RotaryEvolution

iTrader: (30)

then something isn't hooked up correctly if the leading isn't firing, try swapping the ignitor connectors on the distributor and see if it isn't just a faulty J109.

FunK73

iTrader: (6)

The leading ignition is functioning just fine.

Everything works fine except the tach and the 2 step.

RotaryEvolution

iTrader: (30)

oh well, so much for the old days of working 6A boxes, cheap new technology sucks.

FunK73

iTrader: (6)

Yeah I'm not sure where to go on this. I may try to swap out the box itself from where I bought it to see if that solves any issues.

Its just odd because the tach output wire is giving off some form of a signal (~7.5V) but is not enough to run the tach or work with the two step

j9fd3s

iTrader: (3)

just to be clear, when you're using the MSD tach out it is going right to the green yellow wire and its NOT still hooked to the coil, correct?

FunK73

iTrader: (6)

I can take pics to clarify but the gray tach output from the msd box is hooked directly to the green/yellow wire via the blue ended quick connect spade that is normally hooked on the - side of the coil. The coil is not connect to the tach signals, however the + wire is hooked up but the ignitor is not connected so it shouldnt be getting any power

rx7lives

I would avoid connecting the stock tach wire to the leading's coil. Remember, the MSD isn't sending one pulse per fire but multiple (does anyone know how many?) so all the tach is seeing by connecting to the leading coil is a lot of electrical noise. Say the MSD puts out 5 pulses per the normal 1, that means the stock tach is seeing a higher pulse count as well as a shorter pulse width.

I would connect it to the tach output on the MSD unit. Why aren't you using the stock trailing coil, dist and ignitor? That's how my (older 6A) unit is set. MSD on the leading and the trailing is stock although I took someone here's advice and put the trailing leads on the leading spots on the dist cap. I should try both ways to see if there's a difference. I seem to remember that on the combo dist (leading and trailing on one dist) the leading had better contacts between the rotor and the cap.

You're getting the 7 volts from the tach out on the MSD? You could use a simple transistor and resistor circuit so the stock tach sees the voltage it's supposed to see.

Try reconnecting the trailing circuit and see if the tach works. You don't lose anything by having the trailing coil and plugs working, but you do end up with a bit less smog. If that doesn't work and you see sparks from the internal electrode to the ground one on a grounded test spark plug (not near any fuel!), then you've got a problem with your tach circuit. I forget what year your '7 is but if it's an '84 or '85, I've got an extra tach somewhere you can have if that's the problem. It could and probably is the circuit on the circuit board on the back of the cluster if it doesn't work setup as stock. Assuming it's an '84 or '85. I don't remember how the earlier ones were set up.

If the tach works by hooking the trailing back up, problem solved if you want to leave the trailing connected.
If not a simple transistor switch should solve your problem and it shouldn't take me more than 5 minutes to design if you get me all the voltages, car year and the type of MSD you're using.

Good luck!

FunK73

iTrader: (6)

The trailing is not hooked up because of the built in limiter. If I hit the limiter on a missed shift for instance, itll cut leading of course, and thus start to detinate on the trailing. Ask Peejay how that goes lol.

The tach still functions fine when its hooked up the factory way. It just doesnt do squat when the msd is hooked up to it

RotaryEvolution

iTrader: (30)

the leading tach signal is fine, it is picking up the same amount of revs as the trailing ignitor, with the exception of having it wired up to waste spark it is firing 2 coils. but that makes no difference to the tachometer. if you were to try and pick up a tach signal with a probe from the leading plug wires though, that is a different story and the figure would need to be halved and would be erratic.

FunK73

iTrader: (6)

So this is getting interesting. I got the tach to work. But not in the way I was thinking lol.

So I connected the trailing coil, but not the trailing coil. Then I hooked the tach green/yellow wire to the tach output from the box, along with the 2 step box, per msd wiring diagram. Now when I flip on the 2 step box, the tach come alive. However in the 2 step box is off, or if i unplug the trailing ignitor, the tach dies. My guess is maybe the extra voltage from the 2 step box on that wire was enough to bump it up to 12v?

The 2 step still doesnt work though. Hit the trigger switch, LED comes on saying the 2 step rpm limit is active, but the car revs right on past it. grrrr

rx7lives

Have you called MSD? They must have one of the best tech support lines in existence. I needed the schematic for an ancient MSD and they still supported it and had the one specifically for an Rx-7, the ones I posted and I waited on hold for less than a minute. Of course they have you using two MSDs and since mine doesn't have a rev limiter, I just left the trailing stock except for the HI leads which I put on the leading plugs outputs on the dist.

I'd like to hear how the rev limiter works when you get it working; does it cut off the spark completely or limit it? What RPMs are you setting it to?

FunK73

iTrader: (6)

I have not had a chance to call MSD yet since I'm working the closing shift at Porsche at the moment. They just happen to be open only when I'm at work. I emailed them with no response and I tried to register to their support forum twice and each time the admins declined activating my account.

The limited does cut ignition completely. It essentially cancels enough of the spark signals to keep the car from exceeding the limit. As far as sounds, think like gunshots with fire ***** too.

The limiter is set at 8k at the moment but I will be setting the 2 step to 3-4k. That is the only thing not functioning now.

I swapped out the 6al for a new one at the parts store. I plugged the new box in to the old wiring harness and now the tach is working off the tach output no problem. The 2 step is still not working but at least the tach is for now.

Its a little odd. Before the 2 step box LED flash when the 2 step was turned on, and stay lit when the activation wire got 12V.

Now when the 2 step box is turned off, the LED is lit very dimly (almost looks like it is reading the sparks, it flashes similarly to the LED on the 6al itself) and when I turn the box on, the LED flashes and turns off, and then of course stays lit when activation wire gets 12V. Its all rather odd and I will be contacting MSD as soon as I can.

rx7lives

Sounds like progress.

How weird is it that the tach output was bad on a new unit? Is the 2 step box new as well? It's cool that the parts store let you swap out the box without the harness.

Please keep us updated.

The first MSD I installed for a friend's Mustang went bad in the late 80's I believe, in less than a week???

FunK73

iTrader: (6)

Yeah no kidding. Needless to say I have a pretty good relationship with my local O'Reillys. I'm in there A LOT lol.

The 2 step is also brand new. Ordered from Summit so who knows. Just a matter of me getting a hold of MSD now. Hopefully theyre not like SEND US EVERYTHING TO LOOK AT! cause that would REALLY suck to pull it all out of the car

Jeezus

iTrader: (4)

Easiest way to do this:

Dizzy wiring: There is a red and a green wire from the leading. Use the purple and green wire from the MSD box, connect the purple MSD to the green of the dizzy, the Green MSD wire to the Red wire on the dizzy. You now have signal.

For the kill switch, use the white wire from the MSD to a switched ground. When the switch is on, the wire will be grounded. This will allow the car to crank and not fire.