what voltage does the MAP sensor have to send to say boost levels are at 20psi?

 

5v i m pretty sure.....y do u ask?

 

5v is the power supply i need to know what the signal voltage back from the sensor is at 20ish PSI. im just making my own boost fooler since i get resistors for pocket lindt.

what does the computer assume for boost if the sensor is unplugged?

 

I may be wrong, but I think the computer goes into limp mode when I doesn't get signal from the MAP sensor.

You might check the Dodgeram.org site--I'm pretty sure Dave has the details on both the MAP and IAT sensors there in his tech pages.

Mike

 

Here are the voltages for the MAP sensor for an SO VP44 truck.

Pressure (gauge) / Voltage
0 / 0
12.5 / 1.44 to 1.56
25 / 2.44 to 2.56
37 / 3.44 to 3.56
50 / 4.44 to 4.56

To make a boost fooler you must clip the MAP voltage at a level that will not set a code and defuel. For an SO VP that voltage is slightly more than 2.25 volts. The circuit is best made by using resistors and diodes because it is important to track the MAP voltage up from zero to 2.25 without attenuating it. The ECM decides how much fuel to inject based on the MAP voltage. If the voltage is lower than normal the ECM will not fuel as hard.

If you have an HO VP44 the MAP voltage was changed to be zero volts at zero psi absolute. The MAP sensor has a different electrical connector and became a Manifold Absolute Pressure sensor. With this change, the pressure / voltage table above, subtract 15 psi from the pressure to get the Gauge reading and voltage. The Gauge reading is what you will see on your in cab boost gauge.

Unplugging the MAP sensor will make the ECM think the boost is too high.

 

so just a resistor from the supply to the signal will actually be less effective then leaving it plugged in at normal operation? i would just gain no code with the boost above 21 and no bottom end fueling with the computer thinking its at full boost?

 

Yes, that is exactly what will happen if just using a resistor divider.

I even tried an amplifier to make the ECM think the boost was higher than what the MAP was indicating but had it clipped at 2.25 volts to avoid defueling. The effect caused over-fueling at low RPM and not much increase in power but lots of smoke.

The MAP signal is well calibrated to get the most power for the air pressure and screwing around with it didn’t help me.

 

i put a resister on my truck when i was on injectors only, and i thought it worked well,

i unplugged the map connector, and put a resistor from the 5v to the signal, and i got more low end smoke, and on the high end it didnt defuel!, lowered 1 second on the 1/4

 

over-fueling at low RPM

There it is again.
The term over fueled.
don't you mean under aired?????!!!!!!!!

 

Over fueled = smoke. Under aired = smoke. Therefore over fueled = under aired. Just two sides of the same coin.

In all honesty, changing the MAP voltage to increase fueling was not effective for my butt dyno. On a real dyno it probably will add some HP. Using a resistor from +5 to the signal lead can cause some codes. The ECM will check the MAP voltage on engine start and expects to see a voltage that corresponds to 0 psi. If the resistor raises the voltage too high, it can go into “Limp” mode.