Automatic Computer-Controlled Calibration of EFI Control Units

Calibration testing of the Electronic Control Unit (ECU), a sophisticated analog computer which controls injector operation in the recently introduced domestic-passenger-car Electronic Fuel Injection system, is accomplished at a series of test stations equipped with specially designed, computer-controlled Automatic Test Equipment (ATE). This paper outlines the overall test sequence to which an ECU is subjected following manufacture, and then describes in detail the design logic, hardware, and software associated with the two ATE systems used. Particular emphasis is given to the Trim Station ATE, which not only performs complete functional testing but also computes optimum values for 28 resistors incorporated into the circuit at this stage to optimize circuit performance. These values are transmitted to the Laser Trimmer, which cuts individualized resistance modules for each ECU. After module insertion, the ECU is retested, packaged, and final-tested. The identical Second Test Station and Final Test Station ATE systems are electrically similar to the Trim ATE but have no resistance-optimizing capability and are fixtured to accommodate up to ten units at a time.