MAP sensor voltage readings
- Thread starter sy2756
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MR_MNZTR_SY
New member
i did this a month or 2 ago and am not sure if i am remembering this correctly but it was confusing. you have the 3.5-5.5 as a referance and then at certain altitudes (or boost pressures) you subtract a certain amount of volts from that 3.5-5.5 and that is what your reading should be. man, that was probably way confusing. ill dig through the info i have and see if i still have it if no one else can answer this
Thanks for the reply. I live in Burlington, VT. The elevations is below 1000 ft so with the engine not running and the key to the run position chart c-1d sugguests that I should read between 3.8 and 5.5V. So I replaced the sensor as per the chart, I get the same 2.38 volts as with the original one. If I disconnect the sensor and repleat the test the voltage drops to .48 and if you jumper pins b and c the voltage reads 4.8.
Lynn D. Brown
New member
MAP Voltage
MAP Voltage
So, what does the MAP reading mean w the engine off ? Since the engine & Turbo aren't creating any Vacuum/Pressure, I guess it is measuring Atmospheric pressure ?
MAP Voltage
So, what does the MAP reading mean w the engine off ? Since the engine & Turbo aren't creating any Vacuum/Pressure, I guess it is measuring Atmospheric pressure ?
MR_MNZTR_SY
New member
werd 8)
when the engine is not running the map sensor acts as a baro sensor to give the ecm a sort of baseline reading of atmospheric pressure.
...and i cannot find the instructions on how to test the sensor so i cannot offer any new info. sorry bro :-?
when the engine is not running the map sensor acts as a baro sensor to give the ecm a sort of baseline reading of atmospheric pressure.
...and i cannot find the instructions on how to test the sensor so i cannot offer any new info. sorry bro :-?
Lynn D. Brown
New member
MAP Sensor
MAP Sensor
If U R trying to check the baseline calibration reading of the MAP - i.e. compare it to Atm P, I'm guessing U would compare it to barometric pressure. Wouldn't that be available at your local weather station ? - or if U have your own barometer ?
Just a guess - really don't know squat.
MAP Sensor
If U R trying to check the baseline calibration reading of the MAP - i.e. compare it to Atm P, I'm guessing U would compare it to barometric pressure. Wouldn't that be available at your local weather station ? - or if U have your own barometer ?
Just a guess - really don't know squat.
MR_MNZTR_SY
New member
well, you would need a scan tool of some sort to read what the truck is seeing for baro pressure. then i guess you could compare the 2 but i dont think hes got that sooooo time to grab that meter and see what the sensor sees. ALSO he could haave a situation like i have, where the map sensor seems to be functioning properly but the 'puter still reads it wrong
ECM supplies 5v to the MAP sensor, which in 2 bar config reads (roughly) from 20" vac to 15psi boost. (You do the "vac to kPa math, I'm an oldie that likes vacuum readings). Key on, not running, you'll read about 1/2 full scale of 5v - halfway between high vacuum & max boost (which is atmo), so 2.5v is about right. Low kPa = low pressure & converse. Measured this on the bench many times getting a cal for my software, so its right. You can nitpick what elevation you're at, but won't change much. The ECM's ADC converter reads this voltage in a scale of zero to 255, so aprox 0.02v per step. Atmo =~ 2.5v =~ 100kPa.
Measure the MAP voltage as you suck & blow into it - volts will decrease w/ sucking, increase w/ pressure.
Measure the MAP voltage as you suck & blow into it - volts will decrease w/ sucking, increase w/ pressure.
turbodog
Donating Member
from the SyTy.org archives:
william conti wrote:
> Hi group,
> I would like to know if someone could get me a map sensor voltage reading
> with the key on and the engine off for a stock sensor. Thanks in advance,
The exact voltage will vary with ECM reference voltage and barometric
pressure.
Usually they are about 2.28 volts, key on, engine off if the ECM ref is
close
to 5 volts, and you are not too far above sea level.
A *ONE* bar MAP sensor will read about 4.5 or so volts under the same
conditions.
Scot Sealander
In retrospect, Scot was (is?) pretty darn savvy on our engine control systems. I'd take his word on it...
william conti wrote:
> Hi group,
> I would like to know if someone could get me a map sensor voltage reading
> with the key on and the engine off for a stock sensor. Thanks in advance,
The exact voltage will vary with ECM reference voltage and barometric
pressure.
Usually they are about 2.28 volts, key on, engine off if the ECM ref is
close
to 5 volts, and you are not too far above sea level.
A *ONE* bar MAP sensor will read about 4.5 or so volts under the same
conditions.
Scot Sealander
In retrospect, Scot was (is?) pretty darn savvy on our engine control systems. I'd take his word on it...
I've got the two (EFI-green & TURBO-orange) OEM MAP sensors plotted on a graph (pressure/vacuum vs. voltage at about 900 feet).
I can't post this because converting .bmp to .gif looses too much detail.
I can, however, insert this into a MS Word .doc and attach to an email.
If anyone is interested, PM me your address.
BTW there is a close 2:1 relationship between Vacuum ("Hg) and Pressure (psi). That’s why the stock boost gauge shows low negative numbers when at idle (-9 psi = 18"Hg engine vacuum).
I can't post this because converting .bmp to .gif looses too much detail.
I can, however, insert this into a MS Word .doc and attach to an email.
If anyone is interested, PM me your address.
BTW there is a close 2:1 relationship between Vacuum ("Hg) and Pressure (psi). That’s why the stock boost gauge shows low negative numbers when at idle (-9 psi = 18"Hg engine vacuum).