Weak Spark - Why?

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Landlover99

Landlover99

Active Member
Posts
283
Location
Extreme North West
Hi all,

The V8 I bought recently was becoming more reluctant to start and this morning I couldn't get it running at all. I pulled off the petrol pipe and spun 'er over and fuel positively gushed out. So I grabbed the HT coil output lead, disconnected it from the centre of the dizzy and coiled it back over itself to leave a gap of about 10mm I guess from ground. Spun 'er over again and the spark's very anaemic looking I have to say; kind of thin and yellow. What's the most likely cause of this? I'm not sure due to the fact that it's got one of those "factory set/leave alone!" dizzys which use some kind of reluctance wheel. I know where I am with cap and points but not this new fangled thing from 1989! Any suggestions?
LL
 
Landlover99 said:
Hi all,

The V8 I bought recently was becoming more reluctant to start and this morning I couldn't get it running at all. I pulled off the petrol pipe and spun 'er over and fuel positively gushed out. So I grabbed the HT coil output lead, disconnected it from the centre of the dizzy and coiled it back over itself to leave a gap of about 10mm I guess from ground. Spun 'er over again and the spark's very anaemic looking I have to say; kind of thin and yellow. What's the most likely cause of this? I'm not sure due to the fact that it's got one of those "factory set/leave alone!" dizzys which use some kind of reluctance wheel. I know where I am with cap and points but not this new fangled thing from 1989! Any suggestions?
LL
Click to expand...
Modulator on the side of the distributor can fail miserably. I had this happen once going to work. Only until an auto electrician found the problem I too was left with scratch bonce.🥴
 
Landlover99 said:
"Modulator? Never heard of that! Bloody modern technology. Okay, thanks, I'll look into it. Any idea what its function is?
Click to expand...
Its called an ignition control module, "The ignition control module is a crucial component of a vehicle's ignition system. It controls the ignition timing and spark generation, ensuring efficient combustion and optimal engine performance. It interacts with other components, such as the ignition coil and distributor, to generate sparks immediately."

So it takes the signal from the sensor and then does the biz to make the coil make a spark...... I spose!

Had one go on a Mini once. Right pain.

So it does the same as the contacts (and condenser) used to do.
 
Stanleysteamer said:
Its called an ignition control module, "The ignition control module is a crucial component of a vehicle's ignition system. It controls the ignition timing and spark generation, ensuring efficient combustion and optimal engine performance. It interacts with other components, such as the ignition coil and distributor, to generate sparks immediately."

So it takes the signal from the sensor and then does the biz to make the coil make a spark...... I spose!

Had one go on a Mini once. Right pain.

So it does the same as the contacts (and condenser) used to do.
Click to expand...
What he said
IMG_20250626_211750_2~2.jpg
 
What? So it's just some fancy name for an ignition amplifier? Takes the weak signal from the reluctor sensor in the dizzy and boosts it up to 12V pulses for the HT coil's input terminals? I was given to understand that the ignition amplifier (if that's what it is and it sure sounds like it) was a separate module next to the coil. But now youz are saying it's built into the actual dizzy body?
 
Landlover99 said:
What? So it's just some fancy name for an ignition amplifier? Takes the weak signal from the reluctor sensor in the dizzy and boosts it up to 12V pulses for the HT coil's input terminals? I was given to understand that the ignition amplifier (if that's what it is and it sure sounds like it) was a separate module next to the coil. But now youz are saying it's built into the actual dizzy body?
Click to expand...
IMG_20250717_164251_1~2.jpg
 
Landlover99 said:
What? So it's just some fancy name for an ignition amplifier? Takes the weak signal from the reluctor sensor in the dizzy and boosts it up to 12V pulses for the HT coil's input terminals? I was given to understand that the ignition amplifier (if that's what it is and it sure sounds like it) was a separate module next to the coil. But now youz are saying it's built into the actual dizzy body?
Click to expand...
Without pics and other indications, we don't know. It could be some aftermarket thing. Many do come with it inbuilt, but not all.

I fitted one not long ago, I bought a trad dizzy and a kit to convert it to elelctronic ignition. It all sat inside the dizzy. (To an aircooled, Beetle based, kit car. )
 
Forget the naysayers here my V8 compadre. Although your ignition amplifier is mounted to the distributor, it still needs a good earth, through its base contact with the distributor. Early amp units had one, (3 wire), and then they changed to two, after assuming the amp had a good earth. Not a great idea...
For a test, I suggest running a small size wire between the distributor body and the battery negative. This will negate any electrical resistance through O rings and general grime between distributor body and a good ground. Those amp units have a reputation for being unreliable, but only when the engine is hot. Hence the Disco V8 factory fitted "remote mounted amp".
Having problems while cold is an odd one. Is your coil being fed 12volts? Can you borrow a coil from a buddy? Can you try your coil on a buddy's vehicle? Please advise.
 
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