Sooty Plug SORTED

[john.p.clegg]

Dear All

Just need a second ( or third,fourth etc.) opinion re. a sooty spark-plug,if we disregard the fuel aspect for the moment, ie running rich , can a misfire cause this?. If the gap was too large could the spark be "blown out" and would this result in a sooty plug?

Thanks

John

[Elanintheforest]

I've only just resolved this issue on my Escort Twincam, ands the change has been remarkable.

The car has always spat-back through the carbs on a very light throttle, but otherwise was fine. I'd always assumed that this was an issue with the carbs. This year, after the winter slumbers, the engine started to misfire a lot after 15 minutes or so, and pulling the plugs revealed that they were very sooty...not oily.

In the past I've always found that this is down to the coil or condenser starting to break down, so I ordered up a new ignition set from the Distributor Doctor.

I fitted the coil first (nice and easy) and the spit-back that the car always had was cured. I was chuffed to bits, but after 15 minutes, it started to misfire again, and I crawled home on a very light throttle in 2nd...as fast as it would go!

I took the distributor cap off to reveal a Luminition Magnetronic unit inside, so no points and no condenser! That was a bit depressing as I KNEW it was the condenser that was failing. So I put the new rotor arm in anyway, took it for a spin and it's now fine. No misfiring, no spitting back, and no sooty plugs.The car is running better than ever, and I guess that it had a double fault with both the coil braking down, and the rotor on it's last legs.

All 4 plugs were sooting up, but I guess that if only one of yours is, then it could be down to the cap or lead / plug cap for that cylinder.

Read up what Distributor Doctor says about the repro coils, condensers, rotor arms and caps....and get a set ordered up!

http://www.distributordoctor.com/

Mark

[john.p.clegg]

Thanks for the speedy reply Mark but hasn't done me any good as I have EFI fitted with wasted spark...

John

[Elanintheforest]

I think that the fundamentals apply John....a misfire can cause sooty plugs!

I also changed from NGK 8 with a 25 thou gap to NGK 6 with a 35 thou gap...the increase in gap once I knew that I had the luminition fitted.

I still get very confused regarding which plugs to fit, so in the tool kit I'm carrying 6, 7 and 8 plugs! The engine is quite tweaked up, with L2 cams and polished ports, but it probably needs to go on a rolling road to get properly sorted.

Mark

[rgh0]

Hi Mark
The Lucas cap and rotor struggle to keep up with the extra voltage created to fire across a larger plug gap and can breakdown. Personally I would leave the plug gaps at 25 thou.(or change to a Bosch distributor)

Unless your driving continually at over 5000 rpm I would run the NGK BP6ES. 7's if you are running hard on motorways all day or maybe if doing a track day. I use 8's in my race engine running 12.5 comp ratio and running at 8000 rpm and full throttle and they are almost to cold, I suspect I would be OK with 7's

cheers
Rohan

[Elanintheforest]

Thanks for the plug summery Rohan. The 6s seem to be working well, and the coil is an American Petronix unit which are meant to be bullet proof. I don't trust any new Lucas stuff any more!

I'll take the plug gaps down a little and see what happens.

Mark

[john.p.clegg]

Back to the sooty plug, after checking again,found suspect wiring on No1 injector connector and TPS sensor connector, (home-made loom with Mondeo connectors ) suspect sticking injector on No2...after changing/sorting it's back to Good..

Had to brake sharply on the M67 as a Police Range Rover came into view...110mph at 4800 rpm is not bad going..

John

[rgh0]

I can hear the testimony now in court....

"No m'lord the speedo on the car was only indicating 110 mph like I wrote on LotusElan.net
you know Lotus speedos are notoriously optimistic... its what Colin did to impress the punters"

cheers
Rohan

[john.p.clegg]

Come on Rohan,I didn't say I was doing 110mph,just that co-incidentaly a dog ran across the Motorway as a Police Range Rover came into view, and any old car that was capable of 110mph at 4800 rpm would be doing well...

John

[gav]

I have an irritating misfire that I have failed to cure and is driving me to switch to efi.

Went for a run last week and came back on a horrible misfire after 20 mins.

So far I have replaced plugs (I am running 7s because I do drive quite hard), the leads, cap and rotor arm. I am running an Aldon igniter so no points to worry about.

The only thing I haven't changed is the coil which must be around 20 years old by now. A Bosh blue one.

How do coils fail when they expire and coud this be the source of my sorrow?

Thanks
Gavin

[john.p.clegg]

Have you thought of fuel??

John

[gav]

John

Good point - I am running the modern version of Shell Optimax with the millers octane booster. It could be a bit rich and I could add some straight Optimax to thin it out a little...

Gavin

[john.p.clegg]

Gav

Get yourself down to Tesco and get some *** in it...

John

[EdHolly]

If you ever see a hint of rust on the spigot where the rotor button lives on top of the rotor arm - suspect the rotor button is breaking down. The spark or a potion of it is finding its way to earth down the shaft instead of along the spark plug leads. This then heats up the end of the shaft and burns the small amount of oil there and it goes a bit rusty as a result. Can only remember 3 occasions when rotor buttons have let me down - and one of them was a brand new one.

Fixed my sooty plugs with much fiddling with the jettiing on the 40s plus drilling the butterflies with a tiny hole each. -31's Pull the plugs anytime now and they are almost white with a hint of colour. But still just occasionally (once an hour say) get a bit of a stumble going through 1800rpm but happy to live with that. I use NGK 6's and drive it as you would a daily driver.

Ed