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Re: base boost and pressure transducer test
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Posted by MS (more from MS) on Sat, 21 Apr 2007 23:21:14 Share Post by Email
In Reply to: base boost and pressure transducer test, 91SAABSE, Fri, 20 Apr 2007 22:45:08
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The test you did to check for p.t. lead continuity was correct. And the ohm reading at 9 psi indicates it is working, but the reading should be higher at 90 or more, not 55. Getting overboost when you jump the leads is correct as well. How the p.t. works: it's just a little rheostat which increases resistance to a circuit as the pressure increases, which tells the APC box to initiate the solenoid open/shut cycle to decrease pressure going to the wastegate valve control unit, thus allowing the wg to open and reduce the exhaust gases being circulated through the turbo unit, which then lowers the boost pressure inside your intake. With the p.t. lead wiring disconnected, the APC solenoid chatters away at a fixed cycle when the ignition is on. That's cuz there's infinite resistance. Connecting the two wires gives you no resistance, which ultimately keeps the wastegate shut tight giving you overboost. If your engine was hot and you did that test on the open road, you'd more than likely get tons of knock, which at that point (assuming your knock sensor was sound) the solenoid would begin chattering to reduce the pressure to the intake. The p.t. is there to help the engine avoid using knock as the sole factor in reducing intake pressure. Knock is damaging to the valves. I hope this helps shed some light.

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