All fixed!!!

[zhastaph]

She's all fixed

I changed the coil pack on the right hand bank & all 8 HT leads with a set of magnecor's and she's now running like a dream.

I've also done the plugs and new K&N air filters whilst I woz at it.

=====================

Initially I thought it was the coil pack that had failed given that 2 cylinders were firing poor on the right hand bank, they share a common coil {wasted spark} so it seemed a logical assumption. However in hind sight and having read more about the technology it seems that a failed HT lead will also affect it's brethen's spark also. I'm gonna draw a diagram on how this works sometime later if anyone's interested.


Thankyou everyone for your helpful input.

Col

[GKP]

Splendid news (but I bet it wasn't the cheapest of "simple" fixes!)
Time to start terrorisng the locals again

[zhastaph]

GKP said:

but I bet it wasn't the cheapest of "simple" fixes!

£95 for a set of HT leads, £95 for the coil pack, I also did the 2 filters at about £70 for the pair plus there was the gaskets and stuff. I cant remember whether there was VAT on top of that an all, so prolly about £300. Not the end of the world, she's worth every penny .... just as long as she don't keep on breaking


Anyway, I'm one of these people who has to know how everything works. Knowing how something works is halfway to fixing it when it breaks.

I was curious how the coil pack worked, I was told that each coil pack only had 2 coils and each coil fired 2 cylinders simultaneously. The v8 Esprit as 2 coil packs, 1 pack for each of the banks. When the spark fires, 1 of the 2 cylinders is on it's compression stroke and the other is on it's exhaust stroke, this second spark serving no purpose.

When I found out that the 2 cylinders on my Esprit were sharing a common coil on the coil pack I immediately assumed that the coil itself must be faulty and so decided to replace the coil pack as a fix. But it looks more likely that it was simply one of the 2 HT leads that was faulty.

I've drawn a diagram;

{please don't laugh I am no artist by any stretch of imagination}



The coil in the coil pack works like any normal transformer. It has a primary winding that is connected to the ECM and a secondary winding that has an input from one spark plug and it's output on the other spark plug. The spark actually starts at the engine, leaps the gap to the electrode of the first plug, travels up the HT lead, through the coil pack, down the next HT lead then leaps the gap from the electrode of the plug to it's casing where it ends it's life back on the engine.

Thus a breakdown of 1 HT lead will not only reduce the quality of spark at it's spark plug but will also reduce the quality of spark at it's brother's spark plug by the same amount.

This is also why in the service manual it tells you to ground the HT lead on the engine when you are pulling HT leads off of spark plugs to test for misfiring cylinders - removing an HT lead without grounding it will mean that you will also get no spark at the other plug.