So after thinking about it if the ECM is wanting to maintain a 1 amp current and the resistance of the coil is 3ohms then it will require 3 volts minimum to maintain on. So the voltage drop will always be constant across the injector at 3 volts and that means more or less constant 3V drop across the injector pin. So for a basic proposal for how to measure a constant voltage drop
Code:
12V
o--------|
|
|
z 3V Zener
A LM741 op amp
|
| |\|
o----------------|+\
| | >- out
INJ -------)----------------|-/
| |/|
.-.
| |
| | 10k
'-'
|
|
===
GND
This could be an add on board in front of the stock MPGuino if the op amp had 12V and gnd hooked up. The biggest problem is that a 3V zener is pretty hard to find so a slight modification to the circuit will let it be tuned from a 0-5V drop...
Code:
12V .--------------.
o--------| |
| .-. 100k pot
| | |<------.
z 5.1V Zener | | |
A '-' | LM741 op amp
| | |
| | | |\|
o--------------' '-----|+\
| | >- out
INJ -------)-----------------------------|-/
| |/|
.-.
| |
| | 1k
'-'
|
|
===
GND
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
That gives us a way to precisely calibrate the voltage drop.
All the peak and hold injector circuits I could find are 12V > fuse > injector >ecm(gnd) so measuring INJ at the ecm and assuming the 12v going into the mpguino is not significantly different than the 12V side of the injector this circuit should work. I will build one tonight and test it once I can get the van out on the road after the blizzard goes away. If this works it could be added to the standard circuit but it is adding a good bit more mess to it. It should be a 100% solution though
