Spark Plug - Mixture Thoughts?

[jgerry2002]

'74 2002tii Metric Motor (2.2L), maybe 33k on the motor.

Ok.. so I've tried tuning with a CO meter, but not sure its quite right. I have not had a chance to install my mixture gauge yet.

Car seems to run pretty well for a couple of hundred miles then develops a misfire and loses power.

Any thoughts on the mixture?

All four plugs look the same, though there is slight oil usage which is apparent on the edges of the plug.

They are NGKBP6ES

They have maybe 30 miles on them.

Thanks,

[peteinjp]

What did the previous plugs look like?

The co meter won't tell you much if the car is not under load.

[Guest Anonymous]

that sooty black would make me think you are quite rich somewhere. Get the mixture meter on and find out since you have one.

[Guest Anonymous]

I would look to the coil. It will heat up with time and you could be getting a short. Therefor the misfire after a couple of hundred miles. If you have electronic points that may be the problem since they also heat up and who knows.

Re orient the coil with the terminals pointing up, that will cause the oil to cover the bottom of the coil windings and may cool things enough. I have also heard that if you mount horizontally either the + or - should be down. Any experts out there.

Looking at the plugs I would say you are OK on mixture.

Have fun

[TobyB]

Funny- I would have said rich...

t

[jgerry2002]

Ok, so you all see my quandry! Is it rich or lean?

It does a use a Crane optical ignition. Timing has been set with a light, valves are spot on at .006.

They are not the usual sooty (layered) black that is typical of any carb'd car I've seen when its running rich. Its sorta dark colored, but not layered.

This set of plugs looks to be slightly better than the last set, but I have not put enough miles on it yet.

The other plugs look more or less like that after 200-300 miles. Just sorta burned (maybe wrong heat range?)

I did not even consider a coil. Would a bad coil cause a misfire and actually ruin a plug?

[Beaner7102]

... Would a bad coil cause a misfire and actually ruin a plug?

Your coil produces the electricity that your Crane triggers a spark to each plug.

Bad coil would have a weak spark, sometimes no spark.

A weak spark would look like a rich mixture - not enough oomph to burn clean.

No spark - well no spark, no flame (misfire), and leave rich looking plugs.

Beaner7102

[peteinjp]

I'd guess that your mixture is all over the place. The plug is difficult to diagnose in this case. Supposedly you would need to keep the engine at a steady state of load and cut the engine to check the mix at that load. It's not easy to do esp WOT- which is most of what you need to know on the tii because you can only really make adjustments to the overall curve or just the idle. Having been thru this exact scenario with my tii cutting pluigs and revving the shit out of my car checking CO measuments (piles of spark plug photos to prove it) I HIGHLY recommend getting the wideband set up. It takes all the guess work out of it.

With the wideband i found that I was a little lean for power at WOT. I added fuel across the whole curve. i then made the necessary adjustments at low speed with finding the best spot for the throttle body cam relative to the pump and finally adjusted Idle. Of course this was after being sure the ignition was in perfect shape. Since then I haven't had to do a thing and it runs like a top after another 20,000 km's.

[penth2o]

Petinjp, What wideband meter are you using and were did you get it? thanks.

[peteinjp]

I use the LM1 from innovate motorsports. I bought it several years ago and aside from a bad sensor its been great. The guys at Innovate sent me out another sensor for free well after a year since I bought it. Good service!

[www.bmw2002.co.uk]

I have just fitted Bosch Super-4's & they have transformed the car. It starts better, runs cooler (really) & performance & economy have improved. I shall not be using anything else in the future. Seriously try them. I'm using WR78's in a 2002 Turbo which runs very hot. Here's some info: http://www.powersparks.co.uk/boschpage.htm