ChrisUlrich

What is the purpose of a MAP Sensor? What is the different between a 3 bar or 4 bar MAP Sensor?

What would happen if you try to tune a car that requires a 4 bar MAP but you only have a 3 bar?

VinceTrifecta

MAP = Manifold Absolute Pressure. This sensor is one way the engine determines how much load is on the engine. Stock MAP sensors on normally aspirated engines are 1 bar, which means they can measure up to the atmospheric pressure. Anything higher then 1 bar means the sensor can measure manifold pressures that are higher then the atmospheric pressure (e.g. forced induction).

If the PCM's assumption about the MAP sensor doesn't match the MAP sensor, the PCM will incorrectly calculate engine load which can result in fueling and spark advance miscalculations.

ChrisUlrich

So at what point would you need to get a different MAP sensor on a car like a ???? or something?

98turbls1

iTrader: (17)

The metric measurement of "Bar" is actually 14.7psi per each full value... For example:

1 Bar= 14.7psi but it's atmospheric pressure which is there all of the time so people refer to this as 0.

2 Bar= 14.7psi of actual boost. If you're going to go higher than this you're going to have to go to a bigger Map sensor.

3 Bar= 29psi give or take or almost 3 times the weight of gravity. Now some people ask why don't they just go straight to 3 Bar. The reason you don't want to is because of resolution. If you're only going to go to 12 psi and that's it then why loose resolution to a larger MAP for the sake of MAYBE upgrading down the road. Basically use the smallest one that you can for your application so that you retain as much resolution that you can. In an LSX PCM you're only able to go to a 3 Bar in 99+ PCM and only to 2 Bar in 97-98 PCMs. (With HP tuners, I don't believe that EFI Live offers a SD tune option for 97-98 PCMs but I don't follow them that much)

I hope this clears it up a little bit better.

VinceTrifecta

Basically, you need a different MAP sensor if you are going to run forced induction (turbo or supercharger), and you can tune the PCM to work with a different MAP sensor. There are other fueling solutions for forced induction that do not require a special MAP sensor, however.

ChrisUlrich

Yes... thank you!

But now what happens if you try to tune a car with a bigger turbo then the MAP sensor is meant to handle? Say a 2 bar running 20-22 psi?

98turbls1

iTrader: (17)

Then it's going to act like a car that is tuned with a MAF that is maxed out.... It's not going to be able to sense the extra boost... Better make sure that it's extra rich there because it's going to have no way to calculate that boost...