FD ignition, coil wiring help please
 

I'm trying to wire a 13b-rew ignition system into my FC (along with a 13b-rew engine).

I have the following: Ignitor, Coil packs, coil wiring (early 93), condensor.

There was a recent thread about why coils go bad which came to the conclusion that its due to constant grounding, and yet my coil pack has the grounds right at the coil. Am I reading this wrong, is the ground at the coil switched somewhere and only used to kill the engine?

Please see the attached diagrams, one (the crude one) is what I am wrighting up to assist me in wiring in the FD ignition.

The other is the stock wiring diagram which covers this section.

Ok I relised that there is no way the grounds can work that way comming off the coils in the above picture unless they go to a resistor, or thats part of a kill switch function, and even then they would have to be independant of each other when that function was inactive.

so revised picture

Tach output? I can't see your factory wiring diagram but there might be a feedback signal going back into the ecu.

The tach output isn't part of the factory diagram. I believe the factory ecu normally drives the tach, but there is no reason not to drive it from one of the trail ign coils.

Thats basicly how you set up any aftermarket tach, depending on firiring mode it could connect to the lead coil but I think that would double the RPM shown on the tach in this case because of wasted spark.

Your right, I forgot the tach was drivin by the ECU, have you checked to see if theres a feedback wire going into the ecu as the second wire to the coils?

I know what you mean, but I can't find one, I guess it doesn't have a feedback.

Ok, opened up the service manuel pg z-28, looks like Black/red is power going into the coils...

L/W, R, and Y/L are all the ground wires that go to the ignition moduel, the moduel is the gate system that allows the coil packs to be ground at specific times. I was thinking about the wires that go into the moduel of the second gen.

Does this make sense?

Also the dotted line is shielded wire. The ground wires that go into the ignition moduel are shielded that means they have a wired strand outside the regular wire and those outer wires get grounded to the chassis at some point. I think that may have been confusing you.

I see what you mean its showing where the shielded wire is connected to ground.

Thanks...

I think you want the tach on the L coil (at least that is where I pull from on the Haltech)

I also think you are thinking too hard...unless I don't understand you.

Power the coils and ignitor straight from a switched source...since you are going custom, why not B+ via a relay.

the ECU sends a GND signal to the ignitor which inturn fires a coil.

The conclusion that you cite above is wrong. Grounds have nothing to do with this. Note that portions of the factory harness contain resistance wire in it. This is necessary for an inductive discharge ignition to function properly. If you don't use it, then you need to put an external resistor in the coils' primary circuit or you will suffer the consequences of coil and ignitor melt down.

There are no grounds on the coils, per se as shown on the factory diagram. The grounds shown are for shielding on some of the ignition harness wires.

Thanks for the input, I'm curios why isnt the resistance wire shown in the factory diagram?

Also a resistor is not needed for an inductive ignition to function, or the resistor is allready built into many factory coils.

Care to do me a favor and measure the voltage of the primary wire before the condensor in comparison to the battery with the engine on, not running. This should give me an idea what size resistor is required

Hey, didn't know about the resistance wiring. Makes me feel like my aftermarket ignition system was the best way to go! God, why do they have to complicate things so damn much! (Don’t answer that, not in the form of a question)

Yea, neither did I until I cut into the harness and discovered alloy wire (e.g., nichrome) while I was putting an MSD on the leading coil.

Probably an oversite--my quess is that it was called out in the harness spec, but never made it in the FSM drawings since it's not a separate part.

Indeed the resistor is internal to many coils. I've measured the FD's and they are all 1/2 ohm or less, so no resistor in them. The ignition will run without the resistor; however, you will saturate the coil and overheat the coil and ignitor. The purpose of the reisistor is to provide current limiting.

I'll check when I have a chance, but I don't think the Ignitor is gated on when the engine isn't actually running; so there wouldn't be a load on the coil circuit. (Unlike a points type distributor.) I can tell you from experience that about a 1 ohm (20w resistor) would be a good place to start.