Electrical Gremlins

[Austin-Rover]

Over the past few months I've had the RAC out to my '84 Maestro 1.3 about four times for the car refusing to start. Each time I got a different 'cause' from the RAC technician about what the problem was. They all got the car started again after a few minutes tinkering. On each occasion the car suffered from a poor spark.

Two days ago on my way to work, the car cut out at a junction, and when the RAC arrived, he diagnosed the same thing - poor spark. This time...even after 40 or so minutes tinkering, he admitted defeat and I was towed home. He suggested the amplifier or the distributor cap. These being the only things he couldn't test or replace at the roadside. Having a brand new amplifier in the garage, I changed this the next morning and the car started first time. To be on the safe side, I changed the HT leads, dizzy cap and rotor arm.

Was the amplifier likely to have been at fault, or is it just a fluke and is the car likely to leave me stranded again? I would have thought if the amplifier was faulty I would get no spark at all, rather than a much reduced one?

Also, on replacing the rotor arm, I noticed the edge of the contact was badly blackened and pitted, apart from one small bit at the end which was still clean and golden. I notice after only two days in the car, the new rotor arm is going the same way as the old one. What is going on?

[Stu_CDX]

Over the past few months I've had the RAC out to my '84 Maestro 1.3 about four times for the car refusing to start. Each time I got a different 'cause' from the RAC technician about what the problem was. They all got the car started again after a few minutes tinkering. On each occasion the car suffered from a poor spark.

Two days ago on my way to work, the car cut out at a junction, and when the RAC arrived, he diagnosed the same thing - poor spark. This time...even after 40 or so minutes tinkering, he admitted defeat and I was towed home. He suggested the amplifier or the distributor cap. These being the only things he couldn't test or replace at the roadside. Having a brand new amplifier in the garage, I changed this the next morning and the car started first time. To be on the safe side, I changed the HT leads, dizzy cap and rotor arm.

Was the amplifier likely to have been at fault, or is it just a fluke and is the car likely to leave me stranded again? I would have thought if the amplifier was faulty I would get no spark at all, rather than a much reduced one?

Also, on replacing the rotor arm, I noticed the edge of the contact was badly blackened and pitted, apart from one small bit at the end which was still clean and golden. I notice after only two days in the car, the new rotor arm is going the same way as the old one. What is going on?

Perhaps the distributor is on it's way out?

I've changed a dizzy cap on a Corsa 1.4 and the original rotor arm has been clean as a whistle.

[G Force]

Hi Rich, you do seem to encounter more than your fair share of unusual but dare I say more interesting problems down the line. As for whether the car will or will not let you down again I wouldn’t dare to guess.

I do struggle sometimes to know what is under the bonnet on your Swiss Maestro but I am guessing the ignition system is the same layout as any early Maestro (amplifier on the bulkhead rather than the distributor) but with no vacuum advance on the distributor.

You are right when you say the amplifier when faulty would generally give no spark or a misfire rather than a weak spark. It is theoretically possible for the amp to cause a weak spark but not typical. What can affect the output voltage of the coil though are poor connections to the amplifier or pickup windings as the amp relies on exacting voltage values to trigger the spark timing point and coil charge time. So with that in mind it is possible that disturbing the connections could affect a cure.

More usually a weak spark is caused by faulty HT components such as coil, cap, rotor arm, HT leads, or spark plugs.

There are a few simple checks you can carry out with a multi-meter to the coil and pickup windings to check to see if there are any problems in these areas.

Check the coil voltage at the + terminal (ignition on) this should be close to battery voltage (not more than 1v below). Voltage at coil – terminal not more than 2v below battery volts, if it is remove amplifier plug and recheck, if then ok the amp is faulty.

Check primary resistance of coil between + & - terminals (wires disconnected) should be around 0.9 Ohms

The next values and tests only apply to early Maestros not the later ones with the ignition amplifier bolted to the distributor.

Check distributor pickup winding resistance (the resistance between the two terminals at the distributor). On the early distributor this should be 2.2 Ohms to 4.8 Ohms. When you test this disturb the wires going into the distributor as you measure, because the wires had a tendency to break on our cars fitted with vacuum advance. Not so much an issue with yours maybe as it was the movement of the base-plate that eventually broke the wires.

Check the air gap between the limb of the reluctor and the pick winding nose. This should be 0.008in to 0.014in. If it needed adjusting I used to set at the lower value, there are two screws that hold the pickup winding to the base-plate just like adjusting a set of contact breakers.

Also, on replacing the rotor arm, I noticed the edge of the contact was badly blackened and pitted, apart from one small bit at the end which was still clean and golden. I notice after only two days in the car, the new rotor arm is going the same way as the old one. What is going on?

It is normal to find the outer edge of the rotor arm burned and pitted in service, but I would not have said as quickly as you have described. Check the rotor arm shaft can be twisted about 10mm (ish) in D.O.R and then springs back to indicate the centrifugal advance mechanism is not seized. A good time to drop a couple of drops of oil down the centre of the distributor shaft (just under rotor arm) to keep the centrifugal advance mechanism lubed. I suppose there will be differences in the tolerances of after market replacement parts dimensions over the years, so it might be worth checking to see if there is a large gap between the rotor arm and each segment contact of the cap, maybe with some ingenious, strategic use of blue tack or plastercine to check this? Any abnormal resistance in the plugs or leads etc. could result in the cap and rotor becoming prematurely burned I suppose, but if the car is running ok it might be just something to monitor periodically to see if it becomes too excessive.

[Peter J]

A Very Interesting and comprehensive reply GForce, Thank You :)

I will print off in case I break down with the same problems.

Incidentally; I wondered if the condenser might have anything to do with it. My engine runs well, so disconnected my condenser as an experiment but it seems to make no difference whether the condenser is connected or not. So I don't know whether it is supposed to do anything other than radio interference suppression. There is no mention of the condenser in Haynes.

I have been checking some spare Maestro ignition leads with a resistance meter. I noticed all have a resistance of about 6 ohms except one which has a resistance of around 80 ohms. Is this a reliable way of checking them :confused:

[G Force]

I will print off in case I break down with the same problems.:

Remember Peter J the data on the pickup winding and air gap setting is for the early maestro not the later modular distributor.;)

Incidentally; I wondered if the condenser might have anything to do with it. My engine runs well, so disconnected my condenser as an experiment but it seems to make no difference whether the condenser is connected or not. So I don't know whether it is supposed to do anything other than radio interference suppression. There is no mention of the condenser in Haynes.:

The capacitor is only for radio interference and does not serve any ignition function unlike the condenser in points ignition systems, however if it did become low resistance it could cause ignition problems.:)

I have been checking some spare Maestro ignition leads with a resistance meter. I noticed all have a resistance of about 6 ohms except one which has a resistance of around 80 ohms. Is this a reliable way of checking them :confused:

Most OE HT leads are made from carbon / fibreglass conductor material and have a high resistance of around 2 Kohms to 5 Kohms per foot. Measuring the resistance does not give much in the way of reliable information as to lead condition. What makes most leads unreliable is the breakdown of the insulation material due to age, heat, contamination and vibration, as well as some burning and degridation of the core.

The only sure way to diagnose HT leads properly is with an engine anyliser with an oscillascope. Or you could touch them whilst the engine is running to test their insulation.:eek: Of course I'm not really suggesting anyone tries this:laugh:

Expect a set of OE leads to only be totally reliable and trouble free for upto as little as 18 months. Some cheap new replacement HT leads can be worse than what you take off and throw in the bin. Unless you spend money on good quality leads you won't get them to last for much longer. I know there will be people who say I've had the original leads on my car and it starts and runs fine, but forget the odd occasion that the car let them down once or twice the odd year ago, and the jerkiness one or two mornings, and the cutting out when cold that went away when the weather got better etc. etc. All caused by failing HT leads.:D

[Peter J]

Another Very Useful Post. Thanks for that G Force :)

Capacitor yes - I was confusing it with the condenser that used to be in the distributor next to the points :o

[G Force]

Capacitor yes - I was confusing it with the condenser that used to be in the distributor next to the points :o

Don't worry Peter J :) Strictly speaking they are the same family what ever we call them, Capacitor, Condenser, suppressor. so you wern't wrong.:D

[BikerGran]

Is the 'amplifier' the same thing that's sometimes called an 'ignition module'? Cos I had one of these fail on my old Citroen, and although when it ultimately failed I was left with a dead car, after it was replaced I realised that it had been causing poor running, particularly under load like going up a long hill.