Ignition issue on my serie 3 1972

[Djerome60]

Hello everyone,

sine few weeks now, my serie 3 from 1972 (negative earth) with its original Opus system has no more spark while cranking (will come back to that later)
I have done some tests and please see below my findings:
- Battery voltage is 12,7 volts
- When the ignition switch is on i have 3,7 V at the coil
- When cracking is goes to 4,5 v
- when i stop crancking is suddently goes to 6/7 volts for few 1/10 secondes (sometimes the engine starts)
- I have changed the coil - no change
- I have remove the distributor head and it looks perfect
- the leads are new (2 years old) and seems ok

Going through the repair manual it seems that the ballast resistor is faulty but before buying a new one i wanted to get you thoughts.

I do not want to polute too much this post and therefore your feedback but before i face this issue my car was "sometimes" not running well and smooth for a while and i was suspecting a carburator issue and therefore i inpected them, clean them, ..... and it does improve the behavious until i faced this "spark" issue.

Thanks in advance
Regards
Jérôme

[MarekH]

With such a low voltage on the coil, what you seem to be telling us is that you are not charging the coil. That means there is too high a resistance in the path to/from the coil. The manual tells you what the resistances ought to be across the ballast connections and you can check these. I would check all of the connections along the path as that may add to the total resistance, making less voltage available to charge the coil with. There shouldn't be any voltage drop between the battery and the ballast. That path includes the ignition switch, the 22RA starter relay, wiring and various bullet and spade connectors.

kind regards
Marek

[Djerome60]

Hi Marek,

thanks for your feeback.
I found a slot yesterday night to make further tests:
-I tested the resistor ballast as per manual and all resistances are within specification
- I checked/cleaned all connections and i found out that one connection on the ballast resistor was suspicious.
.Then i checked again the voltage at the coil and i have now 4,5V with ignition switch on, almost no change while crancking and goes to 6V for few 1/10 sec when i stop cranking.

Can you please give me the procedure to test the ignition switch and the 22RA relay?
Or do you have any other potential root causer to look at?

Thanks
Regards
Jérôme

[MarekH]

Firstly you should download the wiring diagram for your car and use it as a reference.

The blue Repair and Operations manual has the relevant tests listed. 86.35.29/2 states 4-6volts for the coil positive, so it suggests your wiring can still improve, as you have gone from 3.7 to 4.5v. The ignition amplifier tests are at 86.35.29/4 onwards.

To test the relay and ignition switch:-

Unplug the ignition switch. When turned to position #2, there should be zero resistance between the brown wire input and the white wire output. When turned further to spring-loaded position #3, there should be zero resistance between brown wire input and both the white wire and white/yellow wire outputs. Reconnect the ignition switch.

For the 22RA, disconnect the battery. Apply a PP3 battery across the 22RA's w1 and w2 terminals. You should hear a click and there should be zero resistance between c2 and the c1/c4 terminals. Reconnect the wiring as per the wiring diagram and reconnect the battery.

For the wiring and wiring connectors, there are two methods to check integrity.
1/ You can leave the battery connected and measure what the voltage drop is along the path from the battery positive to the component being tested. There should be no voltage drops along the path. Similarly, there should be no voltage registering between the battery negative and any earth connection of the component being tested.
2/ With the battery disconnected, you can do similar tests but measure resistance along those paths instead. There should be zero resistance.


Resistances below around 2-3ohms are very difficult to measure. Even though a meter may register to within 0.1ohm accuracy, it doesn't mean it is accurate. A more reliable method is to light a curcuit up with some load, measure the series current flowing and then measure the voltage drop across part of the path of interest. Use Ohms law to work out the resistance. This works better because voltage measurements are more accurate than trying to ascertain the value of a resistance which is probably the same size as the wiring of the meter leads themselves.

kind regards
Marek

[Djerome60]

Thanks Again Marek four great support.

Sorry for not getting back earlier. After performing all tests the amplifier i found out the amplifier was faulty and therefore i took the oportunity to convert my OPUS system to the SNG Barrat conversion kit.
The car fired up immediately and run perfectly well.

The only issue i have left is tha tacho which does not work. I quiclky checked the signal connection to the ballast and seems ok.
Any advice on what i should look at?

Thanks
Best regards
Jérôme