Weak spark from ignition coil. (Estelle 105/120)

[Rusty105L]

Hello,

I’ve tried to get my ’81 105L to run, and I’m unsure where to go next.

 

Here’s the deal:

When I bought the car 2 years ago the red wire from the ignition coil was badly melted, as in the insulation began shedding off the copper conductor. I sheepishly thought that it would be an easy project to just replace the wire and get it up and running as the car allegedly was running fine before this. What I assume happened (I forgot to ask the seller) is that the previous owner overloaded the wire by connecting an aftermarket electrical fuel pump to the positive end of the ignition coil. (I have since ditched it and rebuilt the original pump.)

However, after replacing multitudes of ignition-related parts I’m running out of ideas. The coil is getting around 7V when the ignition is on and 8.9V with brief spikes up to ca. 10V even when the battery is fully charged. Is this enough to make a proper spark? The coil has a resistor on it, but isn’t the voltage a bit too low? I measured the resistance on my replacement wire and it’s only a few ohms. I should also note that the other wires in the loom have no visible damages. There may be a few weak sparks when cranking the engine for a while whilst holding the HV lead near the block.

 

 

Ignition-related parts I’ve replaced with new ones:

-Ignition coil

-Distributor cap

-Sparkplugs

-HV-leads

-Distributor capacitor

-Positive lead from starter motor contactor(?) to coil.

-Distributor rotor

-I’ve also polished the battery terminals and ignition connectors on the coil and starter.

 

I’ve been told to remove the voltage regulator and run the car without it. I’m skeptical though, since it’s there for a purpose, right? Also, could the ignition key-switch itself be the problem? 

I should also mention that the engine was swapped from the original 105L engine to a ’86 120GLS engine before my ownership.  I have the original engine lying around but it’s been seized for some time now.

 

All in all, I’m stumped… ☹

Thanks in advance for any suggestions on how to fix!

And please be kind, I’m new to this stuff. 😅

[KenONeill]

14 hours ago, Rusty105L said:

I’ve been told to remove the voltage regulator and run the car without it.

All that will do is give you excess voltage when the engine is revving. It would be quite possible for it to boil the battery, and cook any electronics the car has (for example a radio).

[J.R.]

You have a ballasted ignition coil, when the engine is running the voltage drop across the ballast resistor should drop the voltage to around 9v, that is just an off the cuff figure, it could well be 7v for your vehicle.

 

When the engine is cranking an additional contact on the starter solenoid will put full battery voltage direct to the coil to compensate for the volt drop from cranking.

 

If you have the correct coil and the correct ballast resistor (nobody has been swapping stuff around) and it is correctly wired then you can calculate the voltage you should be reading using Ohms law for the series circuit.

[J.R.]

You should check where that red wire goes to, it should be the starter solenoid and it should have 12v  (probably a bit less) on it only when the engine is cranking.

[Rusty105L]

7 hours ago, KenONeill said:

All that will do is give you excess voltage when the engine is revving. It would be quite possible for it to boil the battery, and cook any electronics the car has (for example a radio).

I suspected over-voltage would be a problem, thanks for confirming.

 

 

1 hour ago, J.R. said:

You have a ballasted ignition coil, when the engine is running the voltage drop across the ballast resistor should drop the voltage to around 9v, that is just an off the cuff figure, it could well be 7v for your vehicle.

 

When the engine is cranking an additional contact on the starter solenoid will put full battery voltage direct to the coil to compensate for the volt drop from cranking.

Alright, so by the sound of it there's some significant voltage drop on my system? Do you know what to do to address this? Could it be the capacitor that's affecting this?

 

 

1 hour ago, J.R. said:

If you have the correct coil and the correct ballast resistor (nobody has been swapping stuff around) and it is correctly wired then you can calculate the voltage you should be reading using Ohms law for the series circuit.

I'm using the same resistor that came with the new coil, are there other coil variations excluding the early ones without the ballast resistor?

 

 

1 hour ago, J.R. said:

You should check where that red wire goes to, it should be the starter solenoid and it should have 12v  (probably a bit less) on it only when the engine is cranking.

The red wire goes to where you stated, it was the one that I had to replace as it was burned to a crisp before acquiring the car.

[J.R.]

11 hours ago, Rusty105L said:

Alright, so by the sound of it there's some significant voltage drop on my system? Do you know what to do to address this? Could it be the capacitor that's affecting this?

We dont know what voltage your coil and ballsat set up should be running at, are you sure they are matching complimentary components intended to be used as a pair or were they bought seperately?

 

If the former then measure the resistances and calculate what the volt drop should be, better still hardwire them to the battery with decent section conductor wires (not using the points or condensor) and measure the voltage, if what you are seeing on the car is lower then you have a high resistance connection or wire, possibly the points.

[Rusty105L]

On 10/05/2022 at 09:55, J.R. said:

We dont know what voltage your coil and ballsat set up should be running at, are you sure they are matching complimentary components intended to be used as a pair or were they bought seperately?

Yes, I assume the coil and ballast are compatible as the ballast was already fitted on the coil when I bought it.

This is the coil that I fitted, and the resistances match up to the old coil.
https://www.skopart24.com/en-gb/shop/Zündspule-ab-10-79-p234773436

I measured 1.5 ohms on the ballast resistor, 2 ohms between positive and negative LT on the new coil.

 

On 10/05/2022 at 09:55, J.R. said:

If the former then measure the resistances and calculate what the volt drop should be, better still hardwire them to the battery with decent section conductor wires (not using the points or condensor) and measure the voltage, if what you are seeing on the car is lower then you have a high resistance connection or wire, possibly the points.

 

Just to confirm, you want me to bypass the distributor and connect the negative terminal on the coil to the negative side of the battery?

Also, could the condenser be what's causing this? The original condenser terminal at the points had a melted on plastic piece which broke when I tried to separate them. The new one was not supplied with one. Just wanted to confirm if this is an issue or not since it's been on my mind lately...

[J.R.]

The moving contact point uses that insulator to isolate the spring and moving contact point from earth (except when the points are closed,  looking at your photograph it looks like you have shorted  the coil CB terminal to ground which is why you are not getting any spark.

 

To confirm rotate engine till points are open, with ignition on you should measure 12v across the contacts, without the insulator you will have zero volts.

[KenONeill]

I'd agree; your post reads like you're missing the spring insulator, which should be part of every new set of CB points.

[Rusty105L]

Thanks guys! I'll go ahead and order a new one and keep you posted if it works or not. 😄👍