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'90 T16 Convertible - Boost issue
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Posted by Jeff Cullen (more from Jeff Cullen) on Wed, 19 Aug 2009 00:02:18 Share Post by Email
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Hello Gents,

I've been trying to help my buddy with a boost issue... he rarely seems to get more than base boost. I have seen it spike a bit over base but only very briefly.

First, we tried swapping parts from a car with known good boost:

-APC solenoid
-knock sensor
-APC brain

This didn't solve anything. We tried the screwdriver test on the knock sensor, and the solenoid performed as expected.

We then tried pulling the wastegate hose from the APC solenoid and went for a cautious test drive. Wild boost into mid red up to fuel cut, with zero audible knock.

At this point, the only ingredient left seemed to me to be the pressure transducer. To test the theory, I unplugged the vacuum hose from the intake manifold which goes into the cabin and splits to the pressure transducer and APC/turbo gauge. I then ran a vacuum hose from the intake manifold straight to the boost gauge. Unfortunately when we did this, the car was running on 87 octane petrol, however we got consistent spikes to very near the red, then good taper and modulation above base boost, as one would expect with the normal 599 APC box.

We pulled the pressure transducer from a car with known good boost and after considerable swearing and knuckle-bashing, went for a test drive... only to find we were back to square one!

His fuel tank is almost empty and I've instructed him to FILL UP with 94 octane petrol.

I haven't checked anything to do with the cruise system or brake/clutch switches, however I would have expected no more than base boost even with the pressure transducer out of the picture in such a case, as I would figure APC would leave the boost control solenoid wide open...?

Any pointers at this point would be much appreciate, we are really banging our heads against the wall on this one!

Cheers,
--jeff

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