Hard to identify electrical fault - help!

[southerly95]

Our moggy has a prob which we're finding hard to identify. It's a 65 convertible and is negative earth. Symptoms are:-

- starts ok then begins to lose power after 1/4 mile or so
- this is accompanied by some misfiring which gets worse with some
banging in the exhaust
- finally it won't respond to the throttle although running and finally dies

There isn't much that hasn't been replaced on the car including:
petrol pump, plugs, coil, dizzy cap, rotor arm and leads, unleaded head (all cylinders give 150 psi), carb refurb etc. Carb float is correctly set.

After a while it will start ok again - I don't think it's fuel supply as the pump doesn't 'hammer' when it starts again as it does when building pressure like they do from cold. Both earthing points have been double checked. I have hotwired it in case ignition switch was faulty. All thoughts welcome, thanks, John

[MoggyTech]

Nasty..

Not on your list so if not replaced try the condensor, and even if it was replaced try another one, it might be breaking down under load.

Exhaust backfiring suggest excess fuel that is not being burnt, so check carb float level, and or sticking float chamber needle valve.

Set engine to fast idle, and remove the oil filler cap, any blowback suggest blocked crankcase ventilation hose.

I'd put money on the condensor though.

[steve4063]

i would personally say fuel but as u say the pump isn't going nuts

have u got an in-line filter as they are known to cause problems

check the pipe between the pump and carb especially as soon as it konks out to see if fuel is still coming thru

a friend had similar thing and it turned out to be a leaf in the fuel tank blocking fuel pipe

[LouiseM]

I had an identical problem and it turned out to be a faulty coil. I see that yours has been changed - try putting the old one back on (if you've still got it) and see if that works. Your 'new' coil could be faulty.

[rayofleamington]

I had this on the way through Spain, but Steve's already mentioned what I would suggest (fuel filter).
We got 5 miles before missfires started, and over a number of stops I replaced every single thing on the electrical side before checking fuel (the pump was ticking so I left that till last

Removing the pipe from the carb, you should get a gallon in approx 5 minutes if the pump/tank/filter is ok
e.g. put the end of the pipe securely in to a 1 gallon fuel can and switch the pump off before it overflows!
When playing with petrol, ensure a well ventilated area, no smoking at the time etc... etc...

[pyestudiocolour]

Hi. I had a very similar problem with mine, a couple of years ago. It turned out it was the coil which I had only replaced a couple of weeks earlier. Of course I tried all manner of things to get it going, discounting the coil because of its newness, but once I had limped it home, I put on an old coil and it had no more problems. I bought another new coil and it has been fine since. I no longer buy pattern parts from an autojumble! The duff coil was unbranded and black in colour.

Just don't get me on the topic of the "mechanic" from the breakdown company who hadn't a clue and left my car without fixing it

[bmcecosse]

Sounds like fuel starvation to me - as ray suggests - do a flow test on the pump.

[DanRodd]

i had almost exact symptoms on the M6 this year,was a blocked in line fuel filter,so would check for fuel delivery.Could also be the coil,i bought a new one but went back to the old Lucas one!

[southerly95]

Replaced the coil and wallah it ran perfectly, in fact better than ever - until Friday, thought I'd take her to work and 6 miles out it happened again. Thoughts of John Cleese in Fawlty Towers thrashing his red 1100 and calling it a 'vicious b......d'.

Towed it home again Friday night - well done to SWMBO who was being towed in the dark. I've replaced odd bits of wiring on LT side and removed the electronic ignition and put new points, rotor arm and condenser on plus new plug leads.

Engine starts and seems willing but tries to cut out as though switching off then on again. So - hot wired it and it does the same. Bizarre or what. Fuel side - plenty coming through.

Questions.
1) does the rotor arm rotate anti clockwise with the engine running?
2) is there any possible connection with the red ignition light staying on with the above symtoms. It goes out after a mile or so - during the week when the car was ok that is? Is there any way this could be causing the coil to break down?

Yours frustratedly, John

[Nadir]

Anti-clockwise? Yes.

[Packedup]

Try another coil?

I'm sure I've read about new ones not being so great when mounted horizontally (as it is on the Minor) and giving up quite quickly.

I'm currently running a Lucas gold coil (DLB 105 IIRC) mounted horizontally on the Midget, and so far it's behaved itself. They cost about a fiver more than a normal coil so worth a try IMO

[bmcecosse]

Sounds like a bad wire somewhere - and obviously the Ign light staying on is NOT good - (loose fan belt/worn generator brushes ?) but likely unrelated to this. You have hot-wired - so now try a jump wire direct from the coil to the dizzy to eliminate chances of a broken wire there. Next up consider the little 'Low Tension Wire' inside the dizzy - this can sometimes break and make intermittent contact. Easiest thing would be to try another complete dizzy.

[Pyoor_Kate]

..and check that it's the right kind of coil (i.e. a real 12V one, not one intended for a car with a ballast resistor ('cos they're meant to run at 9 volts)). A quick 'n easy thing to do is see if the coil is hot when the car dies....

My 'becca had many bizzare issues after a while of being off the road (last time) these all disappeared after a thoroughly tedious day of removing every single connection, cleaning and coating in vaseline... Not fun, but handy.

[chickenjohn]

BMC SAID "Next up consider the little 'Low Tension Wire' inside the dizzy - this can sometimes break and make intermittent contact. "

You can get these with the right connectors on each side for a fiver or so from the usual parts suppliers, the wire can look OK but be making a bad connection. Change this wire and see of problem goes away.

Other than that some systematic tests are needed, trace the spark back to ensure ignitios system is not the culprit and check fuel flow when the car is in fault condition.

[Kevin]

Dont forget the Rotor arm I know you have repaced it but there have been some dodgy batches about.

[kennatt]

know you have checked fuel FLOW but have you taken the top off the carb to see if there is enough in the bowl could be that the float needle is sticking not letting enough petrol into the bowl.Sounds like fuel starvation to me .

[southerly95]

..and check that it's the right kind of coil (i.e. a real 12V one, not one intended for a car with a ballast resistor ('cos they're meant to run at 9 volts)). A quick 'n easy thing to do is see if the coil is hot when the car dies....

My 'becca had many bizzare issues after a while of being off the road (last time) these all disappeared after a thoroughly tedious day of removing every single connection, cleaning and coating in vaseline... Not fun, but handy.

Thanks - how do I know which is which? The coil had been quite hot (just touchable) for the period that it was working (I'm assuming it's dead/damaged now cos can't find anything else). It only worked a week!

[Pyoor_Kate]

I'm not certain how you check a coil is a 12V not a 9V (unless you can check it's part number from a catalogue). Mog or classic specialists should be able to sort you with a proper coil tho'. A coil for a ballast resistor'd car will work *really well*, but only briefly. I have one kicking around in the back of the mog, 'cos it's the only thing the RAC had when my coil died; got me home, and kicks around for emergencies.

Given you've not found anything else, I'd try switching it for a new coil, but check up on the fuel issues too

[washer-bottle]

Our moggy has a prob which we're finding hard to identify. It's a 65 convertible and is negative earth. Symptoms are:-

- starts ok then begins to lose power after 1/4 mile or so
- this is accompanied by some misfiring which gets worse with some
banging in the exhaust
- finally it won't respond to the throttle although running and finally dies

As stated earlier this sounds like a coil problem, especially if it is too hot to touch after a short drive. Modern cheap coils supposedly don't like being on their sides or mounted upside down unlike the original Lucas ones as the oil inside doesn't fully immerse the windings.

Now the reason for a faulty coil may be because of a faulty rotor arm causing the HT spark to track to earth through the distributor shaft rather than the spark plugs. This is difficult to spot by eye, but there is a simple test below. As previously mentioned in this thread there are a lot of poor quality pattern rotor arms about, which break down electrically especially if you are running with wider spark gaps driven by high energy sports coils and electronic ignition. Also check that the spring clip in your rotor arm is present and that its a tight fit onto the distributor shaft and its not coming loose once the engine revs up.

The faulty rotor arm test is this.

Turn off ignition.
Apply handbrake and put in neutral.
Disconnect the king lead from the distributor cap (the one from the coil that goes to the centre of the cap).
Remove the distributor cap and wedge it to one side where its safely out of the way.
Turn on ignition.
Hold the end of king lead with insulated pliers close to, but not touching, the metal pad in the top of the rotor arm.
Press the start button inside the engine bay and turn the engine over.
You should NOT see a spark between the king lead and the rotor arm.
You may want to get a friend to turn the engine over so you can use both hands and do this in dim light.

If you see a spark your rotor arm is tracking the HT to earth and is faulty.

(For confirmation if you hold the king lead near the engine metalwork eg a cylinder head nut you should see a spark.
If you don't see a spark in this case then your points, coil, condenser, distributor/coil wiring needs checking as previously mentioned in this thread).

Good luck and let us know what fixed the problem.

Al

[southerly95]

Not been on here for awhile but can say that as advised I replaced the coil with the gold Lucas sports version. I bought this from a mini dealer at link below:
http://www.minispares.com/SearchResults ... e&ty=&rt=1

Not had a problem since and it resolved all the symptoms. This was the 3rd unit in 3 months the difficult part was believing that the two previous coils had failed within days. Thanks for the advice.