Misfire when warm, recurring problem

[ashleywakeling]

Hi all,

Unfortunately in June I had my moggy stolen. We got it back, but we've had a long list of continual problems since then with pretty much everything. The moron who stole the car managed to trash the clutch and gearbox. I've had them both replaced, and they are now fine. Recently my "aftermarket and therefore CRAP" condenser went, I replaced it with another, which then died within 30 miles. The debate about the standard of new parts however is a debate for another day. I bought a GOOD condenser and it doesn't seem to be giving us issues.

My commute to work is 20 miles round trip and Florence behaves fine. However, I went to Cardiff yesterday (about 45 miles each way). She made it fine, no problems, but on the way back, after about 20 miles in the horrendous weather, she developed an almost regular misfire especially when under load, but fired fine when stationary or not at speed. I dropped my speed on the motorway to 50 to try to counteract the issue but it didn't prove fruitful.

She seems to drive around town and do short distances without much hassle, but when she gets hot, she misbehaves. I have got a carb-rebuild kit, but I don't feel educated enough to try it myself. Is there anything I should be checking before I attempt it?

Thank-you guys.

[minor65]

Sounds like a points issue or possibly damp inside the distributor cap. I would be starting with checking the points or replace them (with lucas ones)

[Nickol]

If that is the case, lift the bonnet after dark and run the engine at various Speeds to see if any arching is occurring. It will be easily seen.

[bmcecosse]

In this weather - it could be carb icing. Is the inlet pipe on the air cleaner turned to point at the exhaust manifold?

[dalebrignall]

if its a really wet day the distributer gets soaked take the cap off wipe it with a rag and spray wd40 on the cap and leads should work fine after that

[bmcecosse]

While that's fine to 'get you going' - the WD40 leaves behind a sticky residue...which attracts filth - and makes the problem worse in future...

[kennatt]

has it had a NEW coil fitted at some time, would be worth finding a known good OLD coil and trying that,been a lot of NEW coil issue.

[bmcecosse]

While it is worth trying another coil just to settle the matter - my view is that coils either work - or they don't. There's nothing inside a coil that is temperature sensitive. And yes - NEW coils are often poorly made, or wrongly specified to work with 9 volt 'ballast' ignition systems. These draw a huge current when used on the normal 14 volt car system - burning the points and ruining the condenser very quickly. Great spark while they last! Coil connections are always something worth checking - I suppose they could start to 'fizzle' with use if there is dirt/corrosion present.

[liammonty]

While it is worth trying another coil just to settle the matter - my view is that coils either work - or they don't. There's nothing inside a coil that is temperature sensitive.

It may be your view, but experience, both mine, and others, shows that it isn't the case. I have experienced two different coils that gave exactly these symptoms.

[simmitc]

Does the misfire occur under all engine sppeds? What I'm getting at is whether it is related to revs or load? Always worth a compression test to rule out those problems. Is the radiator level steady or are you losing any coolant. I agree that copils can go wrong when hot - I had a persistent problem with one doing exatly that and giving your symptoms. I went therough the whole gambit of other solutions before eventually changing the coil, after which all was fine.

[bmcecosse]

There are only 'coils' of wire and a solid core inside an ignition coil - so what can be temperature sensitive about that?

[liammonty]

There are only 'coils' of wire and a solid core inside an ignition coil - so what can be temperature sensitive about that?

This does happen, and that's a fact, that I've experienced several times and eliminated all other causes.

My degrees are both in biology, not physics, but I would imagine that increased temperature would lead to greater resistance within the coil - that, I suspect, would cause a progressive deterioration in the spark. I await the expertise of someone with more knowledge on electronics and/or physics!

[bmcecosse]

It would need to get extremely hot to make a difference - and I can only see that happening if it is a 9 volt coil running on 14 volts - or perhaps if the casing has been damaged and the oil allowed to run out......

[liammonty]

Many of the new coils are not fully filled with oil - that could be the problem.

[dalebrignall]

thats all the wd40 comment was intended to be its saved my bacon a few times . if you have to get a new coil get the red one from accuspark , make sure the connections are good and tight . dont get a lucas one all made in china now and are poor qualiaty .

[bmcecosse]

But - hang on - if China is going to build our Nuclear Power stations - surely they can run off a few coils ???????

[SteveClem]

The Chinese can build anything to whatever quality is required. I think we should be questioning the uk companies who are commissioning these parts at rock bottom prices.

[bmcecosse]

Problem is - I doubt the reactors will be at 'rock bottom' prices.... Oh I see - you mean the crappy coils !

[kennatt]

I know roy has a strong view on coils,and I respect his views,, but Herewith three of my old cars with the same problem all cured by simply changing the coil.
Renaut 12 ,, A35 ,. 1960 mgb Same faults cured without touching anything else in the ignition or fuel system,,,as a result I always carry a spare OLD coil,and transfer position away from the alternator/dynamo and put them on the inner wing away from the heat from the engine

[liammonty]

I know roy has a strong view on coils,and I respect his views,, but Herewith three of my old cars with the same problem all cured by simply changing the coil.
Renaut 12 ,, A35 ,. 1960 mgb Same faults cured without touching anything else in the ignition or fuel system,,,as a result I always carry a spare OLD coil,and transfer position away from the alternator/dynamo and put them on the inner wing away from the heat from the engine

Agreed. It happens, and it's fact. Agreed that unfortunately it's far more common with modern cheaply made replacements. In my experience, it does also happen to be heat-related. Also agreed that fitting a coil designed for a ballast-resistor ignition system to a standard 12 volt system will guarantee a swift failure, but unfortunately it can also happen with coils of the supposedly correct spec. Of the several I've had fail, only one failed totally instantaneously, the others all got worse with heat, then improved after they had cooled. That's why it took me a long time to diagnose the problems. And let's give credit where it's due to the Chinese - the 'Lucas' coils today are made in India