Okay I went to go order a new baro sensor today and a map sensor at least that is what I though it was called, but they said it was a manifole diff pressure sensor, is that what I have or is it a map sensor or is it a vac sensor? I am talking about the one on the firewall on the drivers side, does this one get vac? the car is a 86 lg4, and does the baro sensor have some kind of filter that goes on the nipple?

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BZ,

The Barometric Pressure Sensor detects just that - atmosheric pressure (density altitude, to be more precise). Most of them were equipped with a small cube of foam stuck to the vent fitting, but these didn't often last more than a few years without deteriorating or falling off. This "filter" isn't necessary for the sensor, but could possibly keep contaminants out of the pressure chamber (maybe). I'm guessing the factory installed them more so that the line inspectors didn't get confused, thinking a vacuum hose should be attached there.

The Manifold Absolute Pressure (MAP) sensor senses just that - absolute pressure in the manifold. A "perfect" vacuum is the same as 0 PSI Absolute (PSIA), while we more frequently measure pressure in PSIG (gauge pressure above one atmosphere). In absolute terms, atmospheric pressure (0 PSIG) is equal to 14.7 PSIA. Conversely, vacuum of 20" Hg is roughly the equivalent of 4 PSIA. GM used the absolute pressure scale so that the sensor could be used to determine manifold pressure/vacuum and the programming could be done with one scale, instead of having to factor vaccum in inches of mercury and pressure in PSIG. The ECMs are not THAT complex, after all.

Both sensors are very similar in appearance, since they have a nearly identical function. The major difference is that the outputs are scaled differently. The MAP sensor should have a hose connecting it to the intake manifold, while the Baro sensor has no hose connections. If you are in doubt about which is which, consult the vacuum hose routing decal under the hood.

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Later,
Vader
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"No matter how hard you try you can't stop us now"
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Oh wise vader..., i'm gonna have to send you a manual on CCCS cars one of these days, i think this is at least the second time you've been giving EFI ecm/sensor advice to someone with a carb. They have their own idiosynchrasies(sp?
Anyhow, unlike EFI cars which use a MAP sensor, CCCS uses a vacuum sensor (aka VAC, aka differential pressure sensor) which sends the opposite of a MAP signal. High voltage for high vacuum, low voltage for low vacuum. It is in fact located in the driver's side firewall, and should undeed have a vacuum line, which is connected to the carb on the little nipple coming off the back of the throttle body.
The BARO sensor is a MAP sensor with no vacuum line attached, and CCCS uses it as well.
...ed

edit...i'm still ROFLMAO...i see the common theme in your posts black, and i know what you're trying to solve...hehehe, makes me all warm and fuzzy to know 6 months later you're still trying...hehehe

[This message has been edited by Ed Maher (edited December 27, 2000).]

 

I will solve it one day I will I will I know I will.( I HOPE )

 

Ed,

If you have a "spare" I'm always looking for good reference material. I keep forgetting that there are a lot of carbed engines in the ThirdGen ranks. I haven't had a serious bout with the E4ME and E4MC carbs and their systems since about 1992, and would prefer to keep it that way.

Still, correct information is crucial, so thanks for the correction. We "old farts" need a kick in the pants once in a while between hits of Geritol to keep the symptoms of Alzheimer's in check. Still, I WAS trying really hard to forget the CC carbs.

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Later,
Vader
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"No matter how hard you try you can't stop us now"
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