Vacuum Pressure Sensor
inside out

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Interesting!

Does it look like something that could be repaired? I thought I had a source for 'rebuilt' pressure sensors but they have never replied to my inquires.

Python Injection, Inc.

You can find them used from (EBay store, "rezdoc") De Noya trading post in Oklahoma.

Elio

ghnl: yes you can reapir it, visible crack can be soldered, then casing can be soldered as well, and the best part is, that as long as this sensor is not making anynboise, you dont really known that is broken, because your alfa can drive without it.
Elio: yess, and that is exacly the source where i`ve got my replacement, (just in case) before I`ve opened this one.

Maciej,

How did you open the can? Can you see the place where the copper is cracked? I can't make it out in the picture, but maybe that's because I don't know what to look for. This is a great picture set, but needs a little extra material to know how to use the info.

I am very interested, because I now have a whistling unit in my desk drawer as well as one in the '86 Spider. It lasted a year or so from my purchase from (drum roll....) de Noya. And yes, the mileage seems to have dropped with the unit bypassed (reduces spark advance and therefore cruising efficiency). I didn't expect the drop to be noticeable, but it seems to be.

Michael

Very cool photos. I was hoping cut open the failed unit from my car and post photos (someone had asked for that, but I forgot who), but I have yet to have the time. I ordered a used replacement from DeNoya, but it was defective right from the start. I sent it back, and Louie is sending me another one. What I find most interesting about the photos is that they reveal that I had been in error: I thought there were rubber (or something similar) membranes that would split and create the whistling noise. I had no idea that there was copper tubing in there. Perhaps failed units can be repaired.

Bypassing this unit definitely creates a noticeable difference in the car's performance, particularly at startup and idle (not nearly as smooth). Furthermore, I had to dial back the mixture (using the AFM flapper dial) a bit because the lack of spark advance resulted in a rich condition at mid-throttle.

i`ve cut it open with the dremel, then to put together i`ve soldered around, but as i figure it out later there is a more ways to put this together....
picture shows where crack is... and i think these parts are separable without damagin g them, but I didnt try... so im encouraging somebody that has broken sensor to try to open it, ))))
i`ve soldered that crack and id worked...

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I"d hoped to use a durable plastic tape like Kapton, with an adhesive backing, for sealing the copper against leaks. The copper seems to fatigue over the years, and it will probably crack all around its periphery. I can't tell how one would repair this item without replacing all of the side panel of the chamber. But maybe (as I think about it more) something that is forever rubbery would work? Something like contact cement? RTV? I'm not certain how durable those would be, but I believe the Kapton tape would be prety durable.

Michael

may be durable, but would seal properly?
now im thinking that your Idea with rubber cement is better than soldering

Why not just lock the movable part in the full advance position? Back off for detonation or run premium.

I realize that this thread is quite old but I would like to revisit this after doing a search for more info and not finding the answer.

I have taken the Vacuum sensor apart becasue it was leaking badly. It had a big crack just like the one in the picture but in a different place. I have cleaned and sealed it with blue RTV silicone and now the copper bellows holds a vacuum.

My question is this:

Does the complete housing have to hold a vacuum once assembled or is there a "controlled" leak built in. The reason I ask, is now that the housing is in 2 pieces, I can draw a vacuum on the electrical long thin portion (from the bellows end) and it will allow air to come in. Should I spend some time sealing this end up before reassembling the housing?

Jon

The outside of the bellows needs to be exposed to atmospheric pressure, that is thru the little black cap which has holes in it.

The inside of the bellows needs to hold a vacuum. If you suck on the port that connects to the intake Manifold and it leaks (does not hold a vacuum) then you have not sealed the bellow cracks.

Realise also that there need to be a movement in the bellows with vacuum. If there is too much silicone and the movement is inpeded, then the calibration is off...so is the spark advance.

TTFN Elio

And if you like picture (well, sketches):

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Thanks for the answers! The sketch I'm pretty sure solves my mystery. It must hold a vacuum thru port 5. I'm getting air leakage thru the plug area at the top. I will seal this and get it to make a vacuum, then reassemble the complete unit.

I used as little silicone as possible to make the seal/fix. It's got to be better than blocked off or leaking!

Yes better than nothing...however you have at best a temporary fix and the unit calibration (output curve to the ECU will be off.
Other MAP sensors (other than Bosch) are available.
Best regards, Elio