'84 Spider Vacuum Sensor "whistles" - Alfa Romeo Bulletin Board & Forums
 
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post #1 of 15 (permalink) Old 03-24-2008, 05:45 AM Thread Starter
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'84 Spider Vacuum Sensor "whistles"

The car has been running fine for a long while. I'm replacing the carpeting throughout the cockpit. Removed the passenger side panel to expose the Motronic device and the Vacuum Sensor. The vacuum hose was NOT connected to the sensor. When I started the engine, the vacuum hose "sucks" very well. When I connected it to the Vacuum Sensor, the sensor "whistles". If I hold my finger on the Sensor opening on the bottom with the hose connected the whistling stops. If I drive it whistles, except when I get to a hight RPM. I've driven it with the hose connected and with the hose disconnected, and cannot see any performance change.
What do you think has happened?
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Ray Kiszely'84 Spider Veloce
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post #2 of 15 (permalink) Old 03-24-2008, 06:06 AM
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There is a metal bellows inside the vacuum sensor. The whistle is because the bellows has split.

There is a thread here that shows a vacuum sensor disected (a search should find it). If anyone figures out to repair them please let us know. These units are expensive to buy new.

The major difference you'd likely notice with a functioning vs non-functioning vacuum sensor is in fuel mileage. The computer uses the info from the sensor to adjust (advance) the ignition timing under cruise conditions (light throttle/low load).

- - Eric
don't read this
~ 1984 Spider Veloce ~
- -~ 1981 GTV-6 ~
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post #3 of 15 (permalink) Old 03-24-2008, 06:12 AM
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The whistle is air being sucked into a crack in the internal bellows.

Without, the Manifold vacuum sensor, there is no advance of the ignition spark. If it is connected and leaks, the advance is not correct and will get worse. It affects combustion and performance.

The sensor is expensive, and used ones are either already fatigued to leak or have short life. I went through 2 that I bought on eBay, then bought a new one.

I have an extra one, as new, in a box. PM me if interested.

Best regards, Elio
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post #4 of 15 (permalink) Old 03-24-2008, 06:20 AM
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There is a sketch of the innards here: 86 Quad whistles

and the disected sensor here

- - Eric
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~ 1984 Spider Veloce ~
- -~ 1981 GTV-6 ~
Mebane, North Carolina


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post #5 of 15 (permalink) Old 03-24-2008, 10:46 AM
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I drove around for a season with this senson disconnected and no problems. I suppose my mileage was worse, but I didn't notice it since I'm seldom cruising on the highway. The cost of the sensor at retail takes a while to recoup on fuel economy. However, I did see that there is a VW part# where the same sensor can be had for quite a bit cheaper. I don't remember where I found it, but if you search the archives, I think you'll come across it.

Tim

Tim

Current: '78 spider with dual Webers and lots of smiles.
Former: '86 Spider that now lives a mere 30 miles away.
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post #6 of 15 (permalink) Old 03-24-2008, 10:51 AM
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Quote:
Originally Posted by RayKiszely View Post
If I drive it whistles, except when I get to a hight RPM.
Well you already found the answer to your troubles

[B]eb[/B]
85 Spider 71 GTV

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post #7 of 15 (permalink) Old 03-24-2008, 01:35 PM
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I have the same whistling, yes its the metal bellows gone bad. My mileage is 27MPG currently. I plan to search the BB and find how it was fixed (solution probably in links above). maybe I can get 30mpg - you know, these cars are (were) considered "thirsty" back in Italy.

Tony G. in NJ

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post #8 of 15 (permalink) Old 03-25-2008, 11:43 AM
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Leaky Sensor

I found the performance noticeably improved with a functional sensor, as mine was broken when I first got the car and when I got around to replacing it, the performance was much better.
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post #9 of 15 (permalink) Old 03-25-2008, 11:55 AM Thread Starter
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I'm getting one, to fix the whistle

Thanks for the info, I'm looking forward to improved performance. I'm buying the extra one that Elio in Canada has. I had an extra one myself from an '87 Quad that I sold to a fellow named Jim, you just don't know what to keep when you break up a car.

Ray Kiszely'84 Spider Veloce
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post #10 of 15 (permalink) Old 06-18-2019, 12:41 PM
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Hello
Unfortunately I lost my photo with pipe connected to vacuum sensor in my spider 1982.
If somebody have some information - diagram L-jettronic system no shows any.
There are only line without vacuum sensor.
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post #11 of 15 (permalink) Old 06-18-2019, 02:02 PM
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When I was in high school the one on my 83 Spider started whistling. I cut it open, put some RTV on the pin hole in the bellows, epoxied it back together, and it worked the few more years I owned the car.
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post #12 of 15 (permalink) Old 06-18-2019, 02:15 PM
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Interesting thread. Not sure about mine, no whistle but sure would like to confirm if it is working properly. Could you hook up a timing light and look for advance?
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post #13 of 15 (permalink) Old 06-18-2019, 02:18 PM
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Where would I find the info on this system on the CarDisc? Searching for stuff on that disc is time consuming!
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post #14 of 15 (permalink) Old 06-19-2019, 12:07 PM
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Curiosity got the best of me and I headed to the garage. I started the Alfa, noted rpm (950-1K there about, 1300 on tach. lol) pulled the hose on the plenum feeding the VSD and plugged it. No change. Even played with throttle a bit in both scenarios and could tell no difference, not that this is a conclusive test.... I will open up that panel some time when it is not 105 degrees outside to replace that section of vacuum hose and give it the suck test to see if it holds vacuum. I think that will confirm condition of the device. Do you think that is a proper test of its integrity?
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post #15 of 15 (permalink) Old 06-23-2019, 08:19 AM
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I guess there is not much interest in this thread.
This morning, I went out and hooked my Mity-vac to the VSD hose at the intake plenum. Would not hold vacuum. Opened panel where VSD and ign. Control is and found a golf tee stuck in the hose intended for the #5 port on VSD... I guess hose was leaking too! Anyway, I removed the VSD and ground the flange off to inspect. That went easy but could not figure out how to get the bellows out from there. Would someone please give me a source to buy a new one? I may still try to repair this one but would just like to bite the bullet and find one NOS. If no NOS available, any idea of a used one? Maybe Alfa Parts in the Bay Area? Thanks. Until then I just plugged it at the plenum. I think I found my irratic idle and low RPM hesitation..
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