Overheating coil?

[Philwesty]

Will to live been and gone.
Runs great until warmed up then the stuttering kicks in until it dies. on restart same thing. I widened the plug gap to 35 and that seemed to help. I have replaced everything in the ignition and gone back to my viper coil after trying 3. it doesnt overheat anymore, which is nice/weird.
I have called my expert so we'll see what happens when he breathes on it.

[Hugo]

I just re-read the posts from the beginning, and I notice that the thread has been "hi-jacked" by two other contributors with similar problems. I don't use that word in a critical sense, but you know what I mean. The upshot is that I have completely lost track of who has done what - in your first post you said the coil was getting hot. I suggest that if you find the reason for that, you will have cured your misfire.
Can you give us a blow-by-blow account of the story so far, so we have it all in one place?

[adam]

Sorry to have confused things with my problem but its now fixed. It turns out it was the regulator box.I found this on the 123 web site.

It looks like my engine misfires after a few kilometers driving what can i do.

In some cases a very unstable boardnet voltage can cause misfire.The 123 ignition is protected against high voltage peaks and goes into protection mode for a split second when a spike is detected.Most of the time this error occurs when the cars battery is charged full again and the voltage regulator starts to work.

This problem can be caused by a broken alternator/ dynamo or bad voltage regulator unfortunately this is impossible to measure with just a standard voltage meter because we talk about high voltage spikes of micro seconds.

You could easily test this to drive a while without working alt/dyn.Use a fully charged car battery and make sure no other important systems are driven by the dynamo belt.Hope this helps someone else out.

[Hugo]

Very useful information - thank you.

[cactusman]

Seems to me the 123 is over sensitive. Cars ARE electrically noisy. For those with RB 340 regulators you can also try connecting a 100 nanofarad capacitor rated at 250 volts (good quality film device) across each of the three points within the RB340. Helps to reduce sparking at the points and may improve your radio too. Voltage spikes at the output can be reduced by connecting a fast acting 20 volt 5 or 10 watt zener diode between the B terminal and ground. The parts can be solder in or on the back of the regulator so will be invisible once the regulator is installed. Available from radiospares or farnell among others...Won't entirely remove the spikes but will help.

[Hugo]

This is such an obscure fault (to me at any rate). I would never have figured it out. Your suffering will no doubt help others!

[JagWaugh]

Seems to me the 123 is over sensitive. Cars ARE electrically noisy. For those with RB 340 regulators you can also try connecting a 100 nanofarad capacitor rated at 250 volts (good quality film device) across each of the three points within the RB340. Helps to reduce sparking at the points and may improve your radio too. Voltage spikes at the output can be reduced by connecting a fast acting 20 volt 5 or 10 watt zener diode between the B terminal and ground. The parts can be solder in or on the back of the regulator so will be invisible once the regulator is installed. Available from radiospares or farnell among others...Won't entirely remove the spikes but will help.

Very clever.

What about installing a MOV on the power supply wire of the 123? I'm thinking of a TR3 that I've got a 123/tune in, we've had it on the scope a few times, and the generator/RB seems to be working flawlessly, but when you're out driving it will sometimes begin to stutter and misfire in about a 5 minute cycle.

I think we tried running the ignition from a booster pack at one point, but tbh we've tried so many things to localize this fault that we've got a list, which I haven't got to hand at the moment.

[mgcjag]

Are you useing carbon or suppression type spark plug wires. Do not use solid core spark plug wires you will get EMI (electromagnetic interference) which could cause misfire....you may have suppressor spark plugs...but what about the coil to cap lead....this wont be suppressed

[cactusman]

An MOV or metal oxide varistor will probably not help much. They will clamp the voltage but their performance curvege will show that it may be at 3 or 4 times their rated voltage....so a 20 volt one ( if you could fine one) would clamp at maybe 80 volts...not much help. They are really intended for use on high power supplies where their ability to absorb power in a spike is far better than a zener diode. A 20 volt zener ( technically and avalanche diode at that voltage) will limit the voltage to very little more than 20 volts providing the spike is short and the overall excess power is within the device limit. Presuming that the supply to the 123 just runs the electronics I would fit a 10 ohm resistor in series with the supply and shunt the supply to ground with a 20 volt zener and 10 uF capacitor in parallels after the resistor. If the thing still went into safe mode I would chuck it in the bin as such an arrangement would ensure no supply line noise got to the unit. It is relatively easy to design noise immunity, both supply line and RFI induced, into a device and 123 should have this in spades. If not then...sorry....flawed design in my view.

[Hugo]

This all sounds like built-in unreliability to me! The kindest thing you can say is that it doesn't seem very robust.
Is it just the 123 ignition that suffers from this 'interference' problem? Or does it also apply to other electronic distributors?
I had a similar issue, as I said in an earlier post, with a Powerspark (or was it Accuspark?) distributor living next to the starter motor on a Morris Minor, that generated random sparks when you cranked the starter motor, with pretty scary results.

[malcolm]

Are you useing carbon or suppression type spark plug wires. Do not use solid core spark plug wires you will get EMI (electromagnetic interference) which could cause misfire....you may have suppressor spark plugs...but what about the coil to cap lead....this wont be suppressed

Steve's post seems very relevant - look at the post I placed here re curing my misfire:

viewtopic.php?f=3&t=10878

[Hugo]

I was getting confused between the two; yours is a Powerspark and the other post was about a 123?

[mgcjag]

They are both electronic ignition systems......all electronics can be effected by EMI interferance

[paydase]

I am not knowledgeable in electronics but following the current ignition threads with interest.
I had recently a hot misfire issue (similar to the one reported by Malcolm) here: viewtopic.php?f=3&t=10878
Mine was resolved by just replacing the small spring behind the central carbon rod in the dizzy cap.
Before the problem was cured, and because I was unable to solve the issue for months, I considered however moving to an electronic dizyy such as the Powerspark one, including replacement of the HT leads (I understand from Malcolm's thread that this may be important) and coil.
I am now a bit uncertain on the interest to move to electronic ignition if the whole ole system needs overhauling to get consistency, such as the need to put additional capacitors, varistors, Zener's and alike to protect components or dampen signals.
I would tend to be with Hugo on this one and stick to points as far as it works!

[Hugo]

I am not knowledgeable in electronics but following the current ignition threads with interest.
I had recently a hot misfire issue (similar to the one reported by Malcolm) here: viewtopic.php?f=3&t=10878
Mine was resolved by just replacing the small spring behind the central carbon rod in the dizzy cap........

Was it? I am a bit wary of this solution, since replacing the spring shouldn't really make much difference, unless the carbon bush was stuck way up inside the cap. You don't need, or even want, a good connection at this point. A spark will jump something like half an inch at atmospheric pressure (less under compression), so as long as the carbon bush is anywhere in the vicinity of the rotor arm, the spark will find its way there. Of course the spark will also be looking for an easier route, so if you have too big a gap at that point, it may try to track to ground via some other route. The only alternative route that occurs to me is via one of the other plug leads, so you will get odd sparks at random cylinders. Or random sparks at odd cylinders. If there is no evidence of this happening, I would be a bit sceptical of your 'cure'. It may just be masking a deeper problem.

[paydase]

Upt to now, it works.
Actually there wasn't any more spring, only a mix of carbon and iron oxide and dust that fell down when I removed the rod which was not sliding any more within the cap, and maybe not even touching the rotor arm.
So probably not the best electrical configuration to transfer voltage, even if HT.
Will see if the issue is definitely cured or if something else comes out...
used rod on left, new one on right:

[Hugo]

You might be lucky. Time will tell. That was my point though - that the bush does not have to make contact with the rotor arm. The HT current will jump anything up to half an inch through open air if it has to, but if it had that far to jump it would probably find a different route home.

[malcolm]

I had recently a hot misfire issue (similar to the one I considered however moving to an electronic dizyy such as the Powerspark one, including replacement of the HT leads (I understand from Malcolm's thread that this may be important) and coil.
I am now a bit uncertain on the interest to move to electronic ignition if the whole ole system needs overhauling to get consistency, such as the need to put additional capacitors, varistors, Zener's and alike to protect components or dampen signals.

With powerspark or similar (Hall) systems, you only need to worry about the HT leads being silicon. The rest is all ok.

[malcolm]

I had recently a hot misfire issue (similar to the one I considered however moving to an electronic dizyy such as the Powerspark one, including replacement of the HT leads (I understand from Malcolm's thread that this may be important) and coil.
I am now a bit uncertain on the interest to move to electronic ignition if the whole ole system needs overhauling to get consistency, such as the need to put additional capacitors, varistors, Zener's and alike to protect components or dampen signals.

With powerspark or similar (Hall) systems, you only need to worry about the HT leads being silicon. The rest is all ok.

[cactusman]

I have an accuspark and copper leads. Resistor plug caps. Works just fine. Silicone leads have a carbon core so you don't need resistor caps or a plug incorporating a resistor. They will still radiate an em field as will any and all ignition systems, in fact any system that generates a voltage that varies rapidly with time...Copper leads per se are NOT a problem so long as there is a resistance somewhere in the HT circuit. And copper leads are physically more robust than silicone ones...i have had silicone leads on my mgb fail internally.
To me the issue here is that the 123 for what ever reason, be that the specific installation or just poor design, seems over sensitive to either the radiated field from the HT or noise in its supply feed.