Scimba - Back in the game

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Re: Scimba - Back on form

Post by philhoward » Wed May 31, 2017 1:43 pm

When it's running you'll only see an average.

If when static you get about 9V, then that's about 3/4 of the battery voltage.

When running, you should have about 13.5V

Duty cycle of the points is probably only about 50%?

A quick calc says you'll get about 87.5% of available voltage in that case which is 11.8V or so.

If your alternator is in fine fettle and the ballast resistor drops the coil voltage to a nominal 10V (engine off, ignition on), then you could see as much as 12.5-12.8V.

As long as it's lower than battery voltage by a couple of volts, it's fine *when running*


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Re: Scimba - Back on form

Post by Crowther » Wed May 31, 2017 4:40 pm

An excellent explanation. Thanks for that. But back to the drawing board for me...


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Re: Scimba - Back on form

Post by Crowther » Wed May 31, 2017 5:47 pm

Now that I know the ballast wire is definitely there I suspect I shouldn't be feeding the electronic ignition module from the coil positive feed. I need to find a suitable 12V source.
I still don't understand why the car runs so well for 30 minutes or so and then gives up the ghost.


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Re: Scimba - Back on form

Post by DARK STAR » Wed May 31, 2017 5:49 pm

By-pass it, fit a 12v coil and stop worrying about the problem!
Neither of my cars has a ballast resistor or eureka wire ...


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Re: Scimba - Back on form

Post by Crowther » Wed May 31, 2017 6:24 pm

Stopping worrying is the main goal! How easy is it to bypass the eureka wire? I do want to get it sorted one way or another. I can't be limited to 30 minute journeys!


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Re: Scimba - Back on form

Post by DARK STAR » Wed May 31, 2017 6:46 pm

There are those that will tell you that if you just replace it with a bit of normal wire, the dashboard gauges will be affected as they need a stable 10v supply.
My gauges all work normally so either I'm lucky (for once/twice) or they are wrong ...


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Re: Scimba - Back on form

Post by scimjim » Wed May 31, 2017 7:20 pm

The fuel & water temp gauges (the only ones that get a 10v supply from the voltage stabiliser) have nothing to do with the eureka wire which runs from the tacho to the coil.


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Re: Scimba - Back on form

Post by DARK STAR » Wed May 31, 2017 9:58 pm

Ah, ok - I'm getting confused again, so some cars have a ballast resistor (voltage stabiliser) AND a eureka wire?
And in the case of the eureka wire, bypassing it and changing the coil should be the perfect solution?
Why do 9 volt coils exist?


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Re: Scimba - Back on form

Post by philhoward » Wed May 31, 2017 10:08 pm

Chris,

Ballast resistor OR Eureka wire - used on the ignition coil feed.

Voltage Stabiliser - generates a 10V (average) voltage for use with gauges.

Not to be confused with each other especially as your Coupe has neither although your GTC has both :mrgreen:

Tony Idle did a very good write up on ballasted coils etc for Slice I think?


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Re: Scimba - Back on form

Post by Crowther » Wed May 31, 2017 10:41 pm

Right, a quick recap.
Judging from the multimeter test and Phil's sums I have a eureka wire, which makes sense for a 5a.
The coil is a 9V coil - Lucas DLB102.
There is a Powerspark ignition module in the dizzy. Its +ve feed comes from the coil.
All of this results in a car that starts on the button and runs well... for about 30 minutes, so I'm thinking heat is a factor.
The coil was bolted to the engine block and I've temporarily moved it to the spare wheel tray but I haven't had a chance to try it out on a good run. I also want to add an earth between the distributor's top plate and body. After that I'll try finding an ignition switched 12V feed for the Powerspark. After that I'll be out of ideas. I'd try putting it back on points but I don't have all the tiny screws and insulating washers for it.


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Re: Scimba - Back on form

Post by scimjim » Wed May 31, 2017 10:58 pm

It could be the powerspark having problems with only getting 9v but I would have thought that would give difficult starting and problems at high RPM? Worth feeding from 12v just to be sure but I'd also consider removing it altogether and temporarily fitting normal points, just to confirm its not at fault?


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1300 SS1 (Number One) & Sarah's coupe.
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Re: Scimba - Back on form

Post by Crowther » Wed May 31, 2017 11:44 pm

Jim, as always you are right. I'm going to put it on points. Does anyone know where I can get all the tiny screws and washers for a motorcraft dizzy?


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Re: Scimba - Back on form

Post by DARK STAR » Thu Jun 01, 2017 6:04 am

Oh well, I'll have to study the wiring diagram when I have time.
My GTC has a 12v coil and definitely no eureka wire or ballast resistor, what does a voltage stabiliser look like?
My car also doesn't have a petrol return to the fuel tank, which apparently they 'all' have (Pierburg carb) 8)


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Re: Scimba - Back on form

Post by scimjim » Thu Jun 01, 2017 6:46 am

Eureka wire on the C is in the loom between the duraspark and coil (QRG sell the NOS complete loom and I bought one for my C but it turned out to be a failing duraspark module). Terminology is a little confusing because what we call a 9v cool is often called a 12v coil with a primary resistance of 1.5 ohm - for example the standard Lucas DLB102


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Current: SE5 (8Ball), TI SS1 (snotty), 1600 SS1 (G97), 1600 SS1 (C686CCR), 2.5TD SE5a (diesel 5a), 6 x random other SS1s.
Previous: SE5, 3 x SE5a, 2 x SE6a, 3 x SE6b, GTC, 2.9i GTC, 3 x 1600 SS1, 1300 SS1, Mk1 Ti Sabre, Mk1.5 CVH Sabre
Chief mechanic for: 1400 K series SS1 (Megan3), 1400 CVH EFi SS1 (Grawpy), Sabre/MX5 auto (The Flying Broomstick),
1300 SS1 (Number One) & Sarah's coupe.
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Re: Scimba - Back on form

Post by Crowther » Thu Jun 08, 2017 8:33 pm

Another test drive. Fine for 20 mins. Undriveable after 40. Tacho drops to zero when the throttle is closed. Backfires on deceleration, bogs down on acceleration. I came home, hacked off, decided to check the inlet manifold bolts and managed to snap one off having misread the torque figures. So that's great.


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