JEMERY

iTrader: (3)

Does anyone know where to find the MAP sensor calibration for the MSPNP9093? My gauge is reading a good bit lower than it should based on my altitude above sea level when car is off. Reading 94kPa should be around 99kPa.

chicksdigmiatas

iTrader: (11)

Mine does that crap too, accept it reads like 87.

Matt Cramer

Are you certain the ambient air pressure isn't actually 94 kPa today? That's a pretty common reading in the Atlanta area. The initial kPa changes with the weather, too; some days it's higher.

y8s

iTrader: (8)

29.60 inches today. that's just a hair over 100kPa.

at least near Grant Park...

http://www.wunderground.com/weathers...?ID=KGAATLAN40

JEMERY

iTrader: (3)

I'm pretty sure my map is reading quite different than the norm ATM pressure. It seems other people are having the same issue. What do we need to do to correct this DIY?

Matt Cramer

According to Freescale's data sheet, the sensor has a 1.5% voltage tolerance, which translates into about a 3.5 kPa tolerance (4.69 volt range * 1.5% / 0.02 volts per kPa). MSPNPs are based on MS1/Extra, and the calibration is hard-coded. You can recompile the code with a new MAP scaling, or accept this as a normal amount of variation between individual sensors.

JEMERY

iTrader: (3)

Ok so we need to live with the MAP variation to stay under the MSPNP warranty, fine by me. I was playing through the megatune software and was wondering if there was anyway to balance off this MAP sensor variation with a barometric correction? Is this is possible, and have you guys messed around with doing something like this?

Matt Cramer

The high-res 11 versions have a % baro mode that does what you're asking about.

chicksdigmiatas

iTrader: (11)

Ummm, mine reads between 82-84 all of the time. I also didn't know my pnp had a warranty.

Stealth97

iTrader: (5)

Keep in mind the MAP sensors do not have to be dead on. It would be nice, but as long as numbers are consistant the actual reading does not matter. For example, if your sensor read 10kpa too low all the time, that's fine, and If you tuned your car well on that MS your tune has compensated for it, however, if the real barometric pressure stays at 92 KPA, and your reading is 82 KPA at one point and 90 at another then that is a problem. Its inconsistancy that will cause a problem.

JEMERY

iTrader: (3)

Where can I get Hi Res 11, I'm having trouble finding it.

hornetball

iTrader: (4)

Necro post, but some of us are too cheap to part with our old 1st gen MSPNPs. And I'll bet nearly everyone that has an old MSPNP with it's original MAP sensor has low MAP readings. In my case, I was seeing ~86kPa on the red car and 88kPa on the silver car (key on prior to engine start -- atmospheric pressure 99kPa).

Believe it or not, this is normal behavior for an absolute pressure sensor. Modern, MEMS-based absolute pressure sensors typically rely upon a sealed vacuum reference on one side of a sensing diaphragm, with the other side open to the pressure of interest (MAP in our case -- see attached MPX4250A datasheet). Alas, nature abhors a vacuum. As air molecules leak into the vacuum reference over time, the output signal from the sensor diminishes for the same applied pressure. And the issue isn't limited to low-cost sensors, even aerospace-grade sensors for air data computers certified to 55,000 feet have this issue.

The best way to handle the issue is to provide for periodic re-calibration. Thankfully, this feature has been added to later MS generations. That doesn't help those of us nursing our older MSPNPs along though.

Some have stated that this is a harmless flaw, that all you need is consistency and you can ignore the lack of accuracy. Relative to fuel tuning, I would agree. The change in the sensor happens gradually. Assuming you periodically autotune your VE table, this will never be an issue for your AFRs. However, this can become a real problem for spark advance, boost control and overboost protection. For each of these functions, the lower-than-real pressure sensor reading cuts safety margins.

So, what to do for an early MS? One solution is to replace the sensor. I recently bought some new MPX4250s from Digikey and swapped out the sensor in the silver car's MSPNP. Not hard but tedious.

When it came time to do the red car, I figured there had to be a way to do this in software. My first attempt was to manipulate the calibration files like Matt suggested (these are barofactor*.inc and kpafactor*.inc files in your project \src directory). However, I discovered this didn't work. On the early MSPNPs, the converted MAP value is not transmitted on the serial port, rather raw MAP sensor ADC is sent. That means the TunerStudio MAP reading doesn't change -- so you'll end up with a mismatch between what is inside the MSPNP and TunerStudio -- not good.

My next attempt was simply to put an offset into the raw MAP sensor ADC at the point of acquisition. I did this with a series of inca statements. This is a screen capture showing the code diff on 029y4a software.



This worked perfectly and was a whole lot easier than replacing the sensor. With the 4-bar sensor in the MSPNP9495, each inca statement increased the reading by ~3.5kPa. The 3 inca statements corrected my pre-start MAP from 86kPa to 96kPa. You'll need to experiment with how many inca statements you need -- and also keep an eye on things in the future as the sensor continues to age.