snap, crackle, pop and bang

Barry · Post by **Barry** » Mon Aug 13, 2007 8:09 am

Another quick check if you've got enough length on the leads, is to swap the plug and lead from a 'bad' cylinder over with those from a 'good' cylinder (obviously swapping them on the dizzy cap as well).

If the problem moves to the previously 'good' cylinder, you know it's the plug or lead, if the problem stays put, you know it ain't

.

I suppose after this stage, you'll be back onto fuel type checks again?

Barry · Post by **Barry** » Mon Aug 13, 2007 8:17 am

BTW Tim, when you are checking the spark how are you doing it?

I'm sure you know, but checking for a spark outside of the engine with a normal plug gap doesn't mean very much. I keep a plug with the gap opened right out to 1/4 or it might even be 1/3rd inch. If you get a big cracking spark across this sort of gap, you know there's plenty of power there.

On the other hand, if it won't jump this, but will jump a normal gap, you know you are well down on sparking power, and there's every chance that the spark is intermittant under compression. I had an old BMW E21 323i. One day this failed to start at all, and would just give the odd cough. Seemed to have a spark on all six. In the end, someone suggested I tried with a wide plug gap, and the spark dissapeared.

Turned out that it was a loose wire on the ignition amplifier, and I kept messing around until all of a sudden, the spark started jumping 1/3 inch easily, and the car started again.

timmyboy · Post by **timmyboy** » Mon Aug 13, 2007 9:17 am

If there was a problem with the idle jets would this not mean a shortage of fuel and I'm sure that's an issue! Also it will pop and bang on idle or with the throttle open. The valve clearences were only done about 1000 miles ago so I'm hoping they're okay, I haven't checked them again. But, would this cause it to work sometimes and not others? Also I did swap the plugs in 6 and 4 when I changed the leads, this is when it worked for about an hour and then stopped. The plug in 6 was a bit sooty but if you wipped it off it did look like it was brand new and the others showed some sign of use. I don't know if there is a build up of fuel on the plug.
This brings me to another ameture hour question. Can you buy a proper plug spanner with a fixed extention that will actually fit into 6 and 3. I'm using a socket and extention and it's a bit hairy thinking the socket might stick to the plug and come off the extention. So as a result I'm a bit slow taking the plugs out so I don't know if the fuel has evaporated.
I did try it with a opened up plug but nothing like that much so I shall try that.
It also seems to have know a small hole in the heat exchanger (they've seen better days) where it keeps banging on that side, so I think I shall have to look into replacing these now!!

Thanks for all you suggestions.

Gary71 · Post by **Gary71** » Mon Aug 13, 2007 9:45 am

Hi Tim,

Certainly sounds ignition based, a weak spark making the plug foul up, making the spark weaker until it eventually goes out altogether.

Can you put your old HT lead back on?

For the plugs I use a 1/2" drive plug socket with two universal joints taped onto it. Easy access and it gets over the losing the socket fear, which I did once and it took me two hours to get the bugger out!

timmyboy · Post by **timmyboy** » Mon Aug 13, 2007 10:20 am

I will try the old leads.
Thanks Gary, I feel a bit less of a tit about the plug spanner!