New VSD installed - Alfa Romeo Bulletin Board & Forums
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post #1 of 12 (permalink) Old 07-01-2019, 03:55 PM Thread Starter
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New VSD installed

I received my new VSD today in the mail. I installed it, pulled the plug off the plenum, put the new vacuum hoses on it and fired her up.
The idle is much smoother, doesn't "hunt" for the first couple of seconds like it had previously. Off idle throttle seems smoother but haven't driven yet, I will get around to that this evening. Thanks to whoever revived that old post and led me to that device that I had no idea it was there!
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post #2 of 12 (permalink) Old 07-01-2019, 04:36 PM
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What is a VSD?

Bill

1991 S4 Spider "Gabriela", 2017 VW Golf R, 2018 VW GTI,

Previous obsessions; 2006 Mustang GT, 2006 BMW Z4M, 5 other Bimmers, Capri V6, Renault 5, Lotus Cortina, Sunbeam Alpine, Ducati Diana Mk 3, Norton Commando
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post #3 of 12 (permalink) Old 07-01-2019, 04:50 PM Thread Starter
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It's the vacuum sensor device on an L-jet that controls timing at idle and low load scenarios. I knew that these systems were vacuum sensitive but had no idea this device was hidden in the quarter panel behind the passenger seat. A member revived an old thread that talked about a "whistling" coming from the parcel area. Mine was plugged with a golf tee.....
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post #4 of 12 (permalink) Old 07-02-2019, 06:28 AM
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I received my new VSD today in the mail.
Where did you get a new VSD?

Gary
87 Spider Veloce
Spring Hill, TN

As of 9/29/19: NEXT: Fix foot-well lights, gas lid.
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post #5 of 12 (permalink) Old 07-02-2019, 07:19 AM
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I was under the impression that the device on the wall behind the passenger seat in S3's was more of an "altitude" or air pressure sensor, which had little to do with the intake vacuum pressure, and new or replacement units were no longer available.

Edward
'88 Quad - "Claudia"
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post #6 of 12 (permalink) Old 07-02-2019, 08:36 AM Thread Starter
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Certainly air pressure changes with altitude which would affect the amount of advance the VSD's "baseline" is, but the bellows ( which sends the variable signal to the ignition module to control timing) is controlled by vacuum pressure from the plenum. Ordered it from Alfaholics as a used item but it truly looks pristine. It is new to me for sure. If you have disabled yours I would consider finding a "new" one. Acceleration is noticeably smoother, idle is much better too. I am waiting the see the fuel mileage comparison.
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post #7 of 12 (permalink) Old 07-02-2019, 04:19 PM
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Originally Posted by SkiBum View Post
Certainly air pressure changes with altitude which would affect the amount of advance the VSD's "baseline" is, but the bellows ( which sends the variable signal to the ignition module to control timing) is controlled by vacuum pressure from the plenum. Ordered it from Alfaholics as a used item but it truly looks pristine. It is new to me for sure. If you have disabled yours I would consider finding a "new" one. Acceleration is noticeably smoother, idle is much better too. I am waiting the see the fuel mileage comparison.
Good on you!

If your idle improved with a new VSD, the original must have been leaking seriously. Cracks usually present as a quite small leak and if yours progressed to an idle issue, well...

Several years ago I worked with a control engineer who designed and tested a mostly electronic VSD. I used a Chrysler corporation MAP unit for a vacuum sensor and sent him ignition advance data which I laboriously documented with a vacuum gauge. He used those #’s to design a device that converted MAP output to a signal the Ignition CPU could work with. Still operates!

There are posts searchable with my user name.

I did a before and after mpg test and went from about 26 (+/-) to 32 on a flat, 75 mile (+/-) round trip, but economics did not pencil out for production.

Now, I am the only owner of an ‘87 Quad on this side of the Galaxy with a semi-electronic VSD!

Contrary to your results (placebo effect? ) I found no observable difference in acceleration. That was seat-of-the-pants of course, since I was laughed out of all local drag strips .

Also, there is a separate barometric sensor under the back shelf to adjust ignition (I think) and injection parameters.

On a related, performance topic, and at the risk of highjacking the thread, I still await Dyno results for w/wo our pioneering variable valve timing device (VVT). I believe it only actuated when a switch on the throttle mechanism closes at WOT, but no matter how carefully I sneak up on it, I’ve never felt any performance difference. I’ve confirmed clicks at VVT and throttle switch, and energizing it directly with a jumper at idle causes roughness.

My understanding is VVT was incorporated into L-Jet to provide a stable idle with improved WOT performance.

Best

Steve Waclo Carson City, NV; '87 Spider QV, ES Champion, 2018 Reno SCCA (125k);'93 Honda Nighthawk 750 (105k);'03 GMC Sierra SLE 2500HD Turbo Diesel (155k);'08 Altima Coupe 3.5SE, 6sp (125k)

Last edited by Stevew; 07-02-2019 at 04:23 PM. Reason: Getting old.
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post #8 of 12 (permalink) Old 07-02-2019, 04:27 PM Thread Starter
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Quote:
Originally Posted by Stevew View Post
Quote:
Originally Posted by SkiBum View Post
Certainly air pressure changes with altitude which would affect the amount of advance the VSD's "baseline" is, but the bellows ( which sends the variable signal to the ignition module to control timing) is controlled by vacuum pressure from the plenum. Ordered it from Alfaholics as a used item but it truly looks pristine. It is new to me for sure. If you have disabled yours I would consider finding a "new" one. Acceleration is noticeably smoother, idle is much better too. I am waiting the see the fuel mileage comparison.
Good on you!

If your idle improved with a new VSD, the original must have been leaking seriously. Cracks usually present as a quite small leak and if your’s progressed to an idle issue, well...

Several years ago I worked with a control engineer who designed and tested a mostly electronic VSD. I used a Chrysler corporation MAP unit for a vacuum sensor and sent him ignition advance data which I laboriously documented with a vacuum gauge. He used those #’s to design a device that converted MAP output to a signal the Ignition CPU could work with. Still operates!

There are posts searchable with my user name.

I did a before and after mpg test and went from about 26 (+/-) to 32 on a flat, 75 mile (+/-) round trip, but economics did not pencil out for production.

Now, I am the only owner of an ‘87 Quad on this side of the Galaxy with a semi-electronic VSD!

Contrary to your results (placebo effect? <img src="http://www.alfabb.com/bb/forums/images/AlfaBB_2015/smilies/tango_face_grin.png" border="0" alt="" title="Big Grin" class="inlineimg" />) I found no observable difference in acceleration. That was seat-of-the-pants of course, since I was laughed out of all local drag strips &#x1f630;.

On a related, performance topic, and at the risk of highjacking the thread, I still await Dyno results for w/wo our pioneering variable valve timing device (VVT). I believe it only actuated when a switch on the throttle mechanism closes at WOT, but no matter how carefully I sneak up on it, I’ve never felt any performance difference. I’ve confirmed clicks at VVT and throttle switch, and energizing it directly with a jumper at idle causes roughness.

My understanding is VVT was incorporated into L-Jet to provide a stable idle with improved WOT performance.

Best
Acceleration smoother, not faster. Kudos on the electronic VSD. Why don't you post the research and the build? I would be interested in your findings...
FYI, I don't get suckered into a "placebo effect". Much too analytical for such nonsense.
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post #9 of 12 (permalink) Old 07-02-2019, 04:38 PM
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Having read the above...confirms my belief carbs or mechanical fuel injection..I am an analog guy in a digital world..
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The older I get.. the faster I was....
Tom
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post #10 of 12 (permalink) Old 07-02-2019, 04:42 PM Thread Starter
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Having read the above...confirms my belief carbs or mechanical fuel injection..I am an analog guy in a digital world..
Believe me! If I had the option I would surely convert to carbs and ditch the computers but living in CA that is not an option with our ridiculous smog laws.
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post #11 of 12 (permalink) Old 07-20-2019, 05:35 AM Thread Starter
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Update since operating VSD install. Around town I notice a difference in idle and gradual acceleration, just smoother. Gas mileage has certainly improved but the biggest difference is high rpm cruising. Now over 4K rpm the car feels like it "wants"'to be there instead of "can"'be there, if that makes sense to you.
I could have driven forever not realizing something was missing until I stumbled on that old thread. It is certainly worth the time to make sure it is working properly. FYI, it had passed CA smog twice without it just fine....
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post #12 of 12 (permalink) Old 07-20-2019, 10:01 AM
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Where did you get a new VSD?
Was there an answer to this question in this thread that I missed?

jeff

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