Lotus Elan

Tach, coil, Powerspark wiring

PostPost by: groucho » Mon Aug 09, 2021 1:42 pm

Just to give an update for this...

So with the wiring now sorted out, the tach still does nothing. But I think the sense part is working fine because when we connect a timing light and pull +12V from the coil (since it's the most convenient spot), the tach jumps up and bounces around the redline at idle and maxes out when there are any higher revs.

So, I've given up and ordered a Spiyda kit which I expect will work fine. We did get accurate RPM readings on my engine builder's fancy timing light that includes a tach.
Jeff Kyle
1965 Elan S2
2005 Elise
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PostPost by: mbell » Mon Aug 09, 2021 6:20 pm

groucho wrote:I'm wondering if I fried the electronic ignition when I was testing things.


I think they don't like to be left powered up but the engine not running. probably overheat due to constant current flow.

If you left ignition on and the module powered up it may well have failed. If i am leaving my ignition on but car not running for any time i remove power from the coil and electronic ignition module.
'73 +2 130/5 RHD, now on the road and very slowly rolling though a "restoration"
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PostPost by: groucho » Mon Aug 09, 2021 6:27 pm

mbell wrote:
groucho wrote:I think they don't like to be left powered up but the engine not running. probably overheat due to constant current flow.

If you left ignition on and the module powered up it may well have failed. If i am leaving my ignition on but car not running for any time i remove power from the coil and electronic ignition module.

Well, in testing, at one point I connected the white wire to the negative side of the coil. I would assume that fried it since I had no spark ever again with that module. I tested with my old points distributor and verified I could get spark then, and replaced the Powerspark ignition module with an extra one from another local Elan owner, and so I was back to having spark.

All my other wiring is all sorted now (I built a custom loom completely from scratch) so I don't expect to be leaving it with power on but not running for any significant time in the future, and I do have a quick disconnect on the battery and remove all power when I'm not using it.
Jeff Kyle
1965 Elan S2
2005 Elise
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PostPost by: groucho » Wed Aug 18, 2021 8:49 pm

Yet another update, probably truly the last this time, for the historical record!

So before using the Spiyda to convert to RVC, I decided to rewind the white wire around the sensing bracket in the opposite direction - and what do you know, the tach works! There's even not too much bounce; a little if you quickly rev it but generally pretty steady. The problem is that it reads about 1k RPMs too high.

I'm sure that it would be possible to calibrate it and/or replace any failing capacitors to get it reading properly again, but since the Spiyda arrived in my hands today, I will just go ahead and install it. But for the record, the stock RVI tach can work with a Powerspark (and presumably other electronic) ignitions.
Jeff Kyle
1965 Elan S2
2005 Elise
groucho
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Posts: 103
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Location: Rochester, NY, USA

PostPost by: JeffP » Thu Sep 16, 2021 12:24 am

Is my interpretation of this discussion correct?? I have a 69 Elan Plus2.

To get a Pertronix Ignitor II to work I will need to:

1. Modify the tach with a new board

or 2 Provide a separate power feed from the ignition switch or fuse box to the +ve on the coil and thence to the +ve lead on the ignitor module?

Please clarify.
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PostPost by: mbell » Thu Sep 16, 2021 2:30 am

The pertronix will work if wired as suggested by pertronix. I.e negative and positive connections to the coil.

It may however cause your tach to over read. The solution to that is either connect pertronix 12v supply not via the coil power feed from the tacho or convert the tacho.
'73 +2 130/5 RHD, now on the road and very slowly rolling though a "restoration"
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