Speeds and you let off the gas, a leaner air/fuel mixture is required in order On systems utilizing a Mass Air Flow (MAF) sensor, the computer looks at the MAFĪnd TP sensors to determine accel enrich mode operation.Įngine is decelerating, such as what would occur when the car is at city driving Initiate an “Accel Enrich” event, and how much enrichment and how long to On speed density fuel injection systems, the ECM looks at ManifoldĪbsolute Pressure (MAP) and Throttle Position (TP) sensors to determine when to Moment, the engine would stumble due to a brief lean condition. If an extra amount of fuel was not delivered to the engine at this
This fuel gets briefly trapped on these surfaces and doesn’t make it into To condense on the manifold and intake port walls. When the throttle is opened, a rapid increase in manifold pressure causes fuel
With fuel injection, this function is still required for the engine to run Were a carbureted engine, this mode would be known as the acceleration pump Sensor inputs to make adjustments to the fuel delivery based on what it sees in Sensors/inputs to determine fuel delivery to the engine, but now it uses the O2 When the system enters closed loop, the ECM still uses all other Heated O2 sensors, these qualifiers are usually much less. For most non-heated O2 sensor applications, the general value for coolant The amount of coolant temperature and elapsed time from startup qualifiersĭiffer from engine to engine, and differ a great deal depending on whether theĮCM is working with a heated or non-heated oxygen sensor. Into the PROM memory are set qualifiers the ECM uses to determine when to enableīesides O2 sensor output voltage change, these qualifiers are coolant Whether or not it is ready (hot enough) for closed loop mode. The ECM uses to determine how much fuel to give the engine in this operatingĮCM still constantly monitors the signal coming from the O2 sensor to see Making fuel delivery calculations and relies on the other sensors to determineĪre specific tables stored in the PROM programming that contain the instructions During open loop operation, the ECM ignores the O2 sensor input when Started and the RPMs go above 400rpm (and is not in clear flood mode), the ECMĮnters OPEN LOOP fuel control operation. Mode, the ECM operates in two conditions commonly referred to as OPEN and CLOSED Temperature and other factors it normally uses. Throttle position falls below the 80% threshold or RPMs go above 600, the ECMĭisables clear flood mode and calculates fuel delivery based on coolant In clear flood mode as long as the throttle is 80% or higher and the RPMs are In this mode the ECM commands a delivered Air/Fuel ratio to very lean Will enter what is called “clear flood mode”. Reason the engine should become flooded, provisions have been built into theĭuring cranking of the engine you depress the throttle more than 80%, the ECM Ignition spark advance and IAC valve position output functions use The higher the coolant temperature, the leaner the Air/Fuel ratio. Temperature, the richer the Air/Fuel ratio. Pulse width (amount of injector ON time) it needs to command the fuel injectors Programming) which are based on the coolant temperature to determine how much It receives reference pulses (indicating the engine is turning over) it will useĪir/fuel ratio values stored in the cranking fuel pulse tables (in the PROM Next, the ECM waits until it receives reference pulses from the The fuel pump is activated for 2 seconds to “prime” the system. Very short amount of time, usually much less than 1 second after the key is What is known as “quick start” (obviously helping the engine startup more Some later ECMs also pulsed the injectors during this period to aid in Operates within determined by time, temperature, and engine operating load.įirst key on the ignition, the ECM loads the information off the PROM chip and In addition to these core functions, there are modes of operation the ECM
#Injector cranking primer enrichment evom software
Stored in the main memory chip (PROM) is the software (values programmedīy GM or your custom tuner) that tell the computer, among other things, how muchįuel and spark to deliver to the engine for a given set of operating conditions. The ECM is a simple computer that runs software programs. Article explains the core functions of the ECM.