scottbott wrote:the only reason I replaced the HT leads,dizzy cap and rotor arm was because I have never replaced them in the nearly 4 years I have had the van,it was running sweet as a nut, oil changes get done regular and anything else that needs doing gets done,you know what it is like sometimes I go out to tinker around and make work for myself,I'm sure that I am not the only one that does that
That's exactly my point, whilst I'm not suggesting you have done anything wrong (quite the contrary in fact) there is a general misconception that rotor arms/distributor caps and plug leads routinely need changing whereas VW only recommended changing them when there was evidence of wear or fault...for example; a hairline crack in the distributor cap or excessive erosion of the rotor arm.
I'm kind of playing devil's advocate here, because the arcing fault I describe with the tin shields is 'prevented' by changing leads...my point is VW did actually recognise this fault and wouldn't authorise plug lead replacement under warranty until the tin shields were removed and the vehicle re-tested for the reported misfire....in most cases the removal of these suppressor shields would eliminate the customers misfire and VW saved the cost of plug lead replacement.
So to describe what is happening: the high voltage travelling down the ignition lead meets the 5Kohm resistor in the cap and chooses to take the easier route of jumping from the copper wire to the metal shroud and to the cylinder head rather than 'forcing' it's way through the resistor, down the centre electrode of the spark plug to then 'jump' the 0.7mm gap to 'make ground'.
Removing the metal shrouds makes the latter choice the easier route and correct ignition takes place.
Martin
