Electrical Issue After Trying Rev Counter

[mjh1]

Hello all,

I have just tried wiring in my new (to me) Smiths RVI Tacho. I have points and so assumed all would be well but....

After the car running for about 5 mins it spluttered to a halt (rev counter seemed to work at 1k Revs but went down instead of up when I increased the revs.
Being concerned that the car had died I removed all the temp wiring but the car still fails to start. I did notice that the coil got quite warm so thought I may have cooked it. Tried with another coil and still the same result.

Any ideas please, I have +12v going to the coil and then the - terminal of the coil going to the Dizzy and I think that should be all that's required?

I do have a spark but it looks quite weak and it's not trying to start at all.....

TIA

[myoldjalopy]

Can we assume that the car was functioning perfectly before this gizmo was fitted?

[mjh1]

Sorry should have said, was running sweet prior.

[oliver90owner]

Please describe that weak spark. What gap, colour, how tested.

[mjh1]

Weak spark as in removed spark plug and grounded the bottom of the elclectrode on the car (mine is negative earth).
Spark looks weak and erratic.

[svenedin]

I really don't know what damage, if any, connecting up your tacho may have done. It could be coincidence but the fact your tacho went backwards suggests it was connected with the wires transposed (the wrong polarity).

The ignition system is very simple. You have tried a different coil (do you know the coil is good? Have you tested its resistance?). The spark seems weak and erratic. Check all the connections are good. King lead etc. Sometimes the king lead doesn't make a good connection when removed and replaced and it needs the metal connector inside the rubber insulating shroud bent out again a little. I don't know by what mechanism a condenser could be damaged but they are not expensive so why not try a new condenser? While you are there, clean and gap the points. Also check for pitting on the rotor, cracks, arcing burns and cracks in distributor cap.

Also check the condition and security of any connections you may have moved when you temporarily wired in your tacho. It's possible you put a connection back in the wrong place or just by disturbing the connection it is no longer a sound electrical connection. Clean up the blade of any suspect connection with fine emery paper and ensure the spade is tight.

Stephen

[mjh1]

Hello Svendin,
there are no security systems on the car but a quite a lot of dodgy wiring!
I know what you mean about the King/HT lead and I did actually try what you said and bent it out a little for a better fit into the coil. I also tried to sand the points connection. 1 thing I have noticed is that when the ignition is on, the the distributor cap removed I do not got any sparking when opening and closing the points which I would expect?
I do get a spark if I short the points out with my screwdriver so I'm now thinking points?
Could I have damaged to points somehow?

[geoberni]

Yes, you're right, ish, there should be a minute spark at the points, but of course you'd need to have it pretty dark to see it. The Condenser is there to stop sparks.

However, you've said that you're getting a Spark at the Plugs, albeit a smaller one than you'd expect, so the points must be working.
You can't get a Spark at the Plug unless the points are working....
Watch this short video to understand the relationship between Points, Coil and Condenser.

https://youtu.be/lWyn_eV-DzM

[mjh1]

Hi geoberni,
thanks for the video, it was very informative especially about the condensor. I've tried again to look tonight but still not working.
What about bypassing the loom any running +12v to the + side of the coil and running the - side of the coil to earth/negative o the battery terminals.

IS there anything in the Dizzy I could have damaged?

[myoldjalopy]

No, don't wire the coil up like that, it will just burn the coil out!

[mjh1]

So, after reading up a little my next focus will be on the condensor.
My car has an external condensor (located near the coil). Question is it it possible to test it with a multi meter and I think it should be connected to the - (negative) Coil terminal?

[svenedin]

So, after reading up a little my next focus will be on the condensor.
My car has an external condensor (located near the coil). Question is it it possible to test it with a multi meter and I think it should be connected to the - (negative) Coil terminal?

External condenser? Are you sure it’s not a ballast resistor? Post a photo if you can.

Stephen

[StillGotMy1stCar]

So, after reading up a little my next focus will be on the condensor.
My car has an external condensor (located near the coil). Question is it it possible to test it with a multi meter and I think it should be connected to the - (negative) Coil terminal?

It could be a Suppression capacitor if it is connected to the ignition supply side of the coil and bolted to the coil bracket, it should have a value of around 1uF.
It is to help stop interference on AM radios.
A photo would confirm.

Regards John

[mjh1]

Hi all, many thanks for all the help so far...
Please see the pics..

[myoldjalopy]

So you have a condensor in the coil, which is normal, and one wired into the coil as well. That is not unheard of and, in fact, I have one wired into my coil as well. And one wired up to the petrol pump. Whether this makes any difference, I don't know - it wasn't me that fitted them but an old-time mechanic many years ago so he obviously thought it a good idea.

[mjh1]

So nothing there that would stop it running.
I think I'd better take a look at the fueling next then. As I say, been running fine but suddenly stopped when I was messing about. Coincidence maybe?

[oliver90owner]

Start with the king lead held close to the engine block/head (with a 6-9mm air gap). With the supply to the coil on, momentarily connect the dizzy-side coil terminal to earth (to provide a current through the coil). Switching the supply should generate a healthy spark at the king lead to engine gap. If the spark is a good healthy one, the coil is working (at least while cold). If not the coil is dead.

Simple enough as a first check? Go from there with other checks as necessary.

[mjh1]

Thanks very much, I'll try that in an hour or so and post the results.
I have tried with a known good coil from another car though but would like to confirm this is happening.

[mjh1]

So, as you suggested there is a healthy spark from the HT lead, so that's the coil eliminated.

[mjh1]

...and with the Dizzy connected to the - on the coil, I measure 1v at the - terminal.
Without the dizzy connected I measure 12v at the same - terminal on the coil.