spark plug shrouds?

[Gold4.3]

Hello again,
As I am new to the Griff,and do not have a copy of the Heath 'Bible'as yet,is it ok for what I presume are the s/plug 'shrouds'to flap about abit or should they be a tight fit?also after starting,sometimes taking quite a time,the engine will just die when starting out on a trip,although goes great when up and running,
Thanks

[GreenV8S]

The spark plug shrouds should be a tight fit on the plugs and the HT leads should be a tight fit on the shrouds. They should be located by a metal clip in the shround that engages on the metal terminal on the top of the plug. The shroud also has a rubber seal on the inside, if it isn't fitted correctly the rubber seal can hold it roughly in place without the metal contact engaging properly. It's possible for the metal clip inside the shround to be damaged in which case it won't grip the plug properly. The shrouds also tend to fail electrically over time. If in doubt I suggest you take the shrouds off completely and connect the HT leads directly to the plugs. It will run fine like this as a temporary measure, but it will bring the HT leads close to the exhaust and they will suffer heat damage eventually. If this cures the problem then the shrouds are faulty/incorrectly fitted. ACT are the best source for replacement shrouds.

[shadowfax]

Blimey : "Shroud". What a term for summat that, if it aint working efficiently, could see the driver wearing one.

[steve-v8s]

The “ Shrouds” are actually suppressor caps and contain a resistor to slightly change the profile of the spark. To confuse the issue there are also some around without the resistor. Probably would make no difference to engine performance but may trouble the radio (if you use one ! ). They are a GM part and available from Vauxhall dealers. But as said ACT also stock them and tend to be slightly cheaper. I changed all eight because the internal spring contact had fallen apart on one of them causing a misfire.

[GreenV8S]

Word on the street is that the correct ones are non-resistive and serve only to move the HT lead away from the exhaust heat. The factory have supplied resistive ones in the past, but I suspect this is for economic rather than engineering reasons.

[steve-v8s]

Think mine were original fit and were resistive. All the resistor does is slightly change the shape of the wave form as the spark starts. A perfect square wave contains infinite harmonics which is why it causes radio interference. Slightly slowing (and we are talking Pico seconds here) the rise in current will reduce the harmonic current. Once the spark has started the resistor has no effect. As most HT leads are resistive any way it probably makes no odds which you use.

[griffter]

steve-v8s said:

Think mine were original fit and were resistive. All the resistor does is slightly change the shape of the wave form as the spark starts. A perfect square wave contains infinite harmonics which is why it causes radio interference. Slightly slowing (and we are talking Pico seconds here) the rise in current will reduce the harmonic current. Once the spark has started the resistor has no effect. As most HT leads are resistive any way it probably makes no odds which you use.

I changed from resistive to non resistive (from ACT) with no side effects (other than peace of mind).