Hello all,
Generally, how long do HT leads last before they start to go? I ask because my Polo (although running well) seems to have a very slight misfire at idle, which you barely notice, and the exhaust fumes have a slightly strong smell. Not sure if the smell is all that serious or whether its just me. I don't think its running rich , so to speak, as the tailpipe is as clean as a whistle.
A while ago, when I had trouble with the distributor, it was suggest to me (by Peter D I do believe) that the HT leads on these Polo?s are prone to developing high resistances and should be measured. So I have done just that. After a 25 minute drive, I pulled one and out measured the resistance. It should have been 5 Ohms, but this lead was 5.6. Is this bad, as its not that far off really?
Looking at the leads a bit closer, they are showing signs of 'corrosion'. At the distributor end, the outside of the tubular connection is a bit rough and pitted, although the inner edges seem fine. My dad (a sparky by trade) thought they showed signs of arcing.
Am I wasting my money getting new ones? The economy and performance are relatively good (45-50 Mpg, slightly lower than usual but I have been carrying 4 people regularly)
Any thoughts and ideas greatly appreciated
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Missing at tickover --- check your plug gaps are not too small. Take each plug out and look at its colour and you may be able to see the offending (missing) plug by its different colour.
Lead flashover, due to poor quality insulation, usually occurs with hard driving (initial accelleration) as the spark voltage has to be higher.
The plug leads usually have a resistance of one or two 1000 ohms to reduce radio interference and plug erosion. The short one from coil to distributer does not matter if it is just a wire one with a resistance of a few ohms.
Coil voltage is in the thousands and a bit of corrosion is not going to stop it but it is nice to clean it off to stop it going further.
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A very remote possibility, but are your plug leads of the correct gender?
I know that sounds like an odd question - but there are a number of different types of connection between the distributor cap or coil pack and the plug lead. Some incorrect combinations can appear to go together OK, being held in place by the rubber boot, but may not form a good electrical connection.
The older type typically had a hollow cylinder in the distributor cap, and an open, split, metal tube on the end of the plug lead.
The newer type has a small threaded pin in the base of the distibutor cap/coil pack connector, and a small hollow metal cylinder with a small spring clip near the end in the end of the plug lead.
It isn't completely unknown for these to be mixed up by the manufacturer, with one type of fitting on the coil, and the other on the distributor.
number_cruncher
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Thanks for those replies.
The plugs were changed at the last service for Bosch (W7DTC) which means they have the triple electrodes making it very difficult (impossible?) to check or even adjust them. These plugs have less that 3000 miles on them, and with them being OEM ones, I think these should be ok.
The Ohm readings are stamped on the metal sheath as 5 Ohms, so I compared the readings to these. However, I have just gone and bought a set today and they are identical (make) to those currently fitted which are the original 12 year old VAG ones. Strangely, they have higher resistances than those I am about to remove! However, their connections are in considerably better condition than the old ones.
The thought of crossed gendered plugs had never entered my mind number cruncher! The ones currently fitted are the later type you describe with the " small hollow metal cylinder with a small spring clip near the end in the end of the plug lead". These are very tight fit, heeding a firm push and pull to install and remove them. Therefore I assume that they are the correct ones.
Thanks again for those ideas
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Hi,
With this type of plug lead end, if all is well, you should feel the spring clip, clicking over the threads on the pin in the base of the connector in the cap or coil pack as you push the lead end home.
Does your car have a distributor and rotor, or is it one with a coil pack?
Usually if plug leads have burnt out, you get one or two with very high resistance - less than 20K Ohm is usually OK.
What the resistance check doesn't tell you is if the high voltage is leaking out elsewhere, and shorting to earth. Sometimes this can be seen by opening the bonnet at night, and looking for the sparks!
Having said all that, I hope that your car is running better.
number_cruncher
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That model of Polo has 5K ohm caps i.e. 5000 ohms and the leads are copper not carbon. The metal caps can become contaminated and arch across inside so the inside of the cap requires to be cleaned
Has the new leads fixed your problem.
Regards Peter
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Hello again,
Thanks for your further responses, much appreciated.
My car has a distributor, supplied by a single coil. I really wanted to test all leads but could only gain access to one of them. This is because the air cleaner assembly covers all of the remaining three cylinders, and to get at them, it has to be removed. This is a half hour job (well, for the inexperienced like me it is ;-)) By the time I could have them out, they would have cooled off, which would effect the resistances. So, one of the leads may have been a way off the 5K (yeah, forgot to put that [k] in the last couple of times) when warm, but without a quick spell in the oven, I would never know.
The connection on the old leads must have been ok, cos as you say, I could feel the spring clip clicking over the threads on the pin in the base of the connector in the cap as I pushed the lead end home.
The metal caps were crusty/furry on the inside compared to the new ones, and I think they were beyond cleaning, as were the distributor connections. The new Beru leads cost £32.31, and although not the cheapest set on the market, I thought it wasn't a lot for added peace of mind. Also bearing in mind the condition of the old ones, replacement wasn't all that far away, so at least I have had them changed prior to them letting me down when I least want them too, even though they were giving seemingly satisfactory service. Actually, I don't think those old ones liked the damp much either.
So has it fixed the problem? Well seeming, it has, or at least made a difference. All be it not a big one, the car seems to start a bit cleaner and the idle has smoothed out a bit too. The exhaust 'smell' is still present, but not as strong. But it was hard to tell as it was quite windy in the north east today. Really, there is bound to be a smell, so I can't expect a big change here.
Many thanks.
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