You appear to be a group that welcomes a challenge!
Here's an email I recently posted elsewhere, with no response. I trust some here may rise to the challenge:
I have travelled here many miles across the circuits of the interweb from the Alfa Romeo BB, optimistic the accumulated wisdom of Automotive Electrical & Sensor Forum members will assist me in my quest.
Series 3 Alfa Spiders, from the early to late 80's used two different Bosch computers for their 2L, DOHV, L-Jetronic injected engines. One computer handles fuel, injection duties and the second, ignition timing. The latter computer has the following inputs: TPS (1/0), flywheel position sensor, flywheel RPM sensor (2 sensors on the flywheel?, don't ask and finally, the reason I'm here, a Vacuum Sensor Device (VSD).
The VSD receives a vacuum signal from the intake manifold, and by means of a copper bellows (hey, I'm talkin' the 80's here ) moves a core within a coil to feed variable inductance to an oscillator in the Ignition Timing Computer. The computer massages the inputs and sends an appropriately timed (no pun intended) voltage to the ignition coil. Subsequently, the distributor functions simply as a four way, high voltage switch and does not factor into ignition timing in any way.
You're way ahead of me if you identified the weak link in this system to be the copper bellows, and tragically, all over this end of the galaxy, Alfa Spiders with failed VSD's have reverted to their base timing of 10degrees BDC, never again to provide improved fuel economy and performance .
A number of us on the Alfa Forum have considered, without success, a replacement A/D/A circuit for the VSD to no avail and are optimistic engineers (and techies :-) here may have some ideas.
Here are the electrical specifications we have measured, using my VSD: Coil inductance at Max Vacuum (about 20#, limit of core travel), 3.6 mH; at zero vacuum (WOT) 2.5 mH. Resistance of the coil is 50 ohms. As an aside, have also discovered removing the electrical connection between the VSD and Ignition Computer results in ignition timing at idle going, to use the technical term, "nuts", with the timing mark jumping all over the harmonic balancer and manifold vacuum a shaky 5#.
On behalf of the hundreds of unhappy Alfa owners, I beseech you all to give our problem some thought and rise to the challenge!
Thanks and best wishes.
Steve Waclo, EE, ret (knew T. Edison personally )
One other point, I have no way of knowing the characteristics of the vacuum/inductance curve of the VSD through it's range and presume linearity.
And one other, other point. Contrary to my usual practice, I did not search this Forum for previously posted 411 on this topic :-).