more questions about details

[John T Stein]

On 3-7 Chris Adam Thomas wrote:
 
> A few more questions:
>
 
> What is the usual form and typical range of sensor values input to the ECM from:
> 
> 	Manifold absolute pressure - MAP
> 
> 	Throttle Position switch - TPS
> 
> 	Engine rpm
> 
> 	Engine coolant temperature
> 
> 	Manifold air temperature - MAT
> 
> 	Electronic spark control (knock sensor?) - ESC
> 
> 	Idle air control - IAC  (?)
> 
> 	Ignition voltage
> 
> and for:
> 
> 	Stoichiometric & Linear Lambda
> 
> 
> Also what whould "SDF or staged SDF injector firing" mean?
> 
> Again; all assistance is appreciated
> 
> 
> cat
> 


Speaking only for  General Motors engine controllers, these  ECMs power most of their  sensors
 with +5 volts, as a result:

(1) MAP ranges from about 0.8 volts to 5.  Some GM MAP sensors 
produce increasing voltage with increasing  vacuum, some with 
increasing pressure.  Output voltage is an  essentially linear 
function of vacuum/pressure.  Since the ECM can monitor the 
(nominally) 5 volt supply it "knows" what one end of this function 
is, the initial  accuracy and stability of the sensor establishes the other 
end.. 

(2) TPS is a potentiometer hung between the +5 volts and ground.  
WOT corresponds to ~ 5volts, closed throttle about 0.  The ECM 
calibrates itself to the closed throttle level by looking at RPM, 
deducing when the engine is at warm idle, and noting the TPS voltage.

(3) MAT and Coolant temperature sensors are negative temperature 
coefficient thermistors.  The thermistor is part of a voltage divider 
which is "powered" by the +5 volts from the ECM.  The voltage at the 
node in the middle of the divider is monitored by the ECM.  I can 
look up the resistance vs. temperature characteristic for the 
thermistor if you're interested, it is highly nonlinear.

(4) If you've been following the ongoing discussion re. knock sensors 
you know they are essentially piezoelectric accelerometers which 
"listen" for the sound of knocking.  Their output is not directly 
useable and some form of charge-to-voltage signal processing is used 
before the signal is supplied to the ECM. If I remember correctly  the signal which 
eventually goes to the ECM is nominally 5 volts and is  negative-going with "knock".

(5) IAC -- These are outputs from the ECM not inputs to it.  They go  to a stepper motor which 
controls a path for idle air to the engine.