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Base boost Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Fri, 29 Jul 2005 05:17:16
In Reply to: turtbo seems to be weak, kenjrbanga, Thu, 28 Jul 2005 21:27:43 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Boosting half-way to the yellow is base boost. If the APC system doesn't detect knock, it allows the full boost, which is the end of the yellow/beginning of green. If it detects knock, it cuts boost back to mid yellow. The car will still accelerate, just not as fast. Even on base boost a Saab is pretty quick. But as RS notes, not from a stop. Turbo engines don't produce much power at low RPM - the turbo needs to get going. And if you're limiting boost, it'll feel slower.
There are two major reasons for base boost - either the engine is knocking, or there is a problem with the APC system.
Do an archive search on Base Boost and you'll see a wealth of information.
First, go after knock. What octane fuel are you running? If you run a higher octane fuel, does the car boost better? If so, it's knock. Every car is different - some can get full boost on 87, others require 93. Run a tank of higher octane fuel and see if that helps.
Next - how is the timing set? Too advanced, and the engine will be prone to knock. Check the timing. Make sure the spark plugs are in good shape, the proper heat range, and gapped properly. WHile the plugs are out, look at the color. They should be a light grey. If they are really white, that's a sign of lean running. That can cause knock, and reduce performance. That can be due to one or more vacuum leaks, or reduced fuel pressure, either from a clogged fuel filter or a bad fuel pressure regulator (FPR).
If you've ruled out knock by running higher octane and tuning up the car, look for APC problems. THe most likely is the APC solenoid, that thingy on the radiator with three hoses and an electrical cable. That is the 'switch' that controls boost. The APC box provides power to it to get full boost - no power, base boost only. Check the connector is OK, hoses in place, etc. It may be an electrical issue in the wiring between the APC box and the APC solenoid. One place is the cruise control. When the CC is engaged, you only get base boost. There is a vacuum switch (on the right hand fender) that interrups power to the APC solenoid when the CC is pulling vacuum (engaged). If that switch is bad, you'll be stuck with base boost. But there are a bunch of others, from a loose connector on the APC box to a bad knock sensor, to just shot engine mounts. Again, check for Base Boost.
posted by 192.249....
, Fri, 29 Jul 2005 05:19:31, Fri, 29 Jul 2005 05:17:16 <-- Viewing This Message, Fri, 29 Jul 2005 05:23:37
, Fri, 29 Jul 2005 04:44:04, Fri, 29 Jul 2005 08:37:05
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