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Discussion Starter · #1 ·
Im having boost issues now where im only getting base boost.

- Not the wastegate- Hooked direct pressure line and it will boost uncontrollable. Knock light works well.

- Apc solenoid functions. Clicks on start up and when brake is hit. Air flows accordingly through ports. When APC is unplugged with car ignition on the solenoid clicks.

So with that said it leaves suspect to the pressure transducer under the knee bolster. How do I check to see if it functions properly?
 

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Don't think the pressure transducer is causing your problem.

From Townsend; "Check the pressure transducer next. You will need a pressure gauge, an ohm meter and a Mity Vac. With the key on, disconnect the vacuum line going to the transducer at the manifold. Pump up .5 Bar pressure. The APC solenoid should chatter away. If the solenoid chatters, the APC control unit and the pressure transducer are working. To get deeper into the transducer, you will need to measure its resistance at various pressures. On 82 1/2 to 83s, disconnect the wiring to the transducer and measure directly off its terminals. On 83-85, measure the resistance at pins 8 and 9 of the APC control unit with the unit disconnected. On 86 up, measure between pins 10 and 23 of the APC unit with it unplugged. At atmosphere, the spec is 5-13 ohms. Then pump up a pressure of 1.0 Bar (15 psi) and let it off to .6 Bar (9 psi). The resistance should be 88 ohms +/- .5."

Full diagnostics here; http://townsendimports.com/Web/turbo_folder/baseboostdia.htm
 

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You have a knock light installed. Does it only illuminate when you disconnect the wastegate hose and have uncontrolled boost and at no other time? At what boost pressure does it come on?
 

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Discussion Starter · #5 ·
When I connected the wastegate directly to the intake manifold with no solenoid in between it lit up at 22psi. It also flickers when the solenoid is unplugged and plugged in.

I have a new development now.

I changed the apc to my spare and it boosted to 15 psi no issue but my rev limit went back to 5600 RPM where my chip is programmed for 7k. I unplugged the spare APC and the boost STAYED at 15 psi with rev limit of 5500.

THEN i plugged the APC back in one more time, went back to base boost and my rev limit went back to 7k rpm.

My spare APC might be bad as well because when i squeezed the case gently just right the solenoid would chatter away. so im still diagnosing.

Checked the pressure transducer and that does indeed work.

Im probably just going to go to MBC and use the apc as a knock detector for tuning. to hell with it but i would like to know whats going on.
 
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