MSD 6AL, 8762 and '87 930 tachometer

[JFairman]

I've installed an MSD 6AL and MSD 8762 boost retard box and the car runs but the tach does not work.

I just barely get by when it comes to electrical stuff and much prefer mechanical things.

Anyway, I think I've read that some of the later cars and mine is an '87 930 don't need a tach adaptor for the origonal tach to work.

Does anyone know if I have to install a tach adaptor or do I add another wire(s) somewhere to make it work without one?
Does the origonal skinny black/purple tach signal wire in the harness connect to the MSD somewhere, like the single lone spade terminal on the side of the 6AL box?

I searched and read some posts but I can't find a definitive answer.

thanks in advance,
Jim

[cole930]

Jim,

There should be an open male spade connector on the back end of the
6AL, that is the tach output. Run a wire from it to the viol/ Blk tach wire in the 6 pin engine conn. Try it and see if the tach reads correctly, if it doesn't read correctly, you will need a tach adapter. Also make sure you mod the rotor if you are not using a non rev limiting rotor and don't forget to regap the plugs.

Cole

[JFairman]

Thanks Cole, I'll try that.

I soldered in a copper jumper in the rotor and it's working.

I've got Bosch W4CS silver plugs in there and they have the type of offset ground electrode that can be bent to adjust the gap.
Any ideas how far the plug gap can be opened up before it's too far and starts missfiring, or what is optimum?

I have an MSD Digital 6 ignition in an old 3.5 liter BMW engine and I have the plug gaps in that around .050" but I think that would be way too big with the combustion chamber turbulance in a 930 engine.
I had to use an MSD tach adaptor in that car but it's a 1978 model and the tach electronics might be more primitive than the '87 930 tach, or maybe not.

thanks again,
Jim

[mark houghton]

$hit Jim, and I just shot you an emai! Cole beat me to it.

I'm using these high-faluting NGK race plugs and if I recall I gapped them at .040. MSD suggests .050, way mucho I think.

[cole930]

I'm going to attribute your slowness to react to Jim's post to the hobbling you had to do to get to the computer.

Cole

[mark houghton]

That's my excuse, and I'm sticking to it!

[cole930]

Jim,

Mark meant to tell you if you need a tach adapter the one you want is
the 8920. He will tell you the pain he is presently enduring is distracting
him.
Pretty wimpy excuse though, needs something more like the side effects
of 6 months of chemo.

Cole

[JFairman]

Ran a jumper wire like described and the tach works!

Weird thing is I never touched the distributor and with all the MSD stuff installed the timing is advanced alot.

The car had a good working silver box permatune in the car when I got it and it still works fine but I wanted to do this MSD upgrade..

I wonder, is it possible that the MSD electronics are that much faster or does the permatune electronics delay the spark?
Doesn't matter of course since you can compensate for it by turning the distributor.

..and something in the fuel pump relay and wiring circuit still has a mind of it's own so I have to bypass all that miserable yellow relay crap and rewire them directly to the ignition switch.

This halloween party is why I was a bit slow to get to the wiring today. . .
..still recovering.

[cole930]

Now that's even a better excuse than the 6 months of chemo. Excuse totally
accepted,

Cole

[mark houghton]

That does it, I'm moving to Florida. Can I be your neighbor?

[John at J&S]

You could have the magnetic pickup wires reversed. An MSD tech note says wire it one way, note the timing, then reverse the wires and check timing again. The connection that results in the least timing is the correct way. The difference could be twenty or more degrees, so you may have to move the distributor to get the engine to start when you switch the connection.

The fuel pump relay may have an internal tach circuit that shuts off fuel if the engine is not running. An 8910 tach adapter should fix that.

[Ken911]

You know it has it's faults but there is so much of this type of stuff going on here all the time I just love florida

[JFairman]

[QUOTE=John at J&S;4986739]You could have the magnetic pickup wires reversed. An MSD tech note says wire it one way, note the timing, then reverse the wires and check timing again. The connection that results in the least timing is the correct way. The difference could be twenty or more degrees, so you may have to move the distributor to get the engine to start when you switch the connection.]

Thanks John,
I turned the distributor back to where it was, reversed the purple and green MSD magnetic pickup wires to the green coax distributor wire and it fired up and runs like before.
It did free rev in nuetral with a bit more pep with the timing advanced 20 something degrees.. Of course now with the timing back to normal it revs lazy as ever.

I got the ignition box second hand with no instructions and the PDF instructions for the 6AL I found online didn't mention how timing will be advanced so much with the trigger wire polarity reversed.

[mark houghton]

[QUOTE=JFairman;4990024][QUOTE=John at J&S;4986739]You could have the magnetic pickup wires reversed. An MSD tech note says wire it one way, note the timing, then reverse the wires and check timing again. The connection that results in the least timing is the correct way. The difference could be twenty or more degrees, so you may have to move the distributor to get the engine to start when you switch the connection.[QUOTE]

Very interesting. I didn't know that (my MSD6AL was already installed when I bought the car) and there is no reference to that little tech note in the installation instructions.
If Jim was getting 20 degrees advance with the wrong connection, it makes me want to try reversing my wires to intentionally get more advance...since I'm out of distributor rotation room, maxing out at 8 BTDC when I would really like something closer to 12 degrees. Maybe reverse the wires, then twist some distributor retard in to get the advance where I want it.

[John at J&S]

The BOSCH CDI triggers on the falling edge of the magnetic pickup signal. MSD triggers on the rising edge, so the pickup wires have to be reversed. Shield becomes +, signal becomes -.

Refer to the drawings here:
Distributor Pickups

[John at J&S]

Note there are two zero crossings in the waveform. You want the ignition to trigger on the sharper of the two.

The longer the waveform stays in the mid region, the more susceptible it is to false triggering and wandering timing.

[x98boardwell]

Screw the MSD... where the hell was that party at? if that was your house then I am on the first flight out. I would like a limo waiting at the airport when I arrive with the women from the party in it. What happens from there is up to us. All drinks and events on me.

Looked like a great time!

Bryan

[JFairman]

The party was at the Ann Norton Sculpture Gardens in West Palm Beach, Fl.
Their annual halloween party, Devils Night.

Alot of hot girls down here.

[rsrfan]

dibbs on catwoman...

[mark houghton]

Originally Posted by John at J&S

Note there are two zero crossings in the waveform. You want the ignition to trigger on the sharper of the two.

The longer the waveform stays in the mid region, the more susceptible it is to false triggering and wandering timing.

Great information. So are you saying that if I were to reverse the wires purposely to obtain more initial advance (just to give myself more adjustment room at the distributor) that it may end up on the flatter of the two waveforms and result in wandering/less precise timing? If that's the case I'll just leave it alone and re-index the dizzy. Be much easier to switch wires, though.