelerates, a large flapper valve upstream of the throttle body rises proportionally to the air intake. This movement is mechanically linked to a fuel distributor piston, which adjusts fuel pressure sent to the injectors.
In early Audi models like the 1973-1983 911 series, CIS was an open-loop system with no emissions feedback. Later versions, particularly in Audi's turbocharged models, incorporated a Lambda closed-loop circuit with an oxygen sensor to fine-tune the fuel mixture even further.
The Challenges of CIS Technology
Despite its innovative design, CIS was not without drawbacks. Automotive enthusiasts often critique the system for:
- Complexity in maintenance
- Limited power potential compared to later fuel injection systems
- Sensitivity to fuel quality and long periods of inactivity
🔧 Note: Modern fuel additives can particularly challenge CIS systems, potentially causing gumming and performance issues if the vehicle sits unused for extended periods.
By the late 1980s and early 1990s, Audi began transitioning to more advanced Motronic electronic fuel injection systems, which offered greater flexibility and tuning capabilities.
The legacy of CIS in Audi's engineering history is a testament to Bosch's innovative approach to solving automotive fuel delivery challenges. While it may seem antiquated by today's standards, CIS represented a crucial evolutionary step in automotive technology.
What does CIS stand for?
+CIS stands for Continuous Injection System, a fuel delivery method developed by Bosch that continuously sprays fuel during the combustion cycle.
Which Audi models used CIS?
+Most Audi models from the mid-1970s to late 1980s used CIS, including various 5000 and 200 series vehicles with both naturally aspirated and turbocharged engines.
Why did Audi stop using CIS?
+Audi transitioned to more advanced Motronic electronic fuel injection systems that offered better performance, easier diagnostics, and more precise fuel management.