Re: Vibration under acceleration. Spark plugs... - Saab NG900 & OG9-3 Bulletin Board - Saabnet.com
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Re: Vibration under acceleration. Spark plugs...
Posted by Doug P (more from Doug P) on Thu, 12 Dec 2002 14:21:30
In Reply to: Vibration under acceleration., Todd [Profile/Gallery]
, Thu, 12 Dec 2002 08:42:37
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To explain my previous response a little better to mb's post, air pressure has a direct effect on the flow of electricity. When you try to greatly increase pressure in the cylinder with a turbo it degrades the ability of the spark to jump the gap. This is why there was discussion a while ago on closing the gap to as little as 0.9mm. NGK's that I use -BCPR7ES-11 are gapped at 1.1mm (the 11 in the number) I closed mine down to 1.0mm and haven't felt the need to go to 0.9 as I don't really bury my right foot (alot)lately. I do remember reading something about Saab engineers,or perhaps it was NGK people, saying it was safe to close the gap to 0.9mm. Now, on the DI cassette, it's bad not to discharge that spark which, it was explained, was a very probable cause of frequent failures. Keep in mind, now that it's winter, gaps will tend to open up with more extreme cooling and heating. It never hurts to check. I know this didn't seem a likely cause at first. I too thought I was loosing an axle it was so violent, but as soon as I backed off the vibration was gone. Of course this doesn't rule out balance problems in the drive line but we know you should, for the most part, have vibration all or most of the time if it were an imbalance problem. I'm no engineer and I'm sure there's techies here that can explain/expand on what I present. I have, however, had this experience on two Saab turbo's and consulted with people I trust (Rob at Scanwest Autosport)and the plug replacement eliminated all vibration/missing. Best of luck to you.
Doug Saab since'75 86 9000t, 99 9-3
posted by 216.40.23...
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