Spark strength, how strong / far? Plugs.......

[berni29]

Hi All

Apologies for this post in that it is a bit rambling, but I would be interested in any opinions on the following:

I have a suspicion that my ignition system is not performing as well as it should. I have swapped every part out at some point, including the whole system at once, including the distributor cap and leads, but my spark just never seems that strong. I have tried points and Lumenition (currently on the car).

My suspicion about the system was renewed this weekend when on taking my car for an MOT it behaved very well in warm weather in heavy traffic, and on the open stretches of road for about 40 minutes, and then started misfiring heavily to the point of being undrivable. On inspection (at the MOT garage) the plugs were heavily fouled. Sooty and black. The mechanic said that it was because the plugs were not the standard NGK type, and that the spark was too small due to te small plug tip. They were BCPR6E-11 platinum tipped from a Nissan ZX 300 twin turbo. I had fitted them because the car seemed to run better with them rather than the BP6ES that I would otherwise use. Is it normal for plugs to be fine for 40 minutes of mixed driving and then foul all of a sudden? I am thinking that the spark weakened and that caused the misfire and fouling.

If I hold a spark lead end near a cam cover nut I can get a spark to jump about 1/4". That is with a (old) Lucas sports gold coil (oversize). I have tried other coils. Always old ones never new though.

My brother's spitfire can get a spark to jump about 1/2", so I have been using that as a benchmark. How far should a spark jump?

I have 12v feed at the coil, so to see if I could improve things I fitted an old ballast coil. I can now get the spark to jump 1/2". I know that the coil life will be shortened, but does anyone know what a likely life would be?

Many thanks for any opinions

Berni

[john.p.clegg]

Berni

Knowing Lotus electrics,have you measured the voltage you're getting at the coil?
I once did this for my yellow headlights and found 9Volts,replaced feed via relays got 12volts and nice bright headlights

John

[berni29]

Hi John

I am getting a good 12v at the coil. It is possible that the spark is fine and I am imagining the whole thing! The headlights used to be awful, but after much earth cleaning are now fine. I do get a very slight dimming of the sidelights in time with the indicators flashing, so everything is not perfect. The headlights used to go out when the electric windows were operated, and that does not happen anymore! In fact I am going to order some 7" units that take the H4 halogen bulbs today.

I am told that they are a massive improvement.

All the best

Berni

[tdafforn]

Have had plug fouling problems in the past..
Tried a range of makes and temps of plugs until I found some that worked.
My problem was exacerbated by the engine being on its last legs resulting in a fair amount of oil getting on the plugs.
One other thing I found was that if I spent a session fiddling with tuning the engine. Then left the car for a couple of days, then ran it, the plugs fouled (probably not really getting the engine to temp). On the other hand, I did a 600 mile round trip to Goodwood and not a sign of fouling (nice brown tips)
Cheers
Tim

[curly type 26]

Hi Berni, What leads do you use? Particular note with lumenition from esprit manual do not use resistive leads with resistive plugs it causes the plugs to foul and fail i had that symton years ago on my esprit when supplied wrong plugs it would cut on 3cyl then 2 i stopped and cleaned would be okay again but very shortly same story changed to correct plugs and rocket ship perfomance back. i would also check all earth points it is good to have 12v supply but if you have high resistance earth path it wont be much good get your meter out and take a few readings. Hope this helps Colin.

[berni29]

Hi There

I will try swapping the leads out and do some spark jumping tests to try to get a handle on which ones perform best. Strangely enough in the past I have found copper leads to be best even though they are the oldest technology wise.

Berni

[berni29]

Hi There

I have been doing some testing and looking at leads, and the one from the coil to the distributor had 18k ohms on the side, so i have swapped that for a plain copper lead. I tested various leads and the copper one gives a fatter much whiter spark, while the silicone leads give thinner more gold coloured ones which can jump slightly further. Maybe I should swap all the leads for copper ones? The existing silicone leads do not have any ohm ratings on the side, just a BS rating.

Anyone know why the spark looks so different from the copper lead? Also the coil gets ultra hot. Is that normal?

Berni