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  • All you need to know about "Spark plug selection tips."

    Spark plug selection tips. Guide

    The spark is quite literally the life of the engine. A good strong spark makes the difference between thorough combustion and a misfire. Spark plug technology has come a long way over the last few years. First we will look back at the "good old days".

    The components of a spark plug are primarily the tip, the insulation and the electrode. The spark needs to jump the air gap from the tip to the electrode. The bigger this gap the larger the spark will be and the better combustion will be. However too large a gap and you will have trouble getting enough current to jump the gap. Setting the gap size was very critical but with the advent of modern production methods most come correctly set up from the factory.

    After time the tip and electrode will become glazed and this can inhibit conductivity. To combat this problem a clean up with a stiff wire brush will help keep things in tip top condition. Check the ceramic electrode insulator for cracking or tracking. Tracking will be manifest with a black sooty mark. If you spot either they need replacing.

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    The colour of the tip will tell you a lot about your engine. If it is oily and black this would suggest that the engine is running too rich. If it is a light grey soot which covers it you are running too lean. The ideal colour is light non oily mid grey powder coating which is not too thick.

    Modern plugs are made from Iridium and platinum and this allows a much thinner electrode and tip which means the spark is thinner but can be longer and is more exposed to the intake charge. These plugs also require little to no maintenance and will last for 40,000 miles or so.

    There are also a number of multi electrode plugs around and split electrodes. The multi plugs seem to be a good idea but in reality the spark can only travel over 1 at a time (path of least resistance) so the only benefit is a longer life as you have 4 times the surface area. Split electrodes on the other hand mean that more of the spark is exposed. The little nick in the tip allows the spark to ignite the fuel/air mix at the very top center rather than at an edge.

    In the real world you will not notice much of an improvement or difference between a good copper core plug and a fancy multi tip one. If your car specified platinum or iridium you should only use these. Plugs are temperature rated, get this wrong and you risk premature ignition which is really bad for your engine.

    Some engines have separate coil packs for each plug other use just 1 coil. Increasing the coil output will usually mean a much stronger and more reliable spark allowing you to increase the plug gap.

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    5 Responses to “Spark plug selection tips.”

    1. dave bearwood brown says:

      my 124 k astra 1.6 2 valve is missing at low revs in 2nd gear any ideas??? I pulled the plugs wear appears to be even tan gray color Ive been running a a turbo diesel astra 1.8 for the last few years i said i never wanted a petro car again now i remeber why l

    2. admin says:

      Dave – Check the sensors – it is likely your afm/crank/air temp sensors are faulty. Replace the HT leads and check the plugs for tracking. The guys at the http://www.torquecars.com/forums/ will certainly be able to help you.

    3. Renaud says:

      I, my spark plug are looks like there white, not gray. Any idea why?

    4. admin says:

      Hi Renaud, this is actually a very very light grey. Your car is certainly running lean. Check you sensors as above and get some fuel injection cleaner like Redex. (Or ask the guys over at TorqueCars forums.)

    5. Annie says:

      What are the gaps on spark plugs for a Vauxhall Astra Estate 1.6 1997