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Re: boost has major swings Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Wed, 27 Jun 2001 08:12:19
In Reply to: boost has major swings, rob  [Profile/Gallery]
, Tue, 26 Jun 2001 22:38:13
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I assume that you plug the hose when you pull it off, and that when you pull the hose off the center post, you can get full boost.
Frankly, it sounds like the APC is kicking in and reducing boost. From memory, the center post is the C "charge" line - it has the intake manifold pressure. What you're doing is essentially taking the pressure signal away from the wastegate actuator. I'd expect you'd get the same effect if you pulled off the W line - the one to the wastegate actuator. That actuator is what limits boost. In fact, you pull that line off, and you should be able to boost well into the red before the fuel cutoff kills the engine and puts you into the windshield.
The APC would kick in if it detects knock. Now, that could be due to a faulty (loose) knock sensor or bad motor mounts, but the most likely cause is that the engine is knocking. First off, try running a tank or two of higher octane gas. If you're not running premium, then spring for the extra $$ and try it. If that fixes the problem, then you know you should be running higher octane fuel.
You don't mention what year/engine you have, so the next part is guessing. If you have a non-DI car with adjustable timing, check the timing. Too advanced can cause knock. Check for vacuum leaks - lines cracked or fallen off. A vacuum leak will cause the engine to run lean, and lean running, especially in hot weather, makes an engine more prone to knock. Make sure the spark plugs are the right type, gapped properly. When chasing down engine problems, always get the plugs specified in the manual. Saabs, especially DI-equipped, are VERY sensitive to spark plug types. Get the ones specified, not what the parts-counter guy at AutoBazzar cross-matches to. You can play those games when the engine is running right, not when chasing problems.
After that, it gets more interesting if the engine is still knocking. You'll want to know if it's running lean, because after chasing down all the vacuum leaks, it could be a faulty fuel pressure regualtor, weak fuel pump, lazy O2 sensor, or mis-adjusted AMM (depending on year).
But first, look for loose hoses and put in some 93 octane (US), and go from there.
, Tue, 26 Jun 2001 22:38:13, Wed, 27 Jun 2001 08:12:19 <-- Viewing This Message, Wed, 27 Jun 2001 18:50:41
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