Yet another misfire, someone said could be secondary ignition.
In simple speak what is it and how would it be fixed on a mk3 16v Golf?.
cheers Robby
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Secondary ignition is caused by something staying red hot in the combustion chamber --- usually carbon deposits. This heat then lights/fires the mixture as the piston comes to the top on the compression stroke where it would normally be fired by the spark from the plug. Thus you can/could switch off the ignition and the engine would still run on for a few firings in a lumpy sort of way because the firing is not as well controlled as it is with a spark plug or diesel fuel injection.
To get rid of it you had to do a decoke --- take the cyclinder head off and get rid of the carbon deposit/s on the piston top and the valve ends.
Does not seem to happen much these days with modern engines and oils.
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Thanks ,wouild an after market additive like 40000+ to burn off deposits be o.k to use rather than stripping head ,as you said a modern engine shouldn`t need it and it`s only done 60000.
Cheers Robby
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Hi Robby,
Firstly, I suspect that one of our dear and beloved moderators will soon transfer this thread to \"Technical Matters\".
What an excellent idea. ND
Secondly, I have to pull Buzzbee up by his whiskers. I think what he is reffering to is \"pinking\" or \"detonation\". Your question asks \"what is secondary ignition ?\".
The basic ignition system comprises of two parts, the \"primary\" or low-voltage side and the \"secondary\" or high-voltage side. The primary 12volt supply to the coil(s) is switched on and off by either the points or the electronics (of a modern system) and this creates a \"secondary\" high-voltage discharge from the coil(s) which is what causes the plugs to spark. Most ignition-related misfires are due to insulation faults on the secondary ignition circuit (ie, the coil tower(s), distribor cap rotor if appropriate, HT leads, and plugs caps/covers) or faults with the plugs themselves. A skilled engine diagnostician should be able to pin-point such problems.
Regards, Adam
Whatever is rightly done, however humble, is noble.
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Good answers from both Buzbee and Adam, even if Buzbee misunderstood the question (I did likewise).
This is an example of what I like about this forum. We amateurs try to provide answers and often get it right ... but if we don't there's always an expert looking over our shoulders to correct us.
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If they haven't been replaced for a while, and they only last a few years nowadays anyway, then you could start by just replacing the distributor cap,rotor arm, HT leads and spark plugs. That's worth doing anyway, but if it doesn't fix it then I agree, get it diagnosed by an Adam Tune-up.
I had one recently (not by Adam) to try and pinpoint some annoying little blips, and it was the best value £50 I've ever spent. I got a complete diagnosis of the whole ignition and fuel systems, and the education that came with it while watching the bloke explaining what whas going on was an eye-opener. It was a bit like doing an NVQ in car diagnostics in one hour.
I now know what the ignition amplifier module does, how to test the injectors, how the fuel pressure regulator works, why a dirty coil can destroy the ECU, etc.
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Too true Cliff, Tune up answers in the backroom always get my full attention.
" I write a technical column for the local weekly paper, a collection of which I am considering publishing in book form soon."
...So Adam, when's the launch party?
Stu.
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Re. your misfire. If your 16v has the same single ignition coil as my 8v (Temic 6N0 905 104) check the HT tower for an internal and external hairline crack.
Quick way to check is with the engine off on a pitch black night, dampen the coil tower with water. Start the engine and look for any sparks. You might see part of your plug leads glow with corona (not spark) this is normal. Best of luck.
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Thanks to all ,Get the car back from the dyno center on Monday,with a bit of luck fixed, a new set of leads being given the task of saving the car( and my sanity).Doubtfull as I think that is too easy ,and new set only fitted 12 weeks ago.
Failing that at Least I`ve got a few more avenues to explore thanks to this excellent site.
Watch this space,
Robby
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If your question, as now seems likely, was about misfiring that happens while the engine is supposed to be running normally, like intermittant engine noise or bangs from the exhaust, as oposed to what I described which is what can happen after the ignition has been switched off, then it is likely you have an ignition problem as has been suggested -- I am growing new whiskers.
As to my description fitting that of an engine pinking or detonation, no I was not describing that. Pinking is due to the rate of burn of air-petrol mixture in the cyclinder head exceeding the speed of sound -- the mixture goes bang. To stop pinking, lead was added in petrol (not used now) as it slowed down the burn.
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