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