I just finished up building an fcd following those instructions but now I have a problem, where does the Vref lead from the fcd connect? I know where to connect power/ground and you cut the signal wire for the in/out but I have no clue what to do with the Vref wire, will it still work correctly without this connected?
#101573, "RE: Do-It-Yourself FCD Wiring Help" In response to Reply # 5
I have the schematic for the three wire one just like Mike posted above. You dont need to over engineer the FCD. The ones Paul makes work well as well. They both do the same thing only one is made to be more complicated than the other.
#101577, "RE: Do-It-Yourself FCD Wiring Help" In response to Reply # 6 Sep-29-07 01:56 PM by Nightfall
Just wanted to update my progress. At first I couldn't get this fcd to work, turns out I was confusing the map Vref and signal wires yeah I had a retarded moment, but it happens to the best of us right lol. Anyway, this fcd DOES work very well if it is built AND connected correctly. Well worth the couple dollars it took to assemble. Thanks again Paul for posting your installation instructions, would have never caught my mistake without it
Originally posted by Star Turbo Talon I have the schematic for the three wire one just like Mike posted above. You dont need to over engineer the FCD. The ones Paul makes work well as well. They both do the same thing only one is made to be more complicated than the other. Terry
Do you mind posting it up, I'm interested to see what that one consists of too.
#101582, "RE: Do-It-Yourself FCD Wiring Help" In response to Reply # 7 Oct-01-07 05:39 PM by VelocitaPaola
There ya go...
Not more than $3 in parts or so...
Terry, obviously I don't think mine, or other more complicated FCDs are "over-engineered." Not all voltage clamps are created equal. By using slightly more complex circuitry we can achieve features such as noise filtering, high input impedances, low output impedances, and more reliable clamping.
Diode-diode-pot FCDs get the job done, but they're a "quick and dirty" solution. The clamping voltage can vary, and there tends to be more instability at the threshold. Picked up noise will also be transmitted directly to the ECU.
Here are a couple of representative graphs...
Sorry if I made that sound like one giant marketing pitch, but there is a difference between FCDs. My recommendation to anyone using an S-FMU, FMU or PortFueler would be to invest in a quality FCD. If you plan on upgrading to MS in the future, get the cheapest one you can find.
#101610, "RE: Do-It-Yourself FCD Wiring Help" In response to Reply # 8
Interesting Paul.....too bad myself as well as many others have not noticed any instability or noise at the clamp voltage. Yes you are making a marketing pitch. I have never had an issue with mine and I know many others havent either so making it more complex is just a way for someone to argue points that really are nothing more than a waste of time and float thier own boat.
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yeah I had a retarded moment, but it happens to the best of us right lol. Anyway, this fcd DOES work very well if it is built AND connected correctly. Well worth the couple dollars it took to assemble. Thanks again Paul for posting your installation instructions, would have never caught my mistake without it 
