Urgent ignition problem help

Bart · Post by **Bart** » Mon Sep 15, 2014 5:30 pm

Hi,

I started my car this evening to find it is missing and running badly. It's my every day car, so I need to fix it kind of urgently. Hope it keeps going until I can fix it.

Tried to disconnect each ignition lead in turn, and the engine note drops slightly with each one EXCEPT No 4 which makes the engine note go up slightly!

Is this likely to be caused by a dodgy lead?

If it is, I could do with a make shift replacement one until I can afford new proper ones.

ChrisJC · Post by **ChrisJC** » Mon Sep 15, 2014 8:01 pm

It does sound like No.4. You could swap the lead with No. 6 lead as I think those two are about the same length. Then see if the issue has moved to No. 6.

If you have fuel injection, then you should also consider the injector on No. 4

Chris.

Bart · Post by **Bart** » Mon Sep 15, 2014 8:19 pm

Drama over. Turned out to be the No 4 plug. Managed to hobble to Halfords and change it in the car park before it went dark lol.

What makes a spark plug just give up like that? Was fine this morning. They must only have done about 3K.

Denis247 · Post by **Denis247** » Tue Sep 16, 2014 12:01 pm

Bart wrote:Drama over. Turned out to be the No 4 plug. Managed to hobble to Halfords and change it in the car park before it went dark lol.

What makes a spark plug just give up like that? Was fine this morning. They must only have done about 3K.

I've had brand new ones be doa in the past.

ramon alban · Post by **ramon alban** » Thu Sep 18, 2014 8:07 am

Bart wrote:What makes a spark plug just give up like that? Was fine this morning. They must only have done about 3K.

Hello Bart,

Perhaps half a dozen reasons why a new spark plug will fail prematurely.

# damage to electrodes when initially installed,

# likewise, damage to the insulator.

# mixture or oiling problem can cause carbon deposits to form on the insulator tip allowing the spark to track across to the earthed body of the plug.

# dirty finger marks on the ceramic insulator allows the high voltage to form a carbon track to the earthed shell.

# gap too large makes it more difficult for the spark to jump across, causing high tension components to try and build up a larger voltage before the spark will propagate. This increase voltage may try to seek an alternative route to earth causing carbon tracking path down the insulator or across the insulator tip.

# damp or indeed water close by the plug cap either quenching the spark or causing local tracking and eventually croaking the spark plug.

Perhaps others too?

Read all about the whole shocking ignition story from here

http://www.vintagemodelairplane.com/pag ... ion04.html

and here

http://www.vintagemodelairplane.com/pag ... ion05.html