1985-1998 [Subscribe to Daily Digest] |
 | [Main 9000 Bulletin Board | BBFAQ |
Prev by Date | Next by Date | Post Followup ]
Member Login / Signup - Members see fewer ads. - Latest Member Gallery Photos
Re: Silly question about base boost adjustment? Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Wed, 22 Jan 2003 08:35:42
In Reply to: Silly question about base boost adjustment?, Trobinson9kT, Tue, 21 Jan 2003 23:56:31 Members do not see ads below this line. - Help Keep This Site Online - Signup |
When the engine is under boost, there is pressure in the intake manifold. That pressure is ported through the APC valve to the wastegate actuator. As the pressure increases, the actuator pushes against a spring, moving a shaft out. That shaft movement adjusts the vane positions in the turbo, affecting how efficient it is. More pressure, more actuator movement, cut back on turbo efficiency (pressure).
If the spring in the wastegate actuator gets tired, it'll be easier to move, so it will take less pressure before the turbo cuts back. Springs do get tired over time. Or the turbo efficiency has dropped some. I'll bet the slope of wastegate movement to turbo-boost drop off isn't linear.
And, of course, the boost gauge can get tired. It's just a spring at heart. Springs get tired, mechanisms gum up with dust and dirt, moving parts corrode, etc. And if there is a small leak between the intake manifold and boost gauge, you'll have good boost but the gauge will read wrong. The boost gauge is easy to check - turn the car off and look at the needle. It should point to the gap between the white and yellow. On a cold day with high barometric pressure, it'll be on the high side of the gap. But even if the gauge reads right with the engine off, a leaky hose to the gauge will still show up.
posted by 192.249....
, Wed, 22 Jan 2003 12:36:46, Wed, 22 Jan 2003 08:35:42 <-- Viewing This Message
No Site Registration is Required to Post - Site Membership is optional (Member Features List), but helps to keep the site online
for all Saabers. If the site helps you, please consider helping the site by becoming a member.
 |
 |
 |
 |
 |
