Tacho issues

[ledgno1]

Hi all,

Has anyone installed an MSD 5 ignition along with a Blaster coil on their GQ Patrol or Maverick

If so, did anyone have the problem of the tacho no longer working as a result?

My tacho, when the signal wire is hooked up to the negative side of the coil as it should be bounces between 2 and 3 thousand RPM which is not relative to the RPM of the engine. If it's connected to the positive side of the coil as I've tried it's simply dead showing zero RPM.

Anyone have any ideas how I could solve this problem

Thanks....

[JeSTeROCK]

Could it be something to do with the original coil having a resistor. You might need to put a resistor in line to lower the voltage

[ledgno1]

Thanks for the suggestion - my sparky has tried a couple of different resistors to no avail at this stage.....

The car did original have a balast resistor however the instructions that come with the blaster coil tells you to remove it....

I'm tempted to wire it in again but don't want to either stuff the coil or cook the resistor???

Confused and frustrated

[chimpboy]

I doubt it has anything to do with the resistor.

I had not heard of MSD 5 ignition but I found this description online:

MSD 5 Ignition, PN 5200
The MSD 5 is our entry level multiple spark ignition control. This inductive discharge ignition is designed to be used on stock vehicles with no performance upgrades such as a cam, intake manifold, or carburetor.
Below 3,000 rpm, the MSD produces a series of sparks instead of just one. This ensures that the fuel is burned completely which in turn provides more power, smooth idle, quick starts and overall driveability improvements.

The MSD 5's powerful sparks are just the ticket to enhance the power of your foreign or domestic car's ignition output. The MSD 5 can be triggered using points or the electronic amplifier on late model vehicles.

NOTE: Not for use with magnetic pickup distributors or distributorless systems. Not recommended for General Motors HEI ignition systems.

Not knowing exactly how you have this all wired up, my suspicion is that you are tripping the coil with the MSD 5 unit, and therefore the tacho is getting "a series" of spark signals instead of just one per cylinder. This would explain the higher rev readings.

Assuming that the MSD 5 unit is triggered by the original distributor, I would say you just need to trigger the tacho from the original distributor signal, ie before the MSD 5 unit, instead of after it.

ps have you actually noticed a performance improvement with this thing?

pps are you sure your "sparky" is really a sparky?

[chimpboy]

Edit: looking at the wiring description for the MSD 5 unit, at http://www.msdignition.com/pdf/5200_frm18162.pdf, I would say you are currently hooking your tacho to the ORANGE wire, and you should move it to the WHITE wire on the other side of the MSD 5 unit.

[ledgno1]

Thanks chimpboy,

I have already tried hooking it up to the orange, white and red wire - none of which provide the desired results :(

The unit has definately improved the car - it is smoother, pulls that bit better and starts alot quicker than before - it's a pretty cool looking thing to have under the bonnet also

I will try hooking the tacho up to the wire coming directly from the distributor, however the way in which it's been wired up it appears that it will still be the same point electrically so I don't think it'll solve the problem

My sparky has been in the game for a lot of years so trust his expertise, he is of the opinion that due to the multiple sparks the tacho just can't cope with the modified pulse. However the way I see it, unless the pulse can be picked up from somewhere not associated with the MSD I'm not going to get the tacho to behaive That or I need something that converts the pulse back to its base state....

Thanks again for the info though - I will try your suggestion

[chimpboy]

The tacho signal is usually picked up at the coil, but it's really just a signal from the points. So if you hook it up between the distributor and the MSD 5 unit it really should work... unless the MSD 5 unit somehow back feeds a signal as well... which would be a bit dumb.

The website does say "TACH ADAPTER The PN 8910 will be required for foreign vehicles with fuel injectors. Some Ford tachometers may also
require the PN 8910 to operate. Figure 7 shows the installation of the PN 8910."

http://www.shopatron.com/product/produc ... 8910/424.0

But the only way the tacho won't work connected directly to the distributor, before the MSD 5 unit, is if the MSD 5 sends some kind of feedback as mentioned above. This seems really unlikely to me but if it is the case, a plain old diode after the tacho but before the MSD 5 should be enough to fix it.

[ledgno1]

Thanks again for the info chimpboy

I will definately try connecting the tacho wire direct to the signal wire coming from the distributor.

When you mention using a diode after the tach but before the MSD - where do you mean to locate it, and what capacity diode do you reckon to use??

I found this which also suggests a tach adaptor may be needed if the above fails:

http://www.msdignition.com/pdf/tech%20b ... top_10.pdf

I'll see how I go.....

Cheers