Alfa Romeo needs Vacuum Sensor Device

[stevewaclo]

Situation summary

Hello everyone!

Catching up on emails and before I am the cause of folks going off the rez, here's a refresher. Be sure to look at post 13 for the drawing of VSD internals:

https://www.alfabb.com/bb/forums/spider-1966-up/35224-reposting-missing-pictures.html

KISS asked for total coil deflection days ago, and I've got the 411 somewhere. Will discover secret hiding place soon.

Something else has occured to me. Look closely at the drawing on post 13 and you will notice the bellows is (are?) encapsulated in a sealed container, and contrary to what I would consider to be customary practice, vacuum from the intake manifold is applied to the exterior of the bellows. Correct me if I'm wrong, but I believe this means at max vacuum (closed throttle) the bellows will be fully extended, pushing the coil core to its upper stop.

Several have suggested using an off-the-shelf vacuum advance device as an alternative actuator, but again, unless my thinking is reversed, a conventional device will pull it's actuator arm at max vacuum.

Of course, if I stay in the mechanical realm, wind my own coil and attach an actuator, I could work the mechanism from the opposite end. I need to review notes from KISS, but despair winding my own coil without benefit of instrumentation to read mH values.

I've been quite scattered in my approach(es) to date (apologies) but although I would prefer mechanical modifications to the existing VSD, since mounting, coil value, connectors, et al exist, I'd still be stuck with analog.

Ultimate resolution lies in an electronic solution.

Best wishes

 

[alec_t]

Several have suggested using an off-the-shelf vacuum advance device as an alternative actuator, but again, unless my thinking is reversed, a conventional device will pull it's actuator arm at max vacuum.

If the movement is in the wrong direction you can reverse it with a simple pivoted arm. Appropriate positioning of the pivot point relative to the arm ends would also enable you to scale the movement amount to suit your needs.

 

[ronv]

I think you might be able to drill a hole in the opposite side of a standard vacuum advance and port the input to atmosphere. Might work if the size is right. You would have to put your slug on the end to make the sparks happy.

 

[Shawn Williams]

Hello stevewaclo,
I just bought an 86 spider veloce. Love it, but the vacuum sensor is kaput. I've read through your posts and I am curious if you found a solution.
I am an automotive EE, so I should be able to figure something out. But let's see....

 

[stevewaclo]

Hello again, everyone!

Seems like many months (wait a minute, it has been many months!) since I made time to check in with folks here who generously shared their knowledge and experience on the subject of automotive sensors and controls. The previous post, by new member (and new Alfa owner) Shawn Williams reminded me of my negligence. Shawn and I talked at length this afternoon (truth be told, Shawn did a lot of listening and I ran my mouth.)

To refresh memories, this post began with my request for assistance from the collective wisdom of the group in designing a replacement for the failure-prone electro-mechanical Vacuum Sensor Device (VSD) in Series 3 Alfa Romeos. The VSD, as you may recall, sends a signal to the Bosch L-Jetronic Ignition Electronic Control Unit (IECU) where, based upon engine load, additional timing advance is generated.

While ETO member K.I.S.S contributed a considerable amount of time and effort to the project (thanks Ron!) my lack of follow-through and fading enthusiasm ultimately closed that avenue.

So here's where things stand.

In the spring of 2013, Bob, a retired control engineer I met on another technical site, became involved in the project and, after digging into the Bosch IECU I sent him, extracted long-forgotten secrets buried deeply within the electronics. Bob learned the variable inductance of the VSD is connected to a variable oscillator in the IECU which subsequently results in modification of the engine's timing advance. Through further wizardry (and an engineering degree and decades of experience) Bob designed and built a prototype device, which I have cleverly named BD-1.0. Without an Alfa in his garage (Bob doesn't know how fortunate he is in that regard ) to test his device, he could only assure me that the IECU oscillator responded to BD-1.0 very nearly the way it responded to a know operational VSD.

Bob's design is currently in my hands and after I install a new fuel pump in my Alfa, a few tests should confirm that his design is a success!

Lesson learned (one of many). Do not assign projects to retired guys with grandkids and actual lives. All seriousness aside, the major foot-dragging was on my end and sincere thanks to Bob for his dedication and long hours.

Film at 11.

Bob's elegant work, and yes that's an analog, off-the-shelf MAP sensor. The main connector even matches OEM!

 

[Shadetree Fitz]

Stevewaclo,
Been following this string, wondering how you made out with MAP sensor that Bob made. Did it work? I have the same issue with my '85' Spider.

 

[joat]

seems to be a lot of extra effort that's not needed ... it's a simple vac advance unit with coil attached ( that converts physical movement to electronic signal )

delete the bellows and use a distributor vac advance unit from a regular distributor ... modify it to attach to your present signal device canister ...

a rubber diaphragm and rod out the back ... attach to the E that slides in and out of the coil ... and you have a working unit again

GM makes an adjustable ( max limit ) vac advance ....