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MG MGB GT V8 Factory Originals Technical - Ignition
While attempting to fix a faulty connection on my distrubutor today (early Rover P5B fitted with a Lumenition module) I fear I may have inadvertently dmaged the control unit.
The Lumenition control unit is a small cast aluminium box wiith three or four wire running from it. Some of these wires shorted out against the live feed to the alternator, causing a few sparks. Anyway the net result is no ignition.
Having said all that, my question concerns a Lucas SD1 distributor that I have - 35DE8. This has two wires coming from it, one red/black and one white/black. Does anyone know how these should be connected up? Did this distributor require an external module (which I don't have)? The internals of the distributor contain a hall type sensor, transistor etc., so it looks fairly self-contained to me.
Any ideas, let me know.
|The MGB 45DE had an integral module and hence was self-contained, but the integral module was a big lump on the side and had three wires coming out of it. The 45DM4 used an external module and only had two wires coming out of it, the module has four wires. The factory V8 only ever used conventional points. White/black on an MGB is the wire that goes between points and coil and tach i.e. the output wire. It's possible that your red/black wire is the 12v feed to the electronics inside the distributor, and it is self-contained as you say. I may be able to get more info later.|
|The 35DE8 distributor has an external ballast resistor pack that is normally mounted adjacent to the ignition coil. If I remember correctly it contains 5 resistive elements in an aluminium heatsink.|
The cable out of the distributor should terminate in a flat white three way plug flying leads about 10 inches long to connect to the coil, one from the white/black wire and one from the third way on the plug. This plug connects to one end of the resistor pack and a similar one connects to the other end with connections to the tachometer, the ignition and the starter feed.
This system is the Lucas 'Opus' - often called the hopeless ( silent H ) because its supposed to suffer from high speed misfire problems especially in a hot engine bay. I used one without problem for five years including racing, although I now use a lumention optical system I'd still be on the old opus if I'd found the bad cable connection earlier!
Hope this is helpfull, I can probably find the resistor pack values given a little time.
I attempted to run with the original hei distributor also when I did my V8 conversion but to no succes. I then installed a Lumenition system in the original distributor. You will have to cut out all the internal transistors etc from the old hei system and install the infrared sensor. The system works very well altough I had a sensor failure after a couple of months. I got now a spare set in the car! My best bet is to write to Lumenition and send the unit back so they can check it out or find the NZ dealer to help you with that. Sofar I like the lumenition system. Holds up good in very high heat!
|werner van clapdurp|
|I have used the Lumenition system on three V8s to date without a problem and on many other cars as well. I highly recommend them!|
I agree the Lumenition system is good, however, I managed to wreck mine while attempting to improve the connections on it (if it 'aint broke...). A couple of the wires touched the feed to altenator and shorted out. I've tested the system using a Lumenition book lent to me by a local dealer and it's broken.
However, I do have a 35DE8 distributor (Opus type from an SD1) that I'd like to use instead. So my question is, does anyone know how to wire this up in a non-SD1 application? There are two wires coming from the distributor, one black/wite and one red/black. In the SD1 these are connected somehow to an external resistor pack (that I don't have).
Any idea how this is connected up in relation to the coil - I use a non-balast resistor type coil?
|Simon, Dave Brooke has answered all your questions. But you will need a ballast type coil. Barrie E|
|Why the ballast-type (6v) coil? Isn't a 12v coil electrically the same as a 6v coil plus ballast? If you do fit a 6v coil in place of a 12v you will have fit the ballast as well, and that is resistance wire contained within the loom.|
|The ballast coil is for easier starting. In "start" mode, the resistor is bypassed so the 6v coil gets 12v for starting. In this case,a ballast coil is needed to make it compatible with the resistor pack that has to be used with this type of distributor.Barrie E|
|I know about the 12v to a 6v coil during cranking, that is the same for a points system. My question was "why do you need the ballast-type coil for the 35DE?". Are you sure the 35DE uses the same ballast for both coil and distributor? The 45DE Opus system uses separate ballasts.|
From the wiring arrangements for the Opus set up I feel that the feeds to the coil and dizzy are different.
|I think so to, which is why I think the Opus will work with either system, even though it was probably originally used with a 6v coil with external ballast. The important thing is that if Simon chooses to use the 35DE he will have to install the distributor ballast, and if he opts to fit a 6v coil he will have to install coil ballast as well.|
Roger sent me a good sketch of how to connect up the 35DE8 Opus distributor. I'll have a look at it tomorrow.
As my coil is a non-ballast type I'll feed 12v straight to it.
I don't have the resistor block that is used with this distributor, does anyone know what value resistor should be used in the 12v feed to the red/black wire on the dizzy?
What is the purpose of this resistor - do I need it?
Thanks to everyone who replied for their help.
|There is a diagram of how the Opus *45DE4* is wired (colours are different, though) on the above web site - select 'Spanners', 'Electrics', 'Schematics' and 'Ignition', then scroll down to 'Early Electronic Ignition'. Don't know what value the distributor resistance is but I would imagine it is essential.|
Another person (Nigel Rotheram) has kindly sent me some scans from a Lucas service book, so I now have the values of the resistor pack for the 35DE8.
The 12v +ve feed to the dizzy (red/black wire) has a 0.5 ohm resistor in it. The coil is fed by a via 1.7 ohm resistor under normal conditions and via a .265 ohm resistor for starting.
Is the purpose of these resistors to limit the current used by the dizzy/coil?
Dredging up my A-level physics has not been much help, as I can't figure out how a 0.5 ohm resistor is going to do much for the dizzy.
My Bosch coil is a non-balast resistor type, although I unwittingly ran with a ballast resistor in series (in the wiring harness) for several years.....
Any electronics experts have an opinion?
|1.7ohms is about the resistance used for the external ballast (resistance wire contained within the loom) used with a 6v coil on a 12v system. This is usually shorted out during cranking by a special contact on the solenoid to give as much voltage to the coil as possible to aid starting. The 45DE4 doesn't use a .265ohm during cranking according to the info I have, but that is by-the-by. |
0.5ohms will have an appropriate effect according to system voltage and current drawn, the original designers obviously felt it was necessary.
Looks like you will need re-introduce the harness ballast for this system, and use a 6v coil otherwise you will be running on half-strength sparks.
This thread was discussed between 05/06/2000 and 13/06/2000
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