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APC and Turbo Boost
Posted by Bob Jacobs (more from Bob Jacobs) on Thu, 11 Nov 1999 13:25:45
In Reply to: , Kok Chen, Sat, 17 Dec 1988 12:00:00 

According to the turbo/apc gauge in my 88 900T, I only get about 3/4 or 2/3
of boost. Needle does not border or go into red zone. Initially I suspected
that the car was in need of a tune-up - which it was. Replaced air and fuel
filter, plugs, plug wires, distributor cap, rotor and turbo bypass valve.
All of the work was completed by a Saab trained mechanic.

When the work was complete, the car ran better, but the needle did not go
any higher than previously. At this point, the mechanic took a known good
APC box - that he had already tweaked so that boost went into middle of red
zone. With this in the car, the gauge did indeed go into red zone.
Diagnosis - bad APC box.

So I find a used Red Box locally. This box is actually from an 87 9000, but
I am told by the mechanic that the box should work in the car. The person
who sold it assures me it is a good box. I install the box and now the
needle goes a little bit further than before, but still does not border the
red zone.

I have searched the TSN archives. There are several postings regarding
tweaking the APC box dating all the way back to early 90's. And, there are
several postings that describe the condition above, yet there are no direct
replies to this question. Do I have two bad APC boxes? Do I have old,
cracked vacuum lines that would effect this? Is the base boost set too low
(it is approximately at 4.5 PSI - this was checked)? Is the gauge not
calibrated? With the motor off, needle sits in broken white zone that
borders orange/yellow zone, although needle rests closer to white zone.

Thanks for any help.
Bob Jacobs
88 900T 215k
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