Zeke, a few comments about your post:

- I think you mention that DI failures were (are) a serious warranty concern for Saab. If changing the plugs at least every 15K miles alleviated the failures, why does not Saab makes this recommendation ? A plug change even at the dealer would be under $ 50, but when the DI fails under warranty and must be replaced, the cost with towing, parts, etc. must be 8 times as high. Less DI failures would save Saab money, as well as prevent some of the DI failure frustration experienced by owners.

- The capacitive discharge circuit utilized in the Saab DI operates under different principles that a transformer used for instance in a neighborhood power distribution circuit. There is a direct correlation between level of load in the secondary and power intake in the primary, the higher the load, the greater the heat. In a capacitive circuit, the capacitor can only charge to a fixed level, and when the ECU closes this circuit to the primary of the ignition coil(s), the capacitor dumps the charge into the coil. Given that a discharge occurs in the secondary circuit outside of the coil windings, the resistance of the secondary has negligible impact on the power draw of the primary, as the capacitor discharges in mili seconds and this circuit opens to allow the capacitor to charge for the next firing cycle. Running at high RPMs would produce more heat in this circuit.

So I believe heat to be cause of the DI failures, but caused more by just the location of solid state circuits atop the engine than plug gap. I would suspect a smaller plug gap allows a higher voltage reading to the combustion module, indicating more favorable combustion chamber conditions, and if you are running higher octane fuel you'll get more boost and spark advance, and more power.

So I think maintaining proper plug gap keeps performance consistent, but I'm not at all convinced that wider plug gap causes the electronics to work harder in any meanfull way.

Saab is the only production manufacture to use a capacitive discharge ignition system, these systems are both costly and have had reliability issues.

posted by 204.32.20...

• Spark plugs--intervals --sharp edges, TG, Mon, 14 Jul 2003 14:09:59
  • Spark plug report, Jason 0W-40, Mon, 14 Jul 2003 22:13:20
    • Re: Spark plug report, TG, Tue, 15 Jul 2003 03:06:31
      • Re: Spark plug report, Jason 0W-40, Tue, 15 Jul 2003 08:36:20
        • Re: Spark plug report, TG, Tue, 15 Jul 2003 20:07:54
  • Covered at 20K Check-up?, Chuck, Mon, 14 Jul 2003 21:07:45
    • No. n/m, J, Mon, 14 Jul 2003 21:41:34
  • any advantage..., Jason 0W-40, Mon, 14 Jul 2003 18:38:07
    • Re: any advantage..., Dean, Tue, 15 Jul 2003 06:20:32
      • Question about spark plug threads, Jason 0W-40, Tue, 15 Jul 2003 08:57:47
        • Re: Question about spark plug threads, Dean, Tue, 15 Jul 2003 10:15:49
      • Re: any advantage..., Jason 0W-40, Tue, 15 Jul 2003 08:34:36
  • Re: Spark plugs--intervals --sharp edges, Jason 0W-40, Mon, 14 Jul 2003 17:08:18
    • Re: Spark plugs--intervals --sharp edges, TG, Mon, 14 Jul 2003 18:37:21
      • Re: Spark plugs--intervals --sharp edges, Jason 0W-40, Mon, 14 Jul 2003 18:46:57
        • Re: Spark plugs--intervals --sharp edges, TG, Mon, 14 Jul 2003 19:53:23
  • Re: Spark plugs and DI's (long), zeke, Mon, 14 Jul 2003 15:22:32
    • Re: Spark plugs and DI's (long), dtech, Mon, 14 Jul 2003 16:49:33 <-- Viewing This Message
      • Re: Spark plugs and DI's (long), zeke, Tue, 15 Jul 2003 07:52:14
        • Re: Spark plugs and DI's (long), dtech, Tue, 15 Jul 2003 09:52:18
        • Re: Spark plugs and DI's (long), dtech, Tue, 15 Jul 2003 09:50:59
          • Re: Spark plugs and DI's (long), zeke, Tue, 15 Jul 2003 12:05:10
      • Re: Spark plugs and DI's (long), Dean, Mon, 14 Jul 2003 19:30:32
  • TG ... neither this post nor your post on 9-3 BB is ..., J, Mon, 14 Jul 2003 14:45:20
    • Re: TG ... neither this post nor your post on 9-3 BB is ..., Dean, Mon, 14 Jul 2003 19:32:31
      • Re: TG ... neither this post nor your post on 9-3 BB is ..., TG, Mon, 14 Jul 2003 19:54:53
    • Re: TG ... neither this post nor your post on 9-3 BB is ..., TG, Mon, 14 Jul 2003 18:11:18

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