Map calibrations

[luke2152]

Last year I had my ms2 running on boosted mx5 engine and set up really well by someone more experienced than myself. Used it on another project over the winter. Built another one to identical specs (assuming I didn't make mistakes) to put on the mx5 and have it running. Hard to start and pumps out rich black smoke. Once running it runs well although map value at idle is a bit higher than I'd expect (30kpa). Notice prior to start the map reading is 75kpa. Surely it should be exactly 100kpa (at sea level). They should both have the same map sensor (mpx4250?). Should I be trying to adjust the calibrations or should I be looking for another cause (I'm thinking battery voltage calibrations might affect the sensor). Coolant and MAT readings seem a little out as well although not wildly wrong (18c and 30c respectively prior to startup when it was about 10c). Any suggestions?

[jsmcortina]

First suggestion:
Read the "Megasquirt-2 Setting Up Manual"

Second suggestion:


James

[luke2152]

Thanks James ;)
Firstly you are bloody quick at replying.....Because by the time I managed to get the msq off my non-internet garage laptop to my surf-the-web laptop you'd already replied. Sorry. MSQ attached.

As for the setting up manual. I've read it many times in detail and managed to miss many a detail. It is a fairly specific question that I hoped someone would point out my obvious mistake.

[luke2152]

Have opened up and confirmed it is definitey the mpx4250 map sensor in there.
Is it normal for these to go bad/loose calibration somehow?

[Matt Cramer]

Failures in these are very rare - about the only thing I've seen that kills them is if they are installed pointing up on a motor with excessive blow-by and get filled with oil.

[luke2152]

Hello Matt - Thanks for reply. It is certainly working - kpa goes up or down as you suck or blow on the hose but 75kpa is clearly not atmopheric pressure. I have no blowby to speak of.

[luke2152]

I have replaced the map sensor with another mpx4250ap sensor but the problem remains. 74kpa measured atmospheric pressure. All the while my other ms2 reads 99.9kpa. The MAP calibration settings are identical on both so I'm a little confused. Could it be a hardware issue on the board?

[rickb794]

Calibration or bias resistor

[luke2152]

I can only find bias resistor option on the thermister menus?

[dontz125]

Calibration is up in the [Tools] menu in TS, but it is set to 'MPX4250' in the .msq you posted. There is no bias resistor with this type of sensor; it generates a 0-5v signal. Please measure the voltage at each of pins 1 (notch), 2, and 3 of the sensor vs the tab on the voltage regulator (pins 4-6 aren't electrical, just physical mounting).

[ol boy]

Quick math shows that it's off by nearly 1/2 a volt. 250kpa spread / 5 volts = 50kpa per volt.

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[luke2152]

Pin 1 = 1.7v
Pin 2 = 0.0v
Pin 3 = 4.9v
Measured against the centre pin of U5

[dontz125]

That SHOULD give you 95kPa ...

[luke2152]

So that would mean the problem lies between MAP sensor and the ms2 chip?

[ol boy]

That's a good start. I noticed on my V3 board 9 years ago that I had a biase of about 4 kpa low. I'm not sure why and never looked for what might cause the offset. I later went in a adjusted the values to raise the offset closers to where I'm located.

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[masp]

Got the same situation, reading 75 kpa as athmospheric pressure, as luke, changing firmware does nothing, resistance from map sensor to ms2 daughterboard 23 pin ir 989ohm, voltage at the same pin is 1.7v. Voltage at map sensor Pin 1 = 1.7v Pin 2 = 0.0v Pin 3 = 4.9v, Kpa goes up or down as you suck or blow on the hose, default calibration data shows 75 at athmospheric. Where to find problem?

[Marissp]

solved. it was bad contact from ms2 daughterboard pin1 and pin 40

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[Bmrbob]

solved. it was bad contact from ms2 daughterboard pin1 and pin 40

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Can you, or someone, expand on this. I have been having what I think is the same issue. For 2 weeks Ive been chasing my tail with the darn thing. Am getting 77kpa map reading no matte what I do. have checked ground, ecu voltage between jumper and map sensor ground, software etc etc. Have an MSPNP2 with mpxh6400 sensor.

Please! Any help would be greatly appreciated.

[masp]

I think mpxh6400 needs different calibration than standart map sensor. In my case pin 1 and pin 40 from ms2 daughterboard to mainboard was broken.

[Bmrbob]

I think mpxh6400 needs different calibration than standart map sensor. In my case pin 1 and pin 40 from ms2 daughterboard to mainboard was broken.

Hmm. There is an option for mpxh6400 under map/baro. That is what im putting it at..

Interesting. Were the pins visually broken, like fallen off? Your problem is very similar to mine. Cant get it to move from 77kpa