1999-2009 [Subscribe to Daily Digest] |
they have been that way for DI equipped cars as TG pointed out. The plugs from my other car, a 9K Aero, always look clean and nice after 20K miles but I always get this mild hesitation after 10K miles or so. The appearance of the plugs is exactly what Dean has described in his opening paragraph, and this is on a 9K.
Given that the stock 9K plugs are inexpensive, about $10 for four, there is little point in regapping or cleaning the plugs if I have pulled the old plugs. I just put new ones in. This topic has been discussed often in the 9000 board.
I would imagine it is hard for Saab not trying to post a long plug change interval as other car makers tout no tune up for 100,000 miles. This goes real well with my frequent rant on life time coolant, and other fluids as well.
Wife's 9-5 Aero has less than 5K miles, I won't bother to look at that thing maybe in another 6 months. The 9-5 Aero plugs are more expensive but they are about what someone would charge for an oil change. So I would probably do the same, i.e., put in new plugs.
I put dielectric grease on the plug insulator/rubber surface. You can find those in automotive stores. Don't have to use too much, just a thin coating would suffice.
As for not turning the DI upside down, I don't know about the black DIs, but the oil in the red DIs are not very viscous, so they flow to the lowest point with minimal time. I see no reason in keeping it right side up when not in used or just for a short time. I do see the point of not using it upside down and putting spark plug into the rubber boot to test the DI (maybe ok a few ignition cycles) as the oil would be sitting in the wrong spot.
As for whether engine performance is related to wearing down of plug electrode's sharp edges. I would imagine the edges may look sharp at the macroscopic scale but may be dull at the microscopic scale. So the very gradual decay in performance may very well due to the gradual rounding of sharp edges with each discharge. I would think spark plug and car manufacturers spend millions reseaching this, or at least I hope :-).
As for the frequent loosening of the DI hold down screws, I would guess they have been that way since DI was put on these engines. Given the constant shaking the DI is subjected to, it would hard to imagine the screws don't work themselves loose one way or another short of using loctite. I just take that as part of routine inspection.
Thank you Dean for your thorough report.
posted by 12.89.1...
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