1979-1993 & 94 Conv [Subscribe to Daily Digest] |
 | [Main C900 Bulletin Board | BBFAQ |
Prev by Date | Next by Date | Post Followup ]
Member Login / Signup - Members see fewer ads. - Latest Member Gallery Photos
So, the APC pressure transducer... Posted by Justin VanAbrahams [Email]  (#32) [Profile/Gallery]
(more from Justin VanAbrahams) on Tue, 9 Dec 2014 19:07:36
Members do not see ads below this line. - Help Keep This Site Online - Signup
|
Over the last 5-10 years, I have found that virtually every APC failure I've experienced has been the result of either the solenoid (common forever) and the pressure transducer under the dash (common recently). The symptoms of the former is usually "stuck in base boost," whereas the symptoms of the latter are typically "stuck in low boost, but maybe not base boost." My SPG developed the latter - suddenly stuck at about 7psi instead of the expected 12psi. The diagnosis is always easy - hook up a Mityvac to the cabin-side vacuum system and put some pressure into it with the ignition on. In this case, the solenoid started chattering away at only 7psi - voila, correlation.
I have a small collection of Probably Bad pressure transducers collected over the years, so tonight I got bored/adventurous and hooked up each to the Mityvac and a multimeter. What I found is that all of them save two displayed the same symptoms - ~10ohm at atmosphere, 50ohm at 5psi, and then at some greater number a totally unstable reading flopping around all over the place. One of them had infinite resistance, one of them displayed lovely linear response - 50ohm at 5psi, 100ohm at 10psi, and 150ohm at 15psi. I'm planning on putting that one in the SPG later.
The one Very Bad part - the one with infinite resistance - I sawed open to see what was going on inside. I can't believe that in all these years I never did that, but whatever. Inside is exactly what you'd expect for '80s technology - a diaphragm that deflects a wiper across a resistor. The issue with this particular bad one is that one of the wires detached internally from its terminal. I'll post a picture later.
Now what I am wondering: Does anyone know what resistance is *supposed* to be for these things? Is 10ohm per psi correct? Secondly, anyone aware of a resistive pressure sensor that might take the place of the factory part? With patience, repair of the stock stuff could be done, but I feel like there has got to be something similar out there.
posted by 69.62.18...
, Tue, 9 Dec 2014 19:07:36 <-- Viewing This Message, Tue, 9 Dec 2014 23:03:58
, Mon, 15 Dec 2014 07:02:58
, Wed, 10 Dec 2014 07:10:46, Wed, 10 Dec 2014 10:41:25, Wed, 10 Dec 2014 12:26:27, Wed, 10 Dec 2014 10:04:15, Wed, 10 Dec 2014 10:34:39, Wed, 10 Dec 2014 11:42:26, Wed, 10 Dec 2014 13:05:17, Thu, 11 Dec 2014 06:49:36, Thu, 11 Dec 2014 11:06:36
No Site Registration is Required to Post - Site Membership is optional (Member Features List), but helps to keep the site online
for all Saabers. If the site helps you, please consider helping the site by becoming a member.
 |
 |
 |
 |
 |
