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FORD BRONCO -> ELECTRICAL; EEC/PCM, Self-Test, wiring diagrams... -> Electronic Engine Control (EEC); SELF TEST & Diagnostic Trouble Code (DTC), OBD II, etc. -> EEC I & EEC II
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Electronic Engine Control (EEC) Overview, Ford; EEC I & EEC II; "...These two "modules" used a common processor and memory so they can be described together. The processor was a 12 bit micro manufactured by Toshiba. The Ford internal code name for it was "PM-11" or "Poor Man's 11" implying it was a stripped down version of the, then popular, Digital Equipment Corporation PDP-11 computer. A PDP-11 was used in a vehicle in the first half of the 1970s for "proof of concept". In reality there was very little in common between these two computer architectures. This chip was never commercially available. This 12 bit processor was the only commercially available chip to feature all four mathematical functions (addition, subtraction, multiplication and division) at the time. The choice of 12 bits was not accidental. For accuracy, it was determined that formulas needed to be able to resolve 1 part in 1000 or about 10 bits. Another bit was required for sign. This, logically, was rounded up to 12 bits which also resulted in an address space of 16 kilo-words. There was no "stack" for subroutine calls and returns. Rather the Instruction Pointer Register was "swapped" with another register that had been previously filled with the address of the target subroutine. Returning was accomplished by swapping back. All code was written in assembly language. The EEC-II controlled air-fuel ratio via the Ford proprietary model 7200 Variable Venturi (VV) Carburetor. This was the last carburetor designed and built by Ford US. It was considered to be the pinnacle of carburetor design. Air-fuel ratio was controlled by a stepper motor that operated a rack which moved a pintel that opened/closed the float bowel vent. When closed, no air could enter the bowel and the carburetor was lean. When open, the carburetor was rich. While this carburetor worked well, it was extremely expensive to manufacture. Each carburetor was hand calibrated in a pressure controlled room..." Read More
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