Third Generation F-Body Message Boards

Map Sensor review

Since I am going from Carb to Speed Density a whole ‘new’ technology I have to become familiar with. One of the key sensors in a traditional speed density setup is Manifold Absolute Pressure (MAP) sensor. MAP sensor technical information has been hard to come by. For example, what voltage one should expect at the terminal B depending on manifold vacuum.

In my conversion – I have no idea what cam is used with my 350. It appears to be a very mild RV grind. So, before putting the complete TBI system on top of this black box it would be nice to know what to expect.

I pulled couple of typical 1-Bar MAP sensors from J-Yards. These are GM 460 series MAP sensors with green inserts. I have tested both of them with my vacuum pump by varying inlet vacuum levels while recoding voltage output. Supply voltage was set at +5.0 Vdc as required by GM ECMs

Sensor #1 460-9004
Measured Data
In HG Vac Vmap <9004> kPa
0 ............ 4.83 ........... 100.0
6 ............ 3.83 ............ 79.7
7 ............ 3.61 ............ 76.3
10 .......... 3.06 ............ 66.1
12 ........... 2.719 .......... 59.4
13.5 .........2.42 ........... 54.3
19 ............1.31 ............ 35.7
23 ............0.65 ............ 22.1
25 ............0.268 ...........15.3
26 ............0.074 ...........12.0

Sensor #2 460-6294
Measured Data
In HG Vac Vmap <6294> kPa
0 ............ 4.908 ............100.0
2 ............ 4.56 ............ 93.2
5 ............ 4.09 ............ 83.1
7 ............ 3.698 ............76.3
9.5 ......... 3.25 ............ 67.8
13.5 ....... 2.46 ............ 54.3
16.5 ....... 1.89 ............ 44.1
18.5 ....... 1.53 ............ 37.4
20.5 ....... 1.08 ............ 30.6
22.5 ....... 0.696 ........... 23.8
25 .......... 0.30 ............ 15.3

Putting above raw data into a spreadsheet and surprisingly the two sensors correlate very nicely! MAP output voltage is a linear function (y=mx + b) of the vacuum at the input port:

Sensor #1 <460-9004>
Vmap= 0.054669721*Pressure (kpa) - 0.570241761

Sensor #2 <460-6294>
Vmap= 0.055432958*Pressure (kpa) - 0.566709374
Which can be plotted:

//RF