How many cylinders do you need?

[leadfootlydon]

I seem to have a spare cylinder or two in my Stag.

For the first time in years, she let me down this afternoon. Pootling along, she just cut out. Tried a few times to restart, but no joy. Poke around a bit under the bonnet, nothing obviously wrong, but after maybe 5 mins she fires up OK. Drive 200 yards and same again, doh! Only this time she won't fire up again.

This is where it gets very odd.

Following the old 'spark and fuel' diagnostic formula led me to pull the HT lead off #1 cylinder while girlfried cranked her. Damn thing fired up first time (with me holding the HT lead). So switch off, reconnect HT, and she's sulking again (car, not g/f) - no hint of wanting to fire.

Unplug #1 HT again, and she starts! Sod it, we'll drive home like that! The car ran no problem on 7 (or maybe 6, or 5, or....?) cylinders. Obviously not quite as smooth as normal, but not nearly as rough as I would have expected.

It was dark when we got home, but would anyone like to suggest where I start looking for the cause?

Coil? HT leads? Lumenition? Dizzy? Plugs? Alternator? Battery? Maybe even something mechanical?

[fat richie]

Fecked plug?

[dougc]

Process of elimination I'd say. Work from the spark backwards i.e. replace the plug, then the lead etc. Good excuse for a Sunday of tinkering under the bonnet...

[leadfootlydon]

fat richie said:

Fecked plug?

I guess you mean somehow that I got lucky by disconnecting a plug that was somehow causing the other plugs not to spark? Is that possible?

Or could it be that somehow with that HT lead connected and the plug sparking it was unbalancing something else and causing the engine not to run?

The odd thing is that the car seems to either run OK, or not at all. It's not like you hear sometimes a car that briefly fires but won't run properly.

[leadfootlydon]

dougc said:

Process of elimination I'd say. Work from the spark backwards i.e. replace the plug, then the lead etc. Good excuse for a Sunday of tinkering under the bonnet...

Thanks. I'll give it a go. Plugs first.

Is there a way to test HT leads or should I just buy news ones? These are about 4 years old; done about 5,000 miles maybe. (3rd car, summer use, work from home)


Edited for typo

Edited by leadfootlydon on Sunday 3rd December 00:33

[F.M]

Looking in the engine bay at night ..you can sometimes see it sparking/earthing against anything where there are tiny splits...best to replace them as they are cheap and easy to do...replace 1 lead at a time so you don`t get in a muddle...

[leadfootlydon]

F.M said:

Looking in the engine bay at night ..you can sometimes see it sparking/earthing against anything where there are tiny splits...best to replace them as they are cheap and easy to do...replace 1 lead at a time so you don`t get in a muddle...

Brilliant idea. (But not tonight).

[LewisK]

[quote]Is there a way to test HT leads[/quote]

Yup, just move the lead to another cylinder, see if the problem moves with it.

Worth replacing them with decent ones if they're unknown, anyway

[Sporting Bear]

From personal experience on a couple of V8s I would strongly recommend replacing the leads with high quality leads as V8s get very hot under the bonnet and if you get really good set they could last 10 years

I would also strongly recommend changing the rotor arm and distributor cap they're not expensive but tend to be forgotten and can make a big difference even if they look OK, be very careful to keep the leads in the right order as you know a V8 will run even if they're not in the right order

When I buy a classic amoungst the first items I change are the leads, I broke my rule own rule with a V8 I had, it just cut out on me for no reason, a couple of times, but restarted perfectly, I took the car to a tuner - it was a faulty lead!

[leadfootlydon]

Sounds sensible to me.

These leads have been to Spain and back, so maybe it is about time I changed them.

Out of interest, just how does a faulty lead cause the engine to stop?

And, following on from that, why when I left the lead unplugged did the engine start and run OK?

[Sporting Bear]

Well with mine the spark caused havoc in the dissy cap I think the car had an ECU so that probaly didn't help

Taking a faulty lead off means the other seven may not have "gotten confused" (shorting out in dissy cap)

I once mixed up two leads on a V8 and I only really realised when I put my foot down hard

I went on a tour and on the second morning my car went the best it ever had, by the afternoon I felt that I was down to seven and a half unlike above, so it can be an unlucky combination of things - turned out to be a "heat shield" connector between the lead and plug

Edited by Sporting Bear on Monday 4th December 13:23

Edited by Sporting Bear on Monday 4th December 13:26