MatraSport Forum

I have got my 1.6 Murena back on the road after being laid up for 6 months. However it has developed a fault - the engine idles well but cuts out on a run and often won't restart. It doesn't even fire so it seems to be an ignition problem. The distributor may be switching because the rev counter needle occasionally moves as the engine turns over but it doesn't start. I guess this means it is a problem on the high tension side so I will investigate that - but it appears to have the original amplifier - should I also suspect that?  Has anyone converted the ignition to a more modern system - is there a 123 distributor that works (am I right that the distributor its the same as 4 cylinder BMWs from the 1980s?).

Any help/suggestions will be appreciated.

Thanks
Tom

Hello Tom,

You don't say how you get it running again or back home, if it won't restart after it has cut out?  It is simply a case of waiting a while and then it starts again?  However you rectify it, it is important for me to know if I am to try to work out what is happening without being able to test the car.

The distributor can be one of two but usually they are the Bosch 0.237.020.039 - or it might be a Ducellier 525296B.  Neither will be the same as any BMW or any other car!  All distributors are individually tailored to each brand and model, and have the characteristics set for mechanical and vacuum advance and/or retard, as well as in this case the amplifier it is set to work with, so please don't think you can buy one for another car/model and it will work.

However, please, you are not diagnosing the problem, you are guessing.  That is a sure way to spend money without curing the fault.  If it stops and won't restart that is an ideal time to test for the fault.  The worst is when it stop but then restarts as the fault is unlikely to be easily traced.  You say 'should I suspect the amplifier' - why, simply because it is old?  That is not the correct way to diagnose anything.  These amplifiers don't generally fail that much, and again there are other things that you need to check first.  Plus you should realise these amplifiers are now extremely difficult to obtain, so if it has failed you might be in trouble!  But if an amplifier fails why would it be intermittent?  It usually either fails and that is it, or it doesn't.  In your case the fault is intermittent which tends to suggest something else.

But you can do various other tests anyway to check for possible faulty items.  You say the amplifier is the original but what about the coil?  That is something that can break down when it gets hot and won't allow a restart until it gets cool again.  If it is original then it might be as well to change it anyway after all this time, but you can easily test a coil anyway - the resistance across the low tension should be 1.5 ohms and if you take the king lead out of the distributor and hold it a small distance (say 1mm) from the head/block and crank the engine, you should get a series of blue sparks, if it is good.

Also you don't mention the spark plugs you have fitted.  I hope they are not the modern ones with multiple electrodes or special materials like iridium and very large gaps, as these are designed for the modern high current ignition systems usually with a coil over each plug.  Sellers advertise them as superior plugs, but in reality for an older car, they are superior only at earning them extra profit!  For a classic system like the Murena all you need is a good copper plug with single earth electrode and a gap of 0.6 to 0.7mm at most.  A distributor cap, rotor arm and system can't handle much more than 26kV whilst these modern systems are often pushing out 60 to 80 kV.

If you have taken a look at my website and the parts section, you will find various part numbers there for things like the coil and plugs, and distributor caps and rotor arms.  If you need plug leads I can make them up to the correct lengths.

But first you need to diagnose the problem logically.

Roy

Hi Roy
Thanks for the reply. I was resorting to guesswork because the issue is so intermittent. Last time it cut out at about 20mph in third and wouldn't restart but once we had towed it home it started first turn.

However I just checked the low tension side of the coil (1.6 ohms) and found one of the spade connections to it was loose and corroded. So embarrassingly it may be one of those basic things that I should have found without worrying about more complicated faults (or troubling the forum)!

The plugs are NGK BP6E. Other issues that occurred during the process of getting it back on the road that I don't think are contributing to the current problem were - blocking of the idle jets (now ok after some running time) and a broken rotor arm (the piece of metal that 'fixes' it to the shaft became detached).

I will remake all the connections to the coil and do some test drives but take tools and multimeter etc so I can do some tests if the problem persists.

I have had good experience of fitting an aftermarket 123 distributor to an MG Midget - but I guess even if they made one to fit the Murena it would not greatly improve on the standard system in the same way.

Tom

I note that you had to replace the rotor arm.  Some aftermarket rotor arms are of poor quality and can give the symptoms you describe, following on from Roy's advice, if you get a good spark at the king lead but none at the plugs, this could be the problem.  Also, you seem to have jumped to the conclusion that it is the ignition.  Have you checked the fuel supply.  You should have an in-line fuel filter between the pump and the carb, which will provide an instant visual check on the fuel supply.  If you don't have a filter you will be constantly plagued with blocked idle jets, so it's always worth fitting one.

Thanks Pete
The new rotor arm is an Intermotor (at least that's what it said on the ebay advert and the box!).

I fitted one of these inline filters when I put it back on the road - https://www.merlinmotorsport.co.uk/p/sytec-fuel-filter-8mm-in-and-out-with-bracket-ssfc5160c it is described as being ok for low pressure systems but I suppose it may be restricting the flow.

I am sure you are right - if/when it does it again I will check for a fuel problem too.

Tom

I had assumed that the filter was a transparent one.  That ought to be man enough for the job though.

My gues (not scientific) because  it happened several times to me.
The wires on the module have contact problems.
The wires are to loose to make good contact.
When driving, vibrations will let you loose a contact there,
Push the plug a few times of and on and you go again
Narrow the female connectors  a bit to make a better contact.
Because these contacts are old it will happen again (NB the metal is tired)..
To me 3x in the last 7 years.
Better is to measure the problem out logical but if you are on the road that comes second.

Greetz Herman

Could be the ignition. I know that the earth of the black "box" can be corroded and give problems and all connectors are of course old. However this would not really explain why it should work again first time you tried to start it again after being towed home.

My guess would be that it has either to do with the temperature of the engine/wires etc. (coils tend to fail at higher temps) or it was something whole altogether (drowned by too much fuel that evapourated during the tow home?)

We can simply not say what it could have been and there is a LOT that can go wrong on a 35 year old engine. Best is to do some advanced maintenance to wiring etc. check them for fit and corrosion. Measure the resistance in your plugwires cold and running temp. (from the inside of the distributer cap so you get the actual reading of cap plus wire) and things like that that won't cost you a lot of money. If it would stall again you have a good opportunity to investigate further.

Yes I agree, trying to diagnose an intermittent fault is very difficult when it is in fact working, and the best time is when it has failed.  However, you can do some checks and tests even when it is working, and just as you have now found that loose coil connection, some things can be easy to find when you really start to look, some require a bit more experience.

Blocked idle jets can be quite common especially on the 1.6 even after you have cleaned them out.  Sometimes you need to put a new filter on, although once I was actually caught out after fitting a new filter - bits of the filter kept coming through and blocking my idle jet (on a 2.2 as well which is not quite as common as the 1.6) and of course I didn't suspect the filter!  After eliminating everything else, I decided the only thing that had changed recently was the filter so I changed it again, and that cured it!

The engine loom has an earth on the suspension tower and you need to make sure that is good - the zinc can creep under it and degrade the contact.  Also as Herman states, on a 1.6 you need to check the terminals in the wiring plug to the amplifier as one in particular can get pushed back into the plug and not make good contact.

Obviously also check amplifier earth and the engine earth braid.  Earths are often overlooked.

Those NGK plugs are fine.  I've always used BP6ES, but BP6E are virtually the same and either will do.

Roy

Thanks everyone for your help and suggestions - I will work through all the wiring and connectors and embark on some cautious test drives.

Regards

Tom

Quote Roy.
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 bits of the filter kept coming through and blocking my idle jet (on a 2.2 as well which is not quite as common as the 1.6) and of course I didn't suspect the filter!
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Also happened on  my 1.6
(http://www.matramania.be/phpBB3/download/file.php?id=9004)

Those foam-filters are terrible, especially when they age! Isn't there a replacement element for them without the foam?

If I remember well there was one from Fram but that didn't fit ::)
There is a lot of misleading info about parts for our cars.
In between sercvie I turn it a 1/4 round sometimes so the hole for the outside air changes to a fresh part.

I bought a K&N long life air filter for the 2.2 some years ago, and these are much better, but more costly to buy in the first instance.  However, once bought you never need to change it again, just clean and re-oil it occasionally.

Sadly K&N have stopped making this particular one now. :(

Roy