In the auto industry, ECM stands for Electronic Control Module. ECMs are small computer chips that control the fuel metering and timing of the fuel injector. The chip determines how much fuel your GM needs and how quickly it needs it by analyzing factors such as your engine's crankshaft position, the revolutions per minute at which it is running and its intake air temperature and boost pressure. Throughout the years, GM has used three main types of ECMs: C3s, P4s and Flash ECMs. You can program your ECM or buy a custom tuned EMC to improve the fuel efficiency, acceleration or towing power of your GM.
Strictly speaking, all GM ECMs are C3s, because C3 stands for Computer Command Control and that is what an ECM is. However, C3 ECMs have come to describe older ECMs with a fixed Read Only Memory and a removable memory, which contains the tuning specifications for each application. ECMs in this category include GM's 1225550, 1226026 and 1226458. These are used on the 1982 5.0 V8 CFI "7" LU5, 1983-84 2.0 L4 TBI "P" LQ5 and 1984 2.0 L4 TBI "P" LQ5 engines respectively.
The next generation of GM ECMs included engines controlled by electronic control modules with one electronically programmable read-only memory which contained the vehicle's calibration and program code. Unlike the previous C3 models, EPROM memory modules can be erased and reprogrammed to your specifications. EPROM modules have a special window that allows you to erase the data on the module if you expose it to ultraviolet light. P4 ECMs include the 1227165, the 1613487 and the 16196395 chips.
The latest generation of GM ECMs are made of flash memory modules which can be easily reprogrammed to your desired specifications. This is an important upgrade from P4 ECMs, which although reprogrammable in theory, were cumbersome to tune up and were not really designed to be modified. GM ECMs with flash memory include the 16188051, the 16211539 and the 16214399, which control the 1994-95 5.7 V8 TPI, the 1996 3.1 V6 SFI "M" and the 3.1 V6 SFI "M" L82 engines, respectively.
