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Re: Overboost! Boosted to end of red last night! Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Thu, 16 Jan 2003 13:20:27 In Reply to: Overboost! Boosted to end of red last night!, terraplanem, Thu, 16 Jan 2003 10:13:13 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Boost is controlled by the wastegate actuator. Under high boost conditions, the pressure pushes the actuator against its spring, and the rod on the end moves. This pushes a lever under the turbo, which causes the vanes in the turbo to open, dropping boost.
All the APC does is determine how much boost pressure gets to the wastegate actuator. Under 'base' boost, the APC delivers all the boost pressure to the actuator. Under 'full' boost, the APC solenoid is activated, and it opens and ports a small amount of pressure from the actuator. Since not as much pressure is making it to the actuator with the APC solenoid energized (full boost), it takes MORE boost to get the actuator to move and close off the turbo.
The APC box can only keep the APC solenoid off, or fully energized. (In some systems, in-betwee). But at fully-energized, you should get no more that full boost - end of yellow/beginning of red. So the knock sensor, or APC box, can't give you overboost.
Most likely problems - (1) the hose from the APC solenoid to the wastegate actuator has fallen off, or has cracked from heat and is leaking. (2) The wastegate actuator is stuck. (3) the pressure hose from the intake to the APC solenoid is off, or leaking.
Basically, you want to know that the air pressure makes it from the intake manifold, to the APC solenoid, to the wastegate actuator, AND the actuator moves. With a cold engine (try this hot, and you'll have scars to tell your grandkids about), reach under the turbo. You'll find a little lever with a rod on it - the rod goes to the wastegate actuator. You should be able to pull the actuator rod out from the actuator a little - only about 1/4 to 1/3 inch or so, against the spring tension. Not a lot of movement, but there should be some.
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