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MG Midget and Sprite Technical - Serious ignition fault

The other day a bad misfire started. Much worse on light throttle, with embarrassing backfiring. Even worse last night. I took out the distributor and repaired the earth lead inside (fabric insulation tatty), but could not find anything else wrong. Misfire just as bad this morning. I now find that the positive 12v wire to the coil has overheated and melted the insulation in the loom. I can repair that of course, but why has this happened? The coil is Lucas DLB105 and the low tension resistance is 3.4 ohms, which is correct. Distributor is Lucas 59D4 with pertronix pack. I haven't tested the latter yet and I'm not sure how to. I can revert to points and see if that improves things, but have to repair wiring first.

I just realised that the white wire to the coil is not fused at all, hence there was no fuse to blow. Why was it designed like this?

BTW the car is negative earth, and I have been running with this setup for over 10 years. Something rather odd has happened, but what?

Les
L B Rose

Les,
I can only give my usual stock comments - the thin wires of the igniter heads can be trapped or scuffed, inside the dissy particularly, so are worth a thorough check with a magnifying glass for damage and check there's no strain with plate movement.

Same for the earth wire it needs to be flexible.

Of course any damage inside the insulation won't show up on a visual inspection.

Swapping back to points would eliminate the Pertronix and it's direct wiring so would be a good test for the rest of the wiring and connections.

Depending on how your rev counter is driven you might have noticed it flicker/twitch.
Nigel Atkins

Thanks Nigel

I've had repeated problems with the wires to the Pertronix module breaking off, but when that happens there is no spark at all.

I was just checking the wiring diagram and noticed that the coil case is earthed. I knew this of course and assumed it was via the bracket. But with the test meter I find the case is not conductive - seems to be coated. So what completes the HT circuit? The bracket has gone horribly rusty anyway so was hardly a good connection.

The tacho is mechanical so won't tell me anything about this.

I've now made a new piece of wire and bought a big roll of PVC tape! I think the new wire will go to the other side of the fuse.

Les
L B Rose

Les,

The coil does not need to be earthed to work - the circuit is completed between the ignition switch and the earth side of the points. Coils work normally on fibreglass bodied cars!

We had a Pertonix/Aldon Ignitor unit in a 45D distributor, and after ~10 years it began to misfire occasionally. Traced it to one of the thin wires to the module with a broken wire inside the insulation.

Went back to points, while deciding what to do and decided to fit a 'Nodiz' 3D programmable unit - it is excellent, just need to get an RR session organised to set it up properly.

Richard
Richard Wale

If the positive to the coil has overheated and melted, then there must be a short on the wiring DOWNSTREAM of the melted bit. i.e. between the melted bit and the coil, or if it has melted near to the coil then either an internal short of the coil primary wiring, or a short between coil and distributor.

The other possibility is that you left the ignition switched on - maybe overnight? - with the engine not running and the points happen to be in the closed position? (Or the equivalent to that with the Petronix gismo)


My guess is that the misfire is as a consequence of the overheated/ melted ignition wire, rather than the cause of it. So in repairing the insulaion inside the dizzy, you may have already sorted out the reason for the melted wiring. Replace the melted wire and see ho that works out.
GuyW

Despite the wiring diagram showing an earth for the coil, I was surprised to be told that it didn't need an earth, when the subject cropped up some time ago.

I wired up a spare coil, on the bench, just to test the theory. I can confirm that it doesn't need its own earth.
Dave O'Neill 2

Les,
without knowing the technical side of it I wondered if you might have already solved the problem as Guy has put but thought the route by of testing with points might give reassurance (unless the points are faulty or play up as points sometimes can) as melting wires might take a while to show up.

A break on the igniter wires will stop the unit but a partial break, scuffing or nick in the insulation can present more as a misfire or intermittent problem.
Nigel Atkins

Thanks chaps

The wiring is repaired now so I'll reinstall the coil and see what happens tomorrow.

No I didn't leave the ignition on!

Les
L B Rose

Another option is a double ground... The pos is broken insulation and making contact with the metal of the car somewhere... grommet hole screw put thru the wire

Was the coil ungodly hot also
1 Paper

I've recently seen a similar miss-firing problem on a friends old Ford. It turns out that most of the oil had leaked out of the HT coil, thus causing it to intermittantly short out (internally).....

J Smith

The coil secondary (HT) is connected to the primary (CB terminal) at one end so returns via the points i.e. no other "earth" is required.
Bill Bretherton

Shake the coil. You should hear liquid inside. If you can't it's either full or empty. If it is old it will be empty.

Had this on my Frogeye but mine has a 1275 engine though still retained the dynamo with mech rev counter. I had problems which got worse and worse over a year or so but in the end was almost un-driveable. The coil case became too hot to touch

Rob
MG Moneypit

All fixed now. The very floppy positive cable from the Pertronix was damaged and shorting against the dissy case. An absolute bugger to repair - very fine wire which resisted soldering and had to be repeatedly cleaned. At last the engine fired but it still ran rough. Turned out to be a faulty plug - and I replaced these only 2000 miles ago. I think this was the primary cause. I had the dissy out a few times to try to trace the misfire and probably stressed the cable in the process. Very difficult to identify the duff plug as the misfire was very intermittent and only possible to home in on it when it became constant. Oh what fun.

Les
L B Rose

Congrats Lee

Yepp, China dosnt use the best wiring for the pretronix chips for sure

I always had issues with the insulation breaking down on the wires at the chip its self because of the hinging effect from the sissy plate moving back and forth

I'd get a Simon BBC kit, same as the pretronix but better made (hall effect)

Or pull the chip now while it's still good and replace with points and condenser and keep the chip in the boot for just in case along side a busy highway at night and need a fast and easy emergency ignition replacement kit


They used to be good years ago but about 10 years ago they fell in love with cheap China made crap

P
1 Paper

Les, well done.

Finding the fault on those delicate wires can be a right b*gger and then having an intermittent second hidden compounding fault is the icing on the cake well done on finding both.

Always worth checking the basics too like plugs, rotor arm, cap, and HT leads and replacing all once they are passed their best even if they're still working as it can restore that extra little bit of performance that you'd forgotten about as it had slipped away so gradually.

Nigel Atkins

Nigel, while I agree with you about changing ignition bits that are past their best, personally I wont change plugs until they need changing. As Les said he only changed them recently and no doubt there was nothing wrong with the old ones. I have never held with this idea these days of changing plugs every year even on moderns which tend to have smaller plugs and fire twice per cycle so have a harder life. It also seems common these days to have duff new ones which only seemed to happen very rarely years ago.

Trev
T Mason

Hi Trev,
it was a general comment and about checking items, I can't remember seeing when the plugs or any other of the items were last changed - but I don't remember much.

Sometimes/often when we find the cause of a fault we so relieved we leave it at that rather than whilst we're there looking further potential future issues that might be preventable having seen them now rather than later, or bring forward service items. Yes literally looking for problems but I've found more than once that noticing something and thinking that can wait or when I get arountuit often gets forgotten or causes problems before I deal with it.

I wasn't suggesting changing anything that doesn't need to be changed but the point of change is better before the item affects performance noticeably if you want good performance. To an extent the efficient way to replace may be when they actually cease to reliably work but that depends on how well and how much performance you want out of your car. As performance drop off can be gradual it can be difficult to notice its decline or we get used to the decline and don’t notice. The very few times I get to drive another Spridget I notice a lot more about my midget the next time I drive it.

I don't change plugs every year but usually do every two years because I don't have the equipment or knowledge to know when the plugs have passed their best. Plugs aren't expensive so I'm happy to pay the price to keep up performance. I've only ever had one duff plug and that was a NOS Champion.

I've been caught out previously by rotor arm, dissy cap and HT leads so check them out at services and when I've not Sod's Law has applied.

HT leads are often overlooked they can look good but how do you tell when they're passed their best and they can be of differing quality from new, I've previously proven to a sceptical well known and respected tuner that some HT leads can be better than others and improve performance.

I’ve had enough car problems to last me two life times and don’t enjoy fault diagnosis or rectification so anything that reasonably prevents faults and keeps me driving at best performance reasonably available I’m all for, I only enjoy driving my Midget nothing else on it other than reasonably improving the performance to an acceptable and enjoyable level.

I admit I’m quite happy to spend a bit more to prevent hassle (well as much as is possible, never enough money but always far too much hassle). :)
Nigel Atkins

Sorry Trev,
I now see (I forgot before) that Les put he changed the plugs 2,000 miles ago and I'll take it that Les does more than 1,000 miles a year(?) though that could be many years of use on some Sprites and classics.

I think I picked on two years for plugs as the double copper Champion used to be a two year warranty, that might be many years too soon or months after they pass their best, I can't remember ever researching it.

The more recent (last 10 years) two modern cars we've had I can't remember seeing a time for plug replacement or perhaps it was/is 72,000 miles as that number just jumped into my head.
Nigel Atkins

ETA: just remembered one car was a diesel! so I'll have to check when the current car states plug change.

Now you'll see why I don't rely on my memory and have set points before I forget. :)
Nigel Atkins

I think most moderns state change plugs at every service which for most used to be annually but seem to be a bit longer now (18k in my case) but I still dont think that is necessary. Take them out clean and gap them and replace. They should last years then.

Having said that my son will tell you I expect everything to last years and get annoyed when things dont. We had a debate the other day when he claimed double glazing needed replacing after 20 years. I told him they should last a 100 years which he laughed at. I then pointed out my arguement was based on fact as manufacturers claim they are an improvement yet there are plenty of wooden victorian windows that are still serviceable if looked after. Tell the salesman that and they have no answer.

Trev
T Mason

My XKR is on its original plugs,18 years and 45000 miles on. Change is at 100000 miles.
f pollock

IIRC Ford in the US had a recommended plug change of 100k miles on one engine but by the time that arrived the plugs had grown into the head and frequently broke when removal was attempted requiring potentially expensive work to remove the remains.

I think this was the problem http://www.fordproblems.com/trends/spark-plug-stuck/

Link may have to be copied and pasted as http, the BBS has converted it to https and may not connect as it says insecure.
David Billington

Trev
In fairness, Victorian windows aren't double glazed. We've had to have 20 year old PVC double glazing replaced because the double glazed units had "blown" , not because of the plastic. And double glazed units provide much better heat and sound insulation. I do still prefer the aesthetic appeal of wooden frames though.
Bill Bretherton

Trev
In fairness, Victorian windows aren't double glazed. We've had to have 20 year old PVC double glazing replaced because the double glazed units had "blown" , not because of the plastic.
Bill Bretherton

From a certain well advertised window company site:
"Lifetime guarantee against fog and condensation between the panes of the sealed units"

Often wonder what "Lifetime guarantee" means. Whose lifetime? Or do they mean the lifetime of the product, which would seem to have something of snake-talk about it!
GuyW

David put what I was thinking about 100,000 mile change of the plugs - would they come out and in one piece. I think I'd take them out and give them a glance every 25-30,000 miles or 3 years or so.

Modern cars have computers to work round difference with ignition our cars are not so well equipped so need more frequent checking and possibly adjustment, especially with an old dissy and points. ;)

A couple of companies around here replace misty d/g units leaving the frames.

Nigel Atkins

Nigel
On the 6cyl Fords here the plug change is at 120000 but usually by then the plug gaps have increased that far that coils start packing it in from overload--we tend to change them at 60000 instead
Expensive plugs though-around $120 a set
On the 3 valve v8's with the plugs breaking off, half way through production they changed the design of the sparkplug and the threaded section of the cylinder head, The new plugs have a blank unthreaded section now where the old ones had the thread right up- the old plugs will fit both heads but the new ones will only fit the latter--Trouble is some people fit the earlier plugs in the later heads by mistake and then there's a giant carbon build up in the void in the head and plugs get grown in very quickly
The plugs are down in a hole probably 6"down
lovely job getting them out even with Ford's special easyout kit
willy
William Revit

What am I missing? I was reading about plugs then there was a flash of light in the room and we were talking about window glazing

Is South African apartheid leader Nelson Mandela still alive ... haha

I tend to change plugs every year Inn the spring when I do a good once over on everything to get it ready for the new driving season of spring summer and fall ... at around $1 each why not....

now my work truck.... NOT, THAT'S an all day hellatious adventure
1 Paper

David B

I had a similar experience as you, when posting a link recently. The BBS changed a 'http' URL to 'https'. I edited the post to advise copying and pasting the link, and the 's' disappeared!

Bizarre.
Dave O'Neill 2

Willy,
I had a 25 year old Ford Capri (genuine mileage of less than 100k) with filled-for-life gearbox and/or rear axle (forget which or both) but I do remember one of the oils coming out very watery like and funny colour, obviously they didn't want or expect a life to last 25 years.

The person that bought it from me restored it and uses it as a daily and AFAIK it lives outside and I see it at shows, last year at the NEC again.
Nigel Atkins

Spark plugs notes, info from unestablished sources off Google -

. copper plugs have the shortest life, while plugs made of more advanced and durable materials can provide up to four times the life of a copper spark plug

. the wear that occurs during the last 20% of a spark plug’s life will be more significant

. worn plugs can cause stress on HT leads and coil

. every time they fire, the spark removes some of the metal on the plugs, increasing the voltage necessary to fire the next time

. even if you don't put many miles on your vehicle changing plugs is something that should be done at least every few years

. wire brush cleaning can leave bits of metal

. the business end of the center electrode is actually a 2.5mm-diameter nickel alloy, that’s the largest diameter electrode of all the spark plug types, the smaller the diameter the less voltage required to initiate the spark.

So how long do they typically last? Well, standard copper plugs are said to last anywhere from 10,000 to 20,000 miles (16,093 to 32,187 kilometres).

Looks like checking the gap and (non wire brush) cleaning if required at service intervals seems a reasonable idea - and changing every few years(?).


Nigel Atkins

Dave,

Yes I have noticed that earlier as well. The original link was copied and pasted as a http link but got converted to a https link by the BBS so didn't work, but when edited it showed as a http link and when re-submitted it went through as a http link and worked as intended. I would suspect things to do with the webmaster.
David Billington

Thanks for the congratulations folks, but I had not found every fault. The elusive misfire crept back in last night and the car stopped 3 miles from home. No ignition. The RAC took 40 minutes to answer the phone while I sat in the car slowly freezing. Breakdown man confirmed no ignition, but coil was OK. Towed home.

This morning I found that one of the 4 magnets had fallen out of the Pertronix trigger ring. Fortunately it was not lost as it stuck to the dissy shaft. Another 2 magnets were loose and likely to fall out. The retaining ring had dropped somehow. I have glued them in now.

But still no ignition. The device was not switching at all. So I am back on the old points which work fine. I won't go for Pertronix again because it was not very robust.

Les
L B Rose

Les,
by what Prop puts you'd be lucky to get 10 minutes out of new Pertronix let alone 10 years.

Many seem to find Powerspark igniter heads good and I had no problems with the Aldon when I had it fitted but that still leaves the bottom of the dissy. When I swapped to a fully electronic dissy from existing dissy with Aldon igniter head the different was noticeable from starting up and tickover through the full rev range, I'd recommend a full change to 123 or perhaps CSI.

Don't forget to check the points gap again after a few miles and at 1-500 or so miles and at services (and clean and lubricate points and lubricate dissy as required). Yes I do have a bias against those nasty CB points but they do need checking regardless of my views on them.

Good luck.
Nigel Atkins

Les

Drive it for 30 minutes and then grip your coil and see how hot it is

If it's cooking hot there is probably the ignition wire is grounding out due to a scratched insulation making contact with metal car the points are more robust then electronic ignition

The draw back, the tack becomes your fuse link that gets burnt out...if that's the case

Just because you have the engine started and running dosnt mean the problem thsts causing the issue is actually solved
1 Paper

Received the Powerspark kit on Friday. Difficult. Won't fit the 59D4 unless you cut off the little post on the existing base plate, and they don't mention this in the instructions. They say to use the existing screws, but the base plate of the switch block is much thicker so you can't. Eventually found suitable screws in my boxes of 'things that can't be thrown away'. Once installed the timing is however way out. The unit doesn't stay on and then go off as dissy is turned, it just flashes on momentarily. If this is the timing point, it's over 45 dissy degrees from where it was before. Not at all right, and awaiting reply to my email to supplier. Points back in and engine running fine.

Les
L B Rose

Les,
they obviously need to update the instructions with the unit as it's clearly stated on their website installation guide that you may have to remove the post, with a photo too (see below).

https://blog.simonbbc.com/faq-helper-page/quick-look-at-the-powerspark-ignition-kit-k4-lucas-43d4-45d4-59d4-4-cylinder/


I'm not saying this is the case but it reminds me of the John Twist video of the Pertronix head that is the wrong type for the dissy and is 45 degrees out sparking to the cap posts.



Nigel Atkins

Les - If it's of any help here is a picture of a 59D4 with the Powerspark module in my A35. Don't recall having any issues fitting it, but it was about 7 years ago. Never had to touch it, but having encapsulated silicon leads is de rigueur to allow a clean timing signal at the strobe. Copper wires and screws will mess with the signal. Incidentally I once left the ignition on all night, (and it has an electric pump too) with no ill effects whatsoever - but maybe I was lucky.


f pollock

Fergus,
I might be being over cautious, by the look of your photo the red wire inside the dissy looks a little tight.
BTW, is that a screw in the top of the rotor arm?
Nigel Atkins

Thanks for your concern, but it's just an optical illusion as the red wire has 5mm clearance in any direction. The thing on top of the rotor arm is a bright rivet, standard issue probably. I've never bothered to change it.
f pollock

Just my defective eye(s) again then. :)

I wasn't sure about the screw either but wondered if you might have swapped it out for what might have been a notoriously troublesome rivet on the rotor arm.

Nigel Atkins

I have got the Powerspark working now. What a nightmare. Timing it in the traditional way with a bulb between the coil negative and earth does not work, as it puts the timing way too advanced. I put the points back in and re-timed the dissy, then marked its position. Out it came again and in went the Powerspark, with the dissy back in its original position. The engine fired but only just, and ran horribly. I fiddled with the timing and ended up with an extra 5 dissy degrees over the points. Sadly my timing light is broken and I will re-time when a new one arrives. It really should not be this difficult. The instructions are terrible, and the switching point can't be reliably identified. The supplier says this is because of 'intelligent dwell' whatever that is. Too clever by half I reckon.

Les
L B Rose

If you were happy with the advance curve on points, the easiest thing would be to get your timing light and set the distributor to 30 degrees on full advance - that should automatically give you the correct timing back at idle.
f pollock

Les, when I got mine a few years back now, I too tried static timing to no avail but like you got it to start from the original position and then used a timing light to get it spot on. It varies from the points position because it doesnt sit in exactly the same place. The "intelligent dwell" bit is just the unit electronically adjusting dwell instead of the points doing it manually. I think because it can adjust it is supposed to be more accurate over the whole rev range.

Trev
T Mason

Les,
always remember the posters and Archives here, it's where I read the bulb trick doesn't work on the electronic.

Numbers/figures/settings are good for a starting point but if you want the best running then further road runs and adjustment will be required and ideally a single rolling road session - but just turning the dissy and testing would get many as much as they wanted, with or without a timing gun.

Your engine and ignition system aren't standard so will have their own set of numbers/figures,settings that may or may not match other sets.

Might not quite seem so at the moment but you're getting there, good luck.
Nigel Atkins

I wouldn't say I'm happy with the advance curve. It's for a standard 998 Mini and I'm sure it can take more advance at higher revs. I had a rolling road session at Brian Slark's years ago just after the rebuild, and they thought the advance was OK for the engine spec. Anyway, the basic problem that started this thread is solved.

Les
L B Rose

A trick you could try with electronic ignitions is keep an old transistor radio just tuned in between stations. When the ignition fires you can hear the interference.

Or take number 1 plug out and rig it up so you can see (and hear) the spark.

Rob
MG Moneypit

Not only electronic ignition Mike.
I have used the radio interference click for years when setting up initial timing with points. Only I use the car radio.
GuyW

Well this is one of the big misconceptions About timing, setting up timing (statically???) Just puts the engine in the proper place to start the engine safely after a rebuild or replacing a dissy .. it's never meant to be used as the correct setting to drive the car... that's what the timing gun with dynamic timing is for


Prop
1 Paper

Congrats Lee

It's always good when a plan comes togather


.
1 Paper

One good thing (of many) about Lumenition Optronic, is that you can set static timing with a bulb.
Dave O'Neill 2

Static timing DOES work with the hall effect / reed switch systems like Pertronix / Lumenition and Accuspark, but is only suitable for starting an engine and then timing should be set by getting a timing light out and setting correctly. Note that factory timing settings are probably not ideal with modern fuels.
Dominic Clancy

This thread was discussed between 21/02/2018 and 14/03/2018

MG Midget and Sprite Technical index

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