mpx4250 map sensor questions

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jasaircraft
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mpx4250 map sensor questions

Post by jasaircraft »

Hi guys,

some days ago I installed and tuned a MapEcu2 piggy back on a 98 subaru, this piggyback has a built in mpx2202ap map sensor...
Comparing specs against the mpx4250 (0-250kpa range) of the megasquirt ecu... the mpx2202ap only has a 0-200kpa range... soooo why is it that in their software they have a scale option for up to 32.5 psi???

Could we make our scale on our ecus like this or even a bigger range because of the mpx4250 specs?
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Re: mpx4250 map sensor questions

Post by dontz125 »

There is an option to calibrate your MAP sensor in the Tools drop down, and will allow the use of any device. I'm not sure where you're going with this; most of their range options seem to involve the use of a different sensor. The MPX4250AP tops out around 250 kPaA, and doesn't provide a stronger signal past that.
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jasaircraft
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Re: mpx4250 map sensor questions

Post by jasaircraft »

I wanted to know if we could maybe use our mpx4250 up to 30psi (that would cover most engine setups)... and since they have a " up to 32.5psi" option with a smaller range sensor I thought maybe we could have the same or better range with the mpx4250
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Re: mpx4250 map sensor questions

Post by jsmcortina »

Please explain how you think this could work.

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juansh2385
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Re: mpx4250 map sensor questions

Post by juansh2385 »

if you check the image you posted the map sensor mentioning has an * at the end I have work with map ecu and the 32 psi is with and upgraded optional map just like we do here... to answer your question theres no way to read higer pressure with a sensor rated for less pressure
jasaircraft
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Re: mpx4250 map sensor questions

Post by jasaircraft »

jsmcortina wrote:Please explain how you think this could work.

James
Precisely because I dont know is that I ask in this forum how on earth is it posible that this MAPecu2 piggyback can read 32.5psi with its mpx2202 sensor...
juansh2385 wrote:if you check the image you posted the map sensor mentioning has an * at the end I have work with map ecu and the 32 psi is with and upgraded optional map just like we do here... to answer your question theres no way to read higer pressure with a sensor rated for less pressure
No man, look at the fifth point, where it says "-25.5inHg to +32.5psi in 2.5psi steps for medium boost engines"

Im not trying to do any harm here people, im just trying to learn...
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Re: R: mpx4250 map sensor questions

Post by masterx81 »

When the sensor is reading it's maximum pressure (200kpa in this case) the output signal will be at it's maximum value (near 5v). There is no way to read past that. You can chech it with a multimeter. If a sensor has a "maximum value" is because has a limit. No option in ecu can increase that limit. The only thing you can do for read more kpa than that is change the map and scale in software the new 0-5v voltages to correspond the new limits of the map sensor.
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dontz125
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Re: mpx4250 map sensor questions

Post by dontz125 »

jasaircraft wrote:Precisely because I dont know is that I ask in this forum how on earth is it posible that this MAPecu2 piggyback can read 32.5psi with its mpx2202 sensor...
No man, look at the fifth point, where it says "-25.5inHg to +32.5psi in 2.5psi steps for medium boost engines"

Im not trying to do any harm here people, im just trying to learn...
I just pulled up the data sheet, and the calibration sheet stops at 29psi absolute. I'm sure that the folks at Freescale would LOVE to find out how these people got (accurate and repeatable!) readings of 32.5 psi GAUGE (!) out of their sensor.

Either the sheet from MAP-ecu is wrong, or they're reality-challenged.
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jasaircraft
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Re: mpx4250 map sensor questions

Post by jasaircraft »

hahaha yeah, exactly thats what I thought... its imposible.. but of course there are always things we dont know thats why I wondered this...

I will put a mityback pressure pump next time this ecu comes for a remap and bigger turbo, and I will give it a try with the pump to see if the ecu actually reads what the pressure pump is outputting... which will most probably end up in :lol:
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Re: mpx4250 map sensor questions

Post by racingmini_mtl »

jasaircraft wrote:... which will most probably end up in :lol:
Or a broken sensor.

The only way to cover a larger pressure range is to use a different sensor. There is absolutely nothing the ECU can do to change the range of a MAP sensor. It can only change its calibration curve to read a different sensor.

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jasaircraft
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Re: mpx4250 map sensor questions

Post by jasaircraft »

For some reason, sometimes we find things we cant explain... This MAPecu2 equipped Subaru came back in for a retune using 50/50 avgas/alcohol.

While doing all the checks on spark plugs etc etc, I checked the vaccum hose that leads to the mapecu2 map sensor, I use a Mytivac pressure pump that has a very good gauge up to 30psi (compared against severall other brands of pressure gauges) for any leaks on the vacuum/pressure hose that could missguide me.

Well, there were no leaks, but while at it, I remembered this post and took a test on the mapecu2 to see if it could actually "see" above 200kpa or what the sensors limit was mentioned previously on the post.

This surprised me, it read up to 30psi with no problem, the subaru has two other guages reading the same so I could compare, that is 30psi gauge.
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Re: mpx4250 map sensor questions

Post by Matt Cramer »

The mpx2202ap sensor is a totally different scale; it's rated from 0 to 40 millivolts. (Talk about no resolution!) It is possible its scale actually extends past this at higher pressures.

MPX2202 data sheet
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jasaircraft
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Re: mpx4250 map sensor questions

Post by jasaircraft »

So because the scale is so small we cant use them? the strange thing is, it says 0-200kpa 0-29psi... whats up with vacuum? is vacuum 0v?
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Re: mpx4250 map sensor questions

Post by Matt Cramer »

The scale is 0 volts at total vacuum and 40 mV at 200 kPa. It is possible the sensor might keep going and hit 60 mV at 300 kPa. The data sheet doesn't say what it does when it goes off the end of the curve.

Such a sensor would be an exceedingly bad idea to wire up like a normal MAP sensor, but might be usable with some sort of op-amp circuit. The key here is that this thing isn't an MPX4250.
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jasaircraft
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Re: mpx4250 map sensor questions

Post by jasaircraft »

muahahaha :twisted: maybe buying one for test purposes... what sort of op-circuit? I guess calibration in software wouldnt be easy as its only 60mv?
KDW
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Re: mpx4250 map sensor questions

Post by KDW »

I have a question for this MPX4250 MAP sensor...same topic...so maybe its better to post it here than under a new topic

My question is....what If I still use this MPX4250 MAP sensor...when my engine is boosting to 35PSI already?

What are the negative effects?....

When im in max boost of 35PSI....it still just scales up to the highest reading it can read. Yes it will be too rich on lower boost but will there be a danger of a malfunctioning MAP sensor thereby will cause a lean out and destroy my turbo engine?

Thanks in advance :)
grom_e30
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Re: mpx4250 map sensor questions

Post by grom_e30 »

MPX4250 only goes to 250kpa aprox 21psi of boost so from 21-35psi the sensor will not be able to detect changes so not really a good idea.
1990 bmw 320i daily driver with m20b25 ms3 sequential fuel, 380cc injectors, d585 coil near plug, home made cam sync, launch control, fan control, vss, homebrew egt logging what's next????
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Re: mpx4250 map sensor questions

Post by KDW »

grom_e30 wrote:MPX4250 only goes to 250kpa aprox 21psi of boost so from 21-35psi the sensor will not be able to detect changes so not really a good idea.
Then if lets say I just use it for drag racing that boost always goes quickly to 35PSI....If I just tune the 250Kpa range to the proper air fuel ratio for 35PSI boost it will still provide the proper fuel. Actually im still using the stock MPX4250 MAP sensor at 35PSI for a month already. The only problem is if my boost is down to lets say only 25PSI...the air fuel ratio will be too rich for 25PSI. Am I right here?

Or theres still a negative side on this other than what I said above? Like for example....blowing up the sensor and will cause erroneous reading and thereby resulting to a lean out?

Thanks for the quick reply :)
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Re: mpx4250 map sensor questions

Post by jsmcortina »

That's a really poor idea. Use a sensor that covers your working pressure range. Anything else is a bad bodge.

James
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Matt Cramer
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Re: mpx4250 map sensor questions

Post by Matt Cramer »

KDW wrote:
grom_e30 wrote:MPX4250 only goes to 250kpa aprox 21psi of boost so from 21-35psi the sensor will not be able to detect changes so not really a good idea.
Then if lets say I just use it for drag racing that boost always goes quickly to 35PSI....If I just tune the 250Kpa range to the proper air fuel ratio for 35PSI boost it will still provide the proper fuel. Actually im still using the stock MPX4250 MAP sensor at 35PSI for a month already. The only problem is if my boost is down to lets say only 25PSI...the air fuel ratio will be too rich for 25PSI. Am I right here?

Or theres still a negative side on this other than what I said above? Like for example....blowing up the sensor and will cause erroneous reading and thereby resulting to a lean out?

Thanks for the quick reply :)
The biggest problem here is not what if your boost is down to 25 psi... it's what if the boost accidentally spikes up to 40. If that happened, you would be running lean with too much timing instead of rich with too little.
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