Need MAP Voltages...

From across the Country.

In particular, I need a Sea Level Reading and as many other poinst between there and the 6,000' altitude I am at. I need to see if the Factory MAP Sensor is a linear device.

So, to gather the data, turn the ignition on and with the engine not running, record the voltage at the MAP Sensor. The voltage can be taken by back probing the connector. There are three connection points on the MAP Need the readings from the center wire to ground.

At Sea Level, the voltage should be in the neighborhood of 4.6VDc. More or less.

So I will need the Altitude where the reading is made and the voltage reading. You should be able to Google the altitude for your City.

My plan is to use a (Spare, doesn't everyone have a spare Sensor?) Factory MAP and a Comparator Circuit to trigger a relay to shift my F/IC from "low" altitude to "high" altitude settings. Yes, I already know it is a complication so don't bother to tell me. I am retired, have tons of time on my hands and would like better resolution in the F/IC which, as of this moment, has a tune in it to go from Sea Level to 14,000'. I have all of the components, just need the readings to set the circuit trip point.

Thanks in advance.

I think I have that info at home, but if you mention using a relay, so that tells me it is a single point control system, so why wouldn't you simply go to your selected altitude and then set it?

3.95 at 5,300 feet.

o-gauge-steamer said:

I need to see if the Factory MAP Sensor is a linear device.

Click to expand...

The answer is yes. The MAP output voltage is indeed directly proportional to the manifold absolute pressure. This link provides some useful info.:

http://www.fastfieros.com/tech/map_sensors_and_how_they_work.htm

old_man said:

I think I have that info at home, but if you mention using a relay, so that tells me it is a single point control system, so why wouldn't you simply go to your selected altitude and then set it?

Click to expand...

Tom,
I do not want to drive all the way down under La Junta...

Just both lazy and too cheap to spend the bucks on fuel.... Time I have, money not so much. Kids and thier University expenses.

Going to build the Comparator but I sort of need the number to build it to compare to... The value I get will determine the components needed to build the circuit. It's a Chicken and egg thing I suppose.

Cruiser, thanks for the numbers!

Dr. Dyno. Just because something is alledged to be linear does not mean that it is. I am a Retired Engineer and I do not now nor have I ever accepted unproved data. It is my personal Deamon... Plus, the chart in the link had approximate values and I need what the Sensor in a Heep reports. I checked my Jeep, a spare GM 1 bar and a 2 bar MAP that I have kicking around and they all reported different values within 5 minutes of each other. Different Sensors give different results. Interesting, yes?

Plus, I need the voltage at 4,000' altitude or close to it. I have a good chart on PSIa for the F/IC to be set by. Just need numbers.

What sensor are you using an absolute or differential? The early sensors sampled atmospheric, recorded it, and used that as a base. As altitude changed, they ran like crap until the car was shut off and restarted from the updated base recorded atmospheric. New sensors constantly adjust for atmospheric. GM and Mopar sensors have different curves as well. What is the OE p/n of your MAP? I have manufacturer's data for most MAP

I have a few PNs:
84-96: 33000153
2000: 56029405
2004: 56044545AA

I believe the 84-96 was just a GM map sensor as it is also sold under GM and Ford part numbers.

Talyn said:

I have a few PNs:
84-96: 33000153
2000: 56029405
2004: 56044545AA

I believe the 84-96 was just a GM map sensor as it is also sold under GM and Ford part numbers.

Click to expand...

Correct, and it mounted on the firewall. Later models had the MAP sensor mounted on the intake somewhere.

It was mounted directly to the throttle body.

o-gauge-steamer said:

Different Sensors give different results. Interesting, yes?

Click to expand...

Indeed and that's the problem with asking someone else to report the MAP voltage for his Jeep at his elevation. His sensor isn't the same as yours so the results will indeed be different, but they should be close enough for you to work with.
The relationship between MAP voltage and manifold pressure IS linear except at the two extremes of the graph. The MAP sensor works on the same principle for most vehicles with a 0-5v output range. The only difference between a 2-bar sensor and a 1-bar sensor is that the 2-bar sensor will output near 5v at 29psi instead of 14.5psi, and the 2-bar sensor will output exactly 1/2 the voltage at any given pressure as the 1-bar sensor.

If the MAP sensor is stand alone to measure gauge pressure, an actual baro sensor such as GM 16006833, 16038591,16022790 / SMP AS11 will be more accurate.

More Specific...96+ Map Sensors as my Heep is a 98!

@ 40' above sea level 4.65 volts out with 4.95 volts measured at the Vcc term

Thanks Ordnance, I have put the data into the spreadsheet. Your reading is right where the FSM would lead me to believe it should be for sea level. So, for that matter, is the 4.95VDc Vcc reading. Looks like you have a keeper on your hands!