Lotus Elan

Ignition- No Spark at Plugs

PostPost by: EwanG » Tue May 30, 2023 8:09 pm

Hi All,
I am still in the very early stages of my late 1968 Lotus Elan Plus 2 restoration (#50:1154) and am generally making some good progress. Some key parts were missing but mostly seems original

I'm now turning the key for the first time after renewing the fuel pump, servicing the starter motor, servicing the Webers, new plugs, points, distributor cap, leads, fuel tank, and exhaust.

New battery installed (negative earth), with good connections, and I am getting a 12 volt plus reading at the starter solenoid. She has also been fitted with an alternator at some stage.

The engine is turning over nicely but I am not getting a spark at any of the plugs. I have a 12v coil (non ballast that has two wires connected:

1. Red/Green from loom to negative terminal
2. Black from Distributor to positive terminal

Q1. Are these wires connected with the right polarity? Does it make a difference?

I have tested the coil with a multi meter and getting the following readings:

1. 9.96v to the negative terminal (RG wire) when ignition is turned on (not cranking)
2. 3.5ohms resistance on the primary coil
3. 6900 ohms resistance on the secondary coil

Q2. Do these readings sound ok? (They do to me but I'm still learning!)

Q3 . If both of the above are ok, what next? Is there something else to test at the coil or the distributor that would help?

Thanks!
Lotus Elan Plus 2 1968 (Restoration - off road since 1980)
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PostPost by: ericbushby » Tue May 30, 2023 8:33 pm

Hi Ewan.
I have found that a good test to do is to make up a short piece of stiff wire to push into the coil high voltage output socket. Bend it round until you have a spark gap to the coil body.
This will tell you if the problem is before or after that point. As is usual with testing, try to divide the system into two parts. It is no use suspecting the ignition system until you know there is a spark to begin with.
You do not mention the rotor arm which is a notorious failure point.
Good luck
Eric in Burnley
1967 S3SE DHC
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PostPost by: EwanG » Tue May 30, 2023 8:56 pm

Many thanks Eric. Good point re rotor arm - I changed the condenser but forgot to order the rotor arm, crossed my fingers, and then forgot all about it. I really should order one - even if it becomes a spare.

Can you please reword "bend it round until you have a spark gap to the coil body" as I don't quite understand that bit? Would that be when ignition on only or when cranking?

Thanks
Lotus Elan Plus 2 1968 (Restoration - off road since 1980)
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PostPost by: ericbushby » Tue May 30, 2023 10:27 pm

Sorry, I will try again.
Firstly the coil gives out a high voltage sufficient to produce a spark across an air gap of 30 thou` in a pressurised cylinder. This is equivalent to a much larger gap in normal air pressure. This voltage is applied to the spark plug and it sparks to earth (ground).
So if you make a temporary circuit from the coil output to earth with a suitable gap in it a spark will occur across the gap.
This removes all the complications of the leads, distributor, rotor arm and plugs.
From the coil there is an HT lead to the centre connection of the distributor. Remove this lead from the coil and set up a temporary circuit from the coil output to ground which has a small gap in it. If everything is working up to that point then when you crank the engine a spark will occur at the gap. The nearest ground connection is the body of the coil itself. I just used a bit if stiff wire pushed into the coil output terminal and bent round to nearly touch the coil body.
If you feel a bit twitchy about making a spark in that area then form a barrier between the coil and the carburettors, just a piece of plastic or cardboard should do it,
If you see a satisfactory spark from the coil when cranking then you can start looking at the ignition system downstream-- lead from coil to distributor, distributor, rotor arm, plug leads and plugs.
Let us know how you get on,
Eric in Burnley
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PostPost by: EwanG » Tue May 30, 2023 10:38 pm

Thanks Eric. That all makes perfect sense - thanks for re-explaining and I will definitely let you know how I get on. A good tip too re forming a barrier between the coil and the carbs - one benefit of my last 3-4 cranks is that I know that the new fuel pump is primed and getting fuel to the carbs (a lovely smell of fresh fuel!)
Lotus Elan Plus 2 1968 (Restoration - off road since 1980)
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PostPost by: EwanG » Thu Jun 01, 2023 6:37 pm

Based on Eric's advice I have now tested setting up a temporary circuit from the coil output (HT) to ground with a small gap. When I crank the engine there is no spark. I tried 2-3 times with different wires and grounds with the same result. Does that mean that the coil is the likely culprit given that I have already tested the coil with a multi meter and getting a reading of 9.96v to the negative coil terminal (RG wire) when ignition is turned on (not cranking)? Or do I need to look elsewhere first?

Thanks!
Lotus Elan Plus 2 1968 (Restoration - off road since 1980)
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PostPost by: Craven » Thu Jun 01, 2023 7:04 pm

If you can turn the engine over by hand or very slowly you can check the operation of the contact breaker circuit by monitoring the voltage between the neg terminal on the coil and earth that the coil terminal connected to the distributor, voltage will change from your 9.9 volts and zero. If it stays high then check points gap for good contact or if stays low zero then points contacts are permanently closed or you may have assembled the contact breakers incorrectly a common mistake here is the wire connection is on the wrong side of the insulator on the spring contact.
May help.
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PostPost by: ericbushby » Thu Jun 01, 2023 7:20 pm

Well done Ewan,
You now know that the trouble is probably upstream of that point.
It is a well used method of fault finding to divide the problem into two halves without testing individual components. You can now do it again with the suspect area until you have the faulty item surrounded.
I do not know enough about Plus 2 wiring so I will step back now and see if the plus 2 owners can help.
Cheers
Eric
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PostPost by: EwanG » Thu Jun 01, 2023 7:49 pm

Thanks Eric - a great learning experience - thanks again.

And thanks Craven, I will give that a go as my next activity. I replaced the points and condenser a few ago when I replaced the Distributor cap and leads and remember I had a minor struggle getting the slightly different thickness of connector to fit and may have messed up the insulator on the spring contact at that point! Of course, it was easier when I had the carbs off but hey ho the joys of the Elan :D
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PostPost by: EwanG » Fri Jun 02, 2023 7:16 pm

I can happily report that I now have sparks at the plugs. I removed the points and examined the insulator washers and compared it with a diagram I found online. In summary I think I only had one at the bottom and was missing the one on the top. I robbed one off the bottom of the old set of points and re-used. When I turned the crank manually with the ignition on and monitored the voltage on the other terminal on the coil things had changed for the better. Upon reassembly I now have strong sparks at the plugs.

Thanks to Eric and Craven for helping me complete the right diagnostics!

Tomorrow I will head back to see if she will actually start now but time now for a beer :D
Lotus Elan Plus 2 1968 (Restoration - off road since 1980)
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PostPost by: ericbushby » Fri Jun 02, 2023 7:28 pm

Sounds like a result to me.
Eric
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PostPost by: Craven » Sat Jun 03, 2023 10:12 am

Well done, all we need now is the spark in the right place at the right time! Lots on here about Static Timing.
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