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Old 04-10-2012, 11:58 AM   #18 (permalink)
EcoModding Learner
Join Date: Feb 2012
Location: Hendersonville, Tn
Posts: 63

nonikname - '99 Saab 9-5 2.3t
90 day: 33.71 mpg (US)
Thanks: 6
Thanked 8 Times in 7 Posts
I'll stir this pot a little more lol
In my Saab,
The system puts a low voltage over the spark plugs when they are not fired to measure ionization in the cylinders. The ionic current measurement is used to replace the ordinary cam phase sensor, knock sensor and misfire measurement function.
Saab Direct Ignition - Wikipedia, the free encyclopedia

So yea, some of us have to use the recommended plugs.

But I also believe that wear in the engine, age, modifications, and other factors may be considered.
After changing plugs many vehicles, I believe that indexing works for some cars, but not all. The gain for me was quite small, but the cost was small too - only 1 extra spark plug. Neither gains nor cost are enough to argue.
1999 Saab 9-5 sedan 2.3t 5speed
2013 prius 3

"God is a God who both created the universe, and also had a plan that included me as an individual human being. And that he has made it possible for me, through this series of explorations, to realize that. It is not just a philosophy, it is a reality of a relationship. "
Francis S Collins - director of the National Human Genome Research Institute
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