Another 911SC tach problem

[Jared at Pelican Parts]

So I tied in the MSD tach adapter to the black/purple wire last night. Tach works, however, when I go to drive the car, as soon as it hits 3500 RPM, the whole ignition cuts out and the cars stalls until it drops back down under 3500RPM. It almost feels like a limiter on there. Anyone have any ideas? Might I need to install a ballast resistor in line?

[emcon5]

Isn't that where the MSD switches from multiple to single spark?

Tom

[Jared at Pelican Parts]

Im not sure. All I know is that I gotta get the tach working asap.

[Eugene at Pelican Parts]

What an odd problem... I think MSDs switch to single spark at 3000, but that's close enough. If you regapped the plugs, maybe you opened them up too wide and you're only getting a burn under multiple zap. If you think feedback from the tach is causing it, then maybe you should try bypassing the tach adapter since it is unnecessary for an SC. What kind of ignition wires are you running?

[Jared at Pelican Parts]

Magenecor wires. Should I run the black/purple wire directly to the positive side of the coil?

[si2t3m]

Here is how i'm setup with my 3.0L

Big red wire from msd box to battery
black wire from msd box to battery
red wire from msd box to 12v switched

2 wires going to the coil + and - (don't recall the color and car isn't near me).

Violet and green wires connected to the shielded green wire coming out of the dizzy (one on the sheild, one on the signal). reversed polarity on these and car runs like crap.

Black/purple wire connected directly in the msd box in the tach output. No tach adapter needed for me.

HTH

Marc-André

[Eugene at Pelican Parts]

Originally posted by si2t3m
2 wires going to the coil + and - (don't recall the color and car isn't near me).

On my Crane, the coil wires were orange and black. MSD should be the same.

I think MSD has a port for the tach output where my Crane had a green wire. Either way, the black/purple connects directly to the ignition box.

[Jared at Pelican Parts]

Ok, I get it now, just put a female spade on the black/purple and then plug it into the MSD.

[dhoward]

That's what I said in the first place!!
BTW, don't be tempted to hook the tach back up to the coil. If I recall correctly, you're looking at a little over 400 volts on the primary side....

[CamB]

Yep - try the black/purple on the MSD box (per the other thread(s)).

If it is the rev limiting MSD box, and you have a 6000rpm pill in there, you would expect it to rev limit at 4000 rpm if you snipped the two wires under the gromment (for 4 cylinder operation) rather than one wire (for 6 cylinder). Just a thought.

[Jared at Pelican Parts]

its a 6A so no rev limiter. I just hooked the tach up directly to the box, and so far no problems.

[Jared at Pelican Parts]

Ok, so i plugged the signal wire directly into the MSD box and it now works perfectly, THANKS GUYS!

[Lorenfb]

All those headaches because you guys switch from the good Bosch
units and put that klug in your cars. Is there any hope for you all?

Jared, talk to Tom. He's got a good Bosch CD in his office. If not,
he can get one.

Have Fun
Loren
'88 3.2

[Jared at Pelican Parts]

Actually, we went through about three CD units before going to the MSD.

[Lorenfb]

Sounds like you got another problem, Jared!

The Bosch CD is the simplest and most realiable unit.
You need to remember the failure rate of any system is
directly proportional to the number of its components,
and guess what CDI has about 10X as many components
as a Bosch unit?

Always carry a spare CDI, when not using a Bosch unit!

Have Fun
Loren
'88 3.2

[1fastredsc]

Damn loren, you really have something against msd's? I think they are quality units, and my friends 944 has one and the low end was greatly improved, it even starts much faster believe it or not.

[Jared at Pelican Parts]

I have to say that the car does start much quicker with the MSD.