MAP not holding a vac? Screw stripped? Fix it!

[Tomguy]

Well, I did it... I wanted to make sure I didn't have any problems, so I waited a few days before posting this advice, lest someone follow it and ruin their MAP sensor completely!

My MAP sensor screw was completely stripped (I couldn't turn it one tiny bit). Well, it also leaked vac, so, I decided to take it apart.

The diaphraghms inside are actually metal, not rubber! So they do not dry-rot as I read previously. The reason why it leaks is that there is a rubber seal going around the two halves (where the 4 slotted screws are). I cleaned and reseated my seal (once finished with the rest) and it held vacuum perfectly fine.

To fix the stripped-screw issue, I took a T-27 torx bit and hammered it into the offending screw, then pulled it out. Now, I use this bit (inside a screwdriver, naturally) to adjust the MAP. I had the halves apart and the top half lying flat on the floor when I did this. I removed the bit to make sure my new means of adjusting it wasn't lost (I COULD have left it in there - I checked mine and it did still allow air to flow through it. But if you do this, make sure air can move around it - this is where the MAP recieves the outside atmospheric pressure from, for readings, closing this off will screw up your MAP!).

I also cleaned the inside of it out with rubbing alcohol - I rinsed it a few times, then I let it sit upside-down overnight. In the AM I put it upright for another hour then re-assembled it.

I am glad to say that I can once again adjust the fuel-mixture in my car! And having a leaky MAP sensor is a bad thing - the seal is right by the diaphraghms!

[WANT '71 280SEL]

Did the vacuum leak affect the car's running?
Thanks
David

[Tomguy]

Unsure - If I had a CO meter and I didn't adjust the screw at all, I would be able to say yes with near certianty, though.

[psfred]

MAP sensor is an anaeroid barometer that moves a slug in an induction coil. About the only thing that can go wrong with it is to leak vac or have an open coil.

Probably what kills most of them is metal fatigue and cracks in the anaeroid bellows so that they stop expanding and contracting with vac changes.

If it works better after fixing the gasket, hurrah! Much better than buying a new one.

Peter

[Tomguy]

Originally posted by psfred
If it works better after fixing the gasket, hurrah! Much better than buying a new one.

Peter

Indeed. I wish I could buy a new gasket though, I'm paranoid about it leaking now!

[tosbt]

Darn, I've been waiting for two days just to adjust mine. Look how much trouble you can get in over a little screw!