Status update on the MegaSquirt.
Got to step 50 of assembly and have another choice to make.
50. Next you need to make a decision. There are two input circuits for the tach signal:
• The Hall/optical/etc. circuit takes the square wave input from a Hall sensor, optical sensor, or points. It can also be used for triggering off the coil (but only if you are not controlling ignition timing).
• The VR circuit takes the AC signal from a variable reluctor sensor and converts it to a square wave for use by MegaSquirt.
Fortunately there is a chart that says Ford TFI and Ford EDIS use hall/optical/etc, but then there is another choice:
a: To install the Hall/optical input circuit (or points without a coil connection)
b: For triggering off the coil negative terminal/points
If I was just guessing I'd say TFI goes with option B and EDIS uses option A. Since EDIS uses a toothed wheel/hall sensor and TFI uses an Thick Film Ignition coil and distributor, but since they both have ignition coils... arrrr... It would be nice if someone was holding my hand on this. Going to just have to be confident with my intuition and go with option B. I'm assuming "triggering off the coil negative terminals/points" means the points in the distributor that the rotor short circuits to ground.
Even after reading
http://www.therangerstation.com/tech_library/TFI_Diagnostic.shtml
I'm unclear again, because it is about the TFI system and talks about using a Hall Effect sensor in the CMP (camshart position sensor). So not a physical rotor making short circuits, but a rotor with a hall effect sensor similar to a toothed wheel, but using a metal block to create a signal that the PCM (assuming = ECU) then considers among other factors to send the spark to the TFI ignition coil.
So the question is triggering points without a coil connection or triggering points off the coil negative terminal. So what is a point? The key to understanding my truck is in this sentence, I'm pretty sure, [ECU] returns a reference signal to tell the TFI module to switch the coil. Since my truck uses a coil then can I assume the points are triggered of the coil negative terminal since the other option is triggering points without a coil and I have a coil?
"The CMP sensor, housed inside the distributor, responds to a rotating metallic shutter mounted on the distributor shaft. This rotating shutter produces a digital Profile Ignition Pick-up (PIP) signal, which is used by the PCM and TFI to provide base timing information, determine engine speed (rpm) and crankshaft position. The distributor shaft rotates at one-half crankshaft speed, therefore the shutter rotates once for every two crankshaft revolutions."
This describes my truck "The second [TFI] configuration is known as a remote mount system, since the TFI is mounted on the engine or front fender apron. The distributor used by this system is sealed and houses the CMP sensor. The distributor does not utilize vacuum or centrifugal advance mechanisms; the ignition timing is automatically controlled by the Powertrain Control Module (PCM) and the TFI.
Ford calls this electronic ignition the Thick Film Integrated-IV (TFI-IV) ignition system. The TFI module is also known as the Ignition Control Module (ICM) which reports engine position and rpm to the PCM. The PCM then determines the proper spark timing and advance, and returns a reference signal to tell the TFI module to switch the coil, thereby by creating a spark. The PCM used on these vehicles is referred to by Ford as the Electronic Engine Control-IV (EEC-IV) module."
I'm overwhelmed now. My intuition has changed between option A and B too many times.
A: To install the Hall/optical input circuit (or points without a coil connection)
B: For triggering off the coil negative terminal/points
Best to step away from it and sleep on it or wait for replies.
Cheers!
PS. I'm sure this is painfully obvious to some or even maybe most people. Forgive my ignorance please. This is all very new to me. Except for soldering components on a board... that's the easy part!