Barometer reading??

[AudioFan]

Where does the PCM / Scan gauge reads the barometer?

I'm having some issues with my car, and noticed that the barometer stays at 10.7 when If I'm not mistaken it used to be at 14.7 (I'm at sea level)

Just trying to figure if some sensor are bad or what!

My 3 bar map, seems to be bad, while the car is off it reads -6, put the stock one, and reads 0.

Thanks for your reply

[moreause]

the barometric reading is from the tip

hum what do you have for pcm...stock one should not display zero
if your suppose to have the 3 bar map and tip

[AudioFan]

I have stage 3 pcm

I used to be stage 2 (3 bar map and tip) got the stage 3 upgrade, and car has not run good since installed

Shouldn´t be zero? I mean key in ON position, motor is off. I guess there is not supossed to be vacumm if the car is off

[moreause]

you said you put the stock sensor in (so i presume it is a 2.25 bar)
thevalue it gives at zero is not the same as a 3 bar so the pcm will not see
the correct value


and yes your suppose to see around zero boost pressure when the engine is off

[nutz]

you might be confusing psia and psig
psig=0 +/- engine variables
psia=barometer reading +/- engine variables

if its humid out the barometer will fall

[moreause]

yes the barometer can move but i don't think it will go to 10.7

and the pressure when the engine is off should be around zero
the gage use the atmospherique pressure to move the zero value
so the gage show psig value

[forcefedjunkie]

Quote: Originally Posted by moreause

yes the barometer can move but i don't think it will go to 10.7

and the pressure when the engine is off should be around zero
the gage use the atmospherique pressure to move the zero value
so the gage show psig value

what I do know (at least I'm pretty sure about this) is that the PCM takes a snapshot of the barometric pressure when the car is first started. This is what you will see as the barometric pressure parameter until the next time the car is started. We use this value to convert the absolute pressure reading from the MAP sensor to a gauge pressure reading, such as you are used to seeing with the stock boost gauge.

I cannot tell you what affects a 3 bar MAP will have on the barometric pressure reading, our car uses the stock MAP and this really hasn't been discussed here so I have no first hand knowledge. Hopefully others with greater knowledge will continue to post their findings.

Todd

[AudioFan]

I found the problem

The Stage 3 PCM that I received was damaged, because I installed my stage 2 PCM again, and all the readings went back to normal, barometer at 14.7, maniflod at zero when engine is OFF, speedometer is working again, fuel gauge is working, etc

Got rid of the codes that I had, battery light, and car is running good again, before it would not boost over 8 psi.

Thanks for your help

[SkullingAxe]

To answer the question about the barro reading...

The PCM takes a barro reading at key on and periodically through cruising. That's why there is a solenoid on the tip vacuum feed line. The solenoid bypasses the feed line and lets the tip sensor see ambient pressures. Then it goes back to reading from the feed line.

The only time it does not take a snap shot is when you are in boost. It runs off the previous reading until your out again. It does this so that when your driving on like a road trip you don't have to shut the car off at higher elevation and let the car take a reading.

And the barro reading is VERY important for the calculation of the fuel curve. Being off a few points will throw the fuel trims out of whack. Thats why when ever you get a 3bar map ALWAYS get the 3 bar tip as well.

On a non-boosted Chrysler the map sensor does this, and it takes a barro reading at key on and WOT.

Bryan