Hi all,
Has anyone been able to decode the ECM's fuel pulse signal (green wire to speedometer)?
I bought a boat with 2006 BF150s last fall. Over the winter I upgraded all the electronics and added two Noland RS11 converters to digitize certain things (RPM, trim, temps, fuel level, fuel consumption). Late in the project, I learned that the Nolands can't read the Honda fuel pulse signal, they can only read pulses from a flowmeter. So I built a circuit that can convert a PWM signal into a variable frequency, simulating a flowmeter (I was trained as an electrical engineer years ago and felt up to a challenge). Problem is, now that I'm finally commissioning everything, I can't seem to get a readable signal on the green fuel pulse wire.
-My Fluke meter reads 0 volts, 0 Hz frequency, 0% duty cycle on on the green wire, even at moderate load (~2,300 RPM, underway)
-The Fluke meter should be able to read this if its a PWM signal. When building my converter circuit I also built a PWM generator to simulate the engine (with 12V or ground pulses as short as 2-3ms and <1% duty cycle, resembling idle conditions), which the meter had no trouble reading
-Test LEDs in my circuit can be switched on to flash the input and output action, and they show no input
-The wiring between my circuit and the ECM connector is correct and solid, for both engines (and yes, I have the shop manual and have tested the correct pin on the ECM connector)
-Unfortunately, I was so over-confident in my design that I made a big mistake and already sold my digital speedo, so I can't use that to rule out bad ECMs. That said, the speedo worked fine, at least as far as fuel consumption is concerned, last fall before I started this project and I can't imagine that this function would have failed on them between now and then (I haven't done anything to short the green wire to ground or 12v, etc)
My last idea, which hopefully I can test today, is that perhaps the fuel pulse signal is TTL (transistor-to-transistor logic, which was used in the 1980's before modern CMOS technology was prevalent). In other words, I thought it would output 0V with 12V pulses, or possibly 12V with 0V pulses, but perhaps it outputs a current sink instead. Hopefully later today I'll try hooking it up to a crude, weak current source (the middle node of two resistors connected in series between the Black/Yellow ACC wire and ground, forming a voltage divider with a tiny amount of current flowing) and see if the green wire can pull it down to ground.
Otherwise... does anyone know how this works? It would be a shame to capitulate at this point and buy NMEA 2000 flow meters.
Ben