Club 80-90 Forums

noticed that my spark plug caps look like a lightning stom when my bus is runnin, there shortin out from caps to engine bloke around the plugs, is this just a case of bad leads & caps or is there somthing more i shud b looking at ?
Its a 1986 1.9 petrol engine so its got the long chrome plug caps, any ideas, fanx.

Tis called tracking and obviously not a good thing. Voltage this high is just trying to find the easiest way to ground and those metal cap shrouds and the cylinder head seem like a better bet than going all the way into that hot wet place (the combustion chamber)
You could remove the metal shrouds ( folder over in several places) this will make 'the jump' less attractive.
Ultimately you may need to look at renewing the plug lead set (depending on the severity of the tracking)

Martin

Nice one fanx for that, new leads on the way fingers crossed that might solve it. ta.

I should add that when I worked at at main VW dealership, removing the metal shields was routine when there was evidence of tracking.....
Also check spark plug gaps as 'too wider' gaps will encourage the high voltage to find an easier route to ground.
fairly narrow gap at 0.7mm

Martin

Thanx martin, ill see how it goes with new leads, what is the cause of "trackin" or is it just one of those things??

good grief get a lead set from GSF or Europarts or Brickwerks as soon as possible...

IT'S DANGEROUS

Thanx, new leads on way, any idea what causes this to happen ?

The insulation around the core or the cap becomes brittle and cracks open, allowing the high voltage current to find an easy route to ground

fanx

Much more common than you might think and not necessarily an indication of part failure.
The main dealers (in the first instance) just remove the metal shrouds.
Of course if you are getting a full on arc (total loss of spark to ground) then absolutely change the leads.

You can just change them anyway but as I say, a tiny firework display in a dark engine bay on a cold evening is not unusual at all.

Martin

Let me explain the miracle of the SI (spark ignition engine) I say miracle because it's amazing the high voltage ever gets to the spark plug! let me explain.
The coil produces very high voltage (10,000 - 25,000 volts) and higher depending on type, this high voltage has to first travel down a king lead which isn't made of copper but carbon inpregnated fibre string which itself has a resistance designed to surpress radio signals (radio interference) This voltage reaches a carbon bush which contacts a brass contact on the rotor arm (another point of resistance for the power to flow) Then it travels down a rotor arm, these also have a built in resistor (depending on type) offering yet more restriction for the high voltage to flow. Then it reaches an air gap in the distributor which the high voltage has to jump (yet more resistance to flow) once across to the individual segment of the cap it is routed to a HT lead (high tension) yes you've guessed it, yet more carbon inpregnated string with yet more resistance built in for radio supression, it then travels to the spark plug cap OH NO! this is a resistor cap WITH..yes, more resistance for radio supression, have we reached the spark plug yet? no, not quite, some plugs also have resistors built in, THANK GOD not the ones used in wasserboxers. Has the high voltage reached the end of it's journey, not quite, as it has just entered one of the most hostile enviroments known to a spark, damp/wet/cold surrounded by very tempting metal surfaces, pretty much the worst possible place to ask high voltage to carry out the trick of jumping an electrode in order to cause a single combustion. That little 0.7mm gap could take anything between 12 and 15,000 volts to jump so it's understandable that occasionally he chickens out and takes an easier journey.

NO WONDER the high voltage tries to escape on the way!

Martin