[urq] Spark Arches Around Distributor Causing Missfire?

[Ado Sigal]

Usual suspects are: Carbon dust and moisture inside the d/cap, rotor 
position, rubber lead covers and cracks around lead plugs on the cap 
top, and spark plug caps. (leads with Hall ign should have metal core, 
not carbon or fibre)

- Make sure the rotor is exactly lined up with t/mark.

- Its always best to change the cap and the rotor. (get d/cap with 
copper contacts, not alu), but for testing purposes, take the cap off, 
and scrape the oxidation crust from the metal posts. Clean up the carbon 
dust thoroughly from the cap and rotor and wash it off with plenty of 
demoiserising spray, like WD40  (can also spray it inside the distr.). 
Smoothen the carbon contact on distr. with 400 or + s/paper and make 
sure there is sufficient carbon left, and that the spring is strong. On 
final assembly, and to prevent the moisture entering, thoroughly dry the 
cap, the plastic cover plate and distr. contact edge, and apply a light 
coat of non drying sealing compound (Hylomar or similar). Its also good 
to cover the plastic hall plug slot edges where it meets the distr.

- Cover all rubber lead cups (or resistors) inside and outside with very 
light coat of silicone grease (do not touch any painted area with it)

- Since you have 8 mm silicone leads you are probably not using the OM 
caps or resistors, but if you are using them, then metal radio 
interference covers could be shortening through cracks in the rubber cap 
sleeves. You can safely take them of and inspect underneath. (I usually 
take them off from new)

Do one thing at the time and take it for test drive, so you find what 
was the problem.
I've had misfire recently which could not be sorted after swapping all 
the components, until it was checked with engine analyser, where it was 
discovered that rough injector spray was the culprit, and not the HT 
components. After cleaning them all was perfect, so if you have a chance 
to plug it on the analyser do so. It saves enormous time when one can 
analyse the shape of the spark.

Cheers,

Ado




Maurits Jonkergouw wrote:

>Distribitor cap is now 4 years old and does not show visuable cracks. The HT lead in question (also 4 years old) is of the Luminition HV-3 (8 mm) silicon type and 'looks' ok. What are the usual causes for leaking spark arches?
>
>Thanks.
>
>Regards,
>Maurits
>
>1986 quattro GV
>1982 Coupe GL DD
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