Re: Is it fuel cut out or spark cut out? - Saab Performance Bulletin Board - Saabnet.com
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Re: Is it fuel cut out or spark cut out?
Posted by Dean (more from Dean) on Fri, 11 Jan 2002 09:07:33
In Reply to: Is it fuel cut out or spark cut out?, nickR, Thu, 10 Jan 2002 23:08:14
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For the T5
The fuel is cut to limit boost or RPM's. When there is zero fuel, there is no combustion and there is no knocking possible. Zero fuel is not a lean mixture, it is no mixture at all. If only the spark is cut, there would be a nasty amount of fuel and air getting into the catalytic converter and this mixture could perhaps ignite in the exhaust manifold which would give the turbo and the boost quite a kick.
The ECU might be cutting the fuel and the spark.
With the T7 ECU the motorized throttle is closed a bit to limit boost. This is the soft fuel cut that prevents a MBC from increasing the boost pressure and thus the air mass flow rates. But a MBC can be used to quicken up the lower gears and to make the turbo spool up faster. I expect that the T7 can cut fuel at the RPM limits or other severe situations. The T7 may possibibly be faked out by electrical modification of the air mass sensor and/or the MAP. But that is only speculation. Such things are done on other vehicles and the ECU's use the 02 sensors to adapt. (The T5 MAP can be altered in this fashion... but there are issues that need to be understood when doing this.)
posted by 208.24.179.2...
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