MS3X Tach Output

[SvenCS]

My tach was originally driven from the Neg side of a single 12V coil. I am now running wasted spark ignition on 6 cylinder BMW M30 engine. I currently have the recommended tach driver mods installed per MS2/Extra ignition description (which work).

However, MS3X now has Tach output. If I run this output directly from say the InjH or Tacho pin outputs, would this drive the original tach directly? In TunerStudio I can select which pin and then have the option of setting speed to Normal or Half.

Thanks,
Sven

[jsmcortina]

If your tacho needs a high voltage pulse then you will likely need to keep that circuit. If it is a 0-12V type, then use the "tacho" output with MS3X jumper JP3 installed.

James

[heychris_1]

Does it makes sense to use a MSD tach adapter to recover the signal?

[jsmcortina]

Does it makes sense to use a MSD tach adapter to recover the signal?

Depends on what it does. If it converts a 0-12V signal to a signal suitable for high voltage tachs then it sounds worth a try.

James

[heychris_1]

My understanding is that MSD does have an adapter for this, but my guess is it's easier to do it inside the MS3.

Do most people typically put the diodes inside the box or on the spark harness?

[SvenCS]

I put the diodes on a proto board in a separate case along with the ignition driver board and EGT Quad board (not installed yet). In the first iteration I had installed the diodes in a relay case located near the wasted spark module. Three wires in (one from each ignition driver) and one out to the existing tach.

[heychris_1]

To clarify, even with ls2 coil per cylinder, the correct wiring is still only spark A and spark B input into tach lead. Correct?

[heychris_1]

Sven,

How did you do you hall sensor distributor? Which wasted spark coil pack are you using?

[jsmcortina]

The diodes method will not work with LS coils.

James

[heychris_1]

How do I get a tach output if I use LS coils?

[jsmcortina]

It all depends on your tacho. I'm using a standard Rover SD1 V8 tacho and it works fine with the 0-12V signal. I'd expect all aftermarket tachos to work ok.

It could be worth trying that MSD tacho adapter if not.

James

[SvenCS]

heychris,

I am using a 3-coil pack (Bosch 0 221 603 002). The geartooth hall sensor (Cherry Electric GS100701) is mounted to a custom bung welded onto the side of the upper timing cover (see photo). The internal distributor gear drive that is attached to the end of the cam shaft has a single pin set/glued into a receiving hole that the sensor is aimed at.

Sven

[heychris_1]

An MSD 6al has a tach output described as: "The Tach Output Terminal
produces a 12 volt square wave signal with a 20% duty cycle"

Is that similar to the tach output of the ms3?

If so, the MSD8920 tach adapter could work.
http://www.msdpowersports.com/pdf/frm22049_pn8920.pdf

If MSD can do it, I'd like to see us figure out a way to mimic their circuit.

Has anyone else gotten this to work?

[jsmcortina]

An MSD 6al has a tach output described as: "The Tach Output Terminal
produces a 12 volt square wave signal with a 20% duty cycle"

Is that similar to the tach output of the ms3?

Similar, but MS3 is 50%. I would expect the tach adapter to work.

James

[heychris_1]

Is there anyone else that has this working?

[heychris_1]

Would the circuit listed work? I'm pretty sure having a coil in there is important. When I connected my crane Hi-6 ignition system many years ago I had to put a coil into the system to keep my tach working. That coil went from +12V to the negative trigger lead on the points as well as the tach.


http://www.msextra.com/doc/ms1extra/MS_ ... m#tachoout

[prof315]

I might work. I had 1 success out of almost 40 relays tried trying to make it work with a German VDO factory VW tach originally run from coil negative. What will work for sure is using a mainboard BIP373 to drive an old school ignition coil and taking a tach signal off of the primary negative.

[heychris_1]

I wonder if the issue is the size of the coil. given the size of the coil necessary to make my crane work, I bet I could just substitute that for the relay's coil.


I wonder if I could either use the crane coil or add a large inductor like this:
http://search.digikey.com/scripts/DkSea ... =M10029-ND

Do we have any electrical engineers that could weigh in on it?