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Hi guys,

So my '89 has a swedish dynamics box, 3 bar FPR, and bigger injectors. If it matters, it also runs a cooler thermostat and generally operates at 1/4 on the stock temp gauge. Different from stock C900 turbos Ive owned in the past, this APC seems to almost never cut boost, and will boost regularly and smoothly to 15 PSI.

Because other 900s Ive owned seem to cut boost at different times, I wondered if the wastegate was sticking closed. I uplugged the APC and I was glad to see Boost was fixed at 5psi, which leads me to believe the wastegate is in fact functioning correctly.

Is this a safe assumption? It just seems weird that the apc has never cut boost (in the two months Ive owned it), except at the cutoff at 15psi.
 

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Set up a knock light. Test out the knock circuit and verify that it hasn't just been disabled on the APC.

The SD APC is tweaked to allow and hold more boost and still keep knock detection. That is its purpose.
The bigger injectors and 3bar FPR should allow the system to provide enough fuel to make the higher boost levels possible without regularly knocking.

If you are getting 15psi, you're knock sensing circuit works, and you are not getting knock, you should be golden. That's how its advertised to work. Its why you would buy the SD APC kit to begin with.

If you are getting solid 15psi and you are getting knock without boost cut, then something is broken and you are on your way to blowing something up.
 
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