fellowes
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| posted on 8/9/06 at 01:27 AM |
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Megajolt Lite Jr and Tach
I've got the megajolt light jr hooked up and running on my zetec 2.0L engine. This is the Ve with TPS. However, when I try to hook up my
Smith's impulse style of tach to the wiring diagram at http://picasso.org/mjlj/?q=node/2 (see the bottom of the sheet) the engine will no longer
run. Any thoughts? I've tried reversing the zener diode to no effect
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Danozeman
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| posted on 8/9/06 at 05:30 AM |
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Sounds like its earthing the coils out somehow. Are u sure your connecting to the right terminal on the tacho?
Dan
Built the purple peril!! Let the modifications begin!!
http://www.eastangliankitcars.co.uk
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fellowes
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| posted on 9/9/06 at 01:37 PM |
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There is a 12v wire from the ignition switch that runs to the tach.....and goes around an inductor inside the tach.....and then comes out. This is
the wire that went to the ignition coil on my distributor fired BMC engine. I replace the engine with the Zetec....and then hooked up the diodes and
zener diode per the diagram....and then connected the zener to the original wire that ran from the tach to the old ignition coil. When the ignition
switch is on.....the wire from the tach registers 12v. I disconnected the zener diode and left the other two diodes in place....and the engine ran
fine. BTW...it is the V3 version of Megajolt. Any thoughts?
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paulf
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| posted on 9/9/06 at 09:14 PM |
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It probably would have worked by connecting it in the feed to the coilpack as per the original connection to ignition coil.
I have one of these tachos and have often wondered if it would operate wired into the coil feed so may try it.
The diode arrangement is normally used to give the higher voltage signal required by some older tachos.
Paul.
quote:
Originally posted by fellowes
There is a 12v wire from the ignition switch that runs to the tach.....and goes around an inductor inside the tach.....and then comes out. This is
the wire that went to the ignition coil on my distributor fired BMC engine. I replace the engine with the Zetec....and then hooked up the diodes and
zener diode per the diagram....and then connected the zener to the original wire that ran from the tach to the old ignition coil. When the ignition
switch is on.....the wire from the tach registers 12v. I disconnected the zener diode and left the other two diodes in place....and the engine ran
fine. BTW...it is the V3 version of Megajolt. Any thoughts?
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fellowes
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| posted on 10/9/06 at 01:16 AM |
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Just came across an article on the web....that highlighted there were two types of Smiths tach. One driven by current (RVI type)....and one driven by
voltage (RVC type). The article went on and said that the RVI type will not be able to work with electronic ignition. Guess what? I had the RVI
type. Switched it to a RVC type and the car starts. The tach might not be good though....as it was reading 60% less on rpm. Will try and find
another RVC tach and see it I can now get the correct rpm
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MikeRJ
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| posted on 10/9/06 at 01:28 PM |
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quote:
Originally posted by fellowes
Just came across an article on the web....that highlighted there were two types of Smiths tach. One driven by current (RVI type)....and one driven by
voltage (RVC type).
As Paul suggested, try using your current driven tacho (RVI type) via the coil positive connection, as it was intended to work. There's a
chance that it will work with the megjolt system as it will see the correct number of pulses.
The problems with these old tachos is that a) they are old and the components drift with age
b) they are very crude, and can be affected by the igntion waveform shape. Obviously a low impedance electronic system has a very different waveform
to an old points driven system.
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