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V-8 Engine Tech

electronic ignition

Mopar Big Block Talk

by currywurstcarpaccio » Wed Feb 05, 2020 8:49 pm

This all makes sense.
But I'm not sure if I can install the HEI correctly. The Pertronix systems seems to be very simple to install. I don't have enough knowledge in ignition systems so I'd like to go the easy way.
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by currywurstcarpaccio » Thu Feb 06, 2020 4:51 pm

I've changed my mind :D

Today I've bought an MSD street fire CDI with a matching coil. After reading the installation instructions there is one question. The MSD ignition box has to be connected to the distributor wires. I've no idea which one of the wires is positive or negative. The colors of the distributor wires in the instructions (black and orange) don't match with the colors of my distributor (brown-white and white-brown).

Anybody know which wire of the Jensen distributor is positive?

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by Philip Lochner » Thu Feb 06, 2020 6:32 pm

I don't know which is positive.

Nothing will break if you connect wrong way round. I suspect both ways may run, but the correct way will run better, with a more stable position of the timing mark.

So, just connect and turn the key. If she's not happy, swop and try again.

What is VERY IMPORTANT are those two thick wires. They REALLY need to be connected directly to the battery with equally thick wires.

Awaiting the outcome!
Best regards
Philip
Mk3 7.2 #128/8120 Jan 73 http://tinyurl.com/hsjucm5
Mk3 7.2 #2240.9677 May '74 modified:
Fuel injected: http://tinyurl.com/qyrx93f
GM 4L60e 4-sp transmission: http://tinyurl.com/qxlwk95
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by currywurstcarpaccio » Fri Feb 07, 2020 7:20 pm

Hi Philip, I've installed the MSD Street Fire today. There where no problems due to the good instructions. The wires from the distributor were easy to identify (black-white = negative and brown-white = positive).

Very big surprise came during the first test: the engine ran without any problems. Without exaggeration: Really at the first turn! Couldn't takte her out for a test drive but really impressing smooth running.

The only problem is a non working rev counter. Did anybody tried an adaptor that MSD offers?

Thank you very much, Philip for you helpful advices :D

Kind regards
Ralf

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by Philip Lochner » Fri Feb 07, 2020 8:06 pm

currywurstcarpaccio wrote:Very big surprise came during the first test: the engine ran without any problems. Without exaggeration: Really at the first turn!

The only problem is a non working rev counter. Did anybody tried an adaptor that MSD offers?
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That's excellent news Ralf!! Really glad that it has worked out well. Much of the performance you experience is due to the concept of multiple sparks per combustion stroke. With the spark plug positioned in "a corner" of the combustion chamber, it seems sensible to have more than one spark per combustion stroke - a kind of backup mechanism in case the first spark was not successful in igniting the fuel/air mixture. I forgot the detail but I believe at idle, each cylinder gets 3 (THREE) sparks on each combustion stroke up to about 1200RPM. Then it becomes 2 sparks per stroke and around 2400rpm, it becomes 1 spark as usual.

AS for the rev counter: Yep, that would be interesting. I don't have a straight answer for you.

The MSD has a tacho output, but that output are simply a series of 12V pulses and may be too small to trigger the rev counter. I got my OEM tacho working but I can't remember what I did. There might be something about that in my thread below on my EFI conversion. Did you try connecting this output to the tacho?

I all else fails I would simulate the coil- pulse from this tacho ouput by connecting it to a Bosch ignition module and using the coil of any automotive relay to generate the spike the tacho expects to receive as shown here http://www.megamanual.com/ms2/Bosch_124.htm
Best regards
Philip
Mk3 7.2 #128/8120 Jan 73 http://tinyurl.com/hsjucm5
Mk3 7.2 #2240.9677 May '74 modified:
Fuel injected: http://tinyurl.com/qyrx93f
GM 4L60e 4-sp transmission: http://tinyurl.com/qxlwk95
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by AndrewP » Sat Feb 08, 2020 2:46 am

Perhaps a silly Q, but have you made sure the white cable (negative from the tacho) is connected to the negative post of the coil.

I have a crane system in mine, but apart from the multi-spark all the system is doing is providing a precise low voltage on -- off to the standard coil. Cant see why the standard tacho wouldnt work (unless the MSD system doesnt switch to ground?).

Thinking aloud here as well...if you do get it to work, there may be issues with the multi-spark as Philip has mentioned below as rather than one on -- off per cylinder, per cycle....you could be getting 3...then 2....then 1?

Probably no help whatsoever...but food for thought maybe?
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by PeterHume » Sat Feb 08, 2020 10:03 am

Hi
I have an msd 6EFI ignition on my car. The tachometer works correctly using the tachometer output wire from the MSD box. The tachometer must NOT be connected to the coil terminals as the MSD box supplies much more than 12 volts to the coil. This high voltage will cook the tacho. I suspect your MSD is probably similar.
Regards Peter
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by AndrewP » Sat Feb 08, 2020 11:58 am

That doesnt make sense Peter.

12VDC (or thereabouts) battery, 12V system, 12V ignition coil, so cant work out how it can output higher voltage. It could convert the DC to AC, step up transformer and then rectify back to DC...I suppose anything is possible but given the coil is rated for a 12V system...surely any higher voltage would damage that as well (think using a non-ballasted feed supply to a ballasted coil).

Either way Ralf...if it works connecting to the tacho output..then theres the answer!
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by currywurstcarpaccio » Sat Feb 08, 2020 12:24 pm

You're right, Philip and Peter. There's a tacho output wire (grey) at the box and I've connected it to the tacho.
MSD says that the only wires that are connected to coil are from the box.

Maybe MSD's tach adaptor is the solution? From the website:

MSD Ignition Tach Adapter, Magnetic Trigger
Tach Adapter, Magnetic Trigger

If, after installing an MSD Ignition control, your tachometer, fuel pump relay or electronic fuel injection (in foreign vehicles) doesn’t operate correctly, your application may require a tach adapter. This is due to the trigger signal not being strong enough to trigger both the MSD and the factory’s components. Each adapter is simple to wire in and will have your MSD and vehicle firing away in no time! If you are using the magnetic pick-up input (green and violet wires) to trigger your MSD Ignition, you will need the PN 8920 tach adapter. The PN 8920 will correct the operation of most voltage-triggered tachometers that do not work directly off the tach output terminal of the MSD control. This adapter should also be used on current-triggered tach (hooked in series with the ignition switch).

Correct operation of voltage triggered tach
Use current trigger tach in line with ignition switch
Easy mounting and installation
Great for a mag pickup used to trigger MSD Ignition
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by Philip Lochner » Sat Feb 08, 2020 3:47 pm

Yep, it really looks like the tach adaptor is what is needed.

With the CDI MSD box, NOTHING else (NOTHING !!)must be connected to either coil+ or coil - unless you want everything connected to that wire to be fried proper.
Best regards
Philip
Mk3 7.2 #128/8120 Jan 73 http://tinyurl.com/hsjucm5
Mk3 7.2 #2240.9677 May '74 modified:
Fuel injected: http://tinyurl.com/qyrx93f
GM 4L60e 4-sp transmission: http://tinyurl.com/qxlwk95
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by Philip Lochner » Sat Feb 08, 2020 3:53 pm

This makes we wonder what the Pertronix Ignitor III would have done with tacho (which WOULD be connected to coil - ), since it would also generate more than 1 spark per combustion stroke... hmmmm....

Perhaps is best then to only consider using Ignitor II (when a points to electronic conversion is called for).
Best regards
Philip
Mk3 7.2 #128/8120 Jan 73 http://tinyurl.com/hsjucm5
Mk3 7.2 #2240.9677 May '74 modified:
Fuel injected: http://tinyurl.com/qyrx93f
GM 4L60e 4-sp transmission: http://tinyurl.com/qxlwk95
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by currywurstcarpaccio » Sat Feb 08, 2020 4:51 pm

Philip Lochner wrote:Yep, it really looks like the tach adaptor is what is needed.


Perfect ;-)
I ll keep you updated.

Ralf
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by currywurstcarpaccio » Fri Feb 14, 2020 6:10 pm

Now the tachometer works :D

But I didn't need the tach adapter, I only needed a ground wire. What a stupid mistake I made: I just forgot to attach the ground wire to the tacho :oops:
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