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karl
06-13-2010, 10:02 PM
has anyone on here with 3rd gen electronics on their engine run their engine on more than one different MAP sensor?

i'm trying to determine the variance that's tolerable in the sensors. i'm building some generic 3rd gen sensors for a vendor and i've got a sensor to use for calibration, but the owner of the sensor says that his car runs slightly differently on this one than the one that's in his car currently. i've got the new sensors outputting pretty much the same signal as the gen3:
http://img.photobucket.com/albums/v77/scarecrowX/EMS/sensors.jpg

http://img.photobucket.com/albums/v77/scarecrowX/2010-06-11164629.jpg

ignore the un-smoothness of the graphs. that's a result of the datalogger i used to log the voltages while i increased the pressure. (i used an old JAW wideband to do the logging and ran the datalog csv through excel for graphing). the red line is the gen3 MAP that i have for comparison, the blue line is the new sensor.

just curious what people's experiences are on the difference, if any, between sensors.

hopefully, when these are done, we can kiss the days of $300 MAP sensors goodbye.

v8killer
06-14-2010, 07:35 PM
nice whats the price then?

karl
06-14-2010, 09:30 PM
no idea. that's up to the vendor. i made them as a trade for goods rather than $$. i know how much they cost me to build, but that shall remain a bit of a secret :D what do you think would be a good price?

once he runs out of them, i'll probably build/sell what i have left. when i had the pc boards made, they sent me more than twice what i ordered, so i can make them up in a hurry if need be. takes me about 10 minutes to disassemble the stock sensor and solder in the new sensor board. boards take a bit longer to solder, since i was dumb and used 603 size SMT resistors. my eyes still hurt from trying to solder those in haha.

i'm also considering building a MAF translator for gen2 cars- basically a simple part that would allow the use of a hotwire MAF sensor instead of the aging and horrible AFM. depending on the MAF sensor, they can be found cheap and easy if it ever goes bad.

karl
06-14-2010, 09:30 PM
double post. why does it do that to me?

v8killer
06-14-2010, 09:38 PM
yeah, i made one but left it untested as i got a diypnp. speed density is still the easyest and safest but not as precise. you have to make a differnce inverter its pretty easy but i think you have to use 100k resistors

Sang
06-14-2010, 09:55 PM
double post. why does it do that to me?

Because it knows we have to do a double take to understand what you're saying half the time ;)

karl
06-14-2010, 10:52 PM
yeah, i made one but left it untested as i got a diypnp. speed density is still the easyest and safest but not as precise. you have to make a differnce inverter its pretty easy but i think you have to use 100k resistors

for me, SD is tougher because it would require a microcontroller and lookup tables for MAP vs RPM, and i suck at coding. a MAF translator would be easy though, since all it needs to do is modify an analog signal. inverting it is simple- 2.5v reference on the noninverting pin of an RRIO opamp and neg. feedback with no gain to the inverting input. output then mirrors input. then it's just a matter of fudging the signals to they work out the same.

i need to find a local with an AFM and install a MAF and datalog the two voltages against each other to see what's going on there. i also need to be less lazy.


Because it knows we have to do a double take to understand what you're saying half the time ;)

ironically, so do i :D

v8killer
06-15-2010, 01:42 AM
lol the difference inverter can be made to have no gain at all it takes a constant 5v to the + and the inverting or "map/maf" voltage to the - (IIRC) and what you get is (+) - (-) basically 5v- map voltage so at idle map = .8 to 1.0 v (st165 2 bar) that sub'd from 5v = 4.0-4.2v. AFM at idle is at about 4v

so at full bore map is close to 4.9v subtract that from 5v and u have .1v , full open on the AFM is .1-.5v

karl
06-15-2010, 03:20 AM
i think there are 2 problems with that method:

1. map signal is linear. AFM signal is non-linear. also, MAP has to be combined with rpm in order to get estimated airflow. 3.5V on the map sensor at 3000rpm is significantly different airflow than 3.5V on the MAP sensor at 6000rpm. that's why it would take a uC running the MAP and RPM through a lookup table to see what the AFM would read at the intersection of those two signal points.

2. the MAP signal is referenced to ground. maybe i'm not understanding your circuit well enough, but you only get one input to the ECU for map signal. the other side is tied internally to ground, so you can't put 5v on the + pin and map voltage on the - pin because the - pin of the circuit is already connected to ground. i hope that makes sense.

v8killer
06-15-2010, 04:08 AM
let me find a pic or drawing, and the ecu does take rpm into account. because the afm does stay open at almost the same rate at full boost, well, with my turbo.

http://en.wikipedia.org/wiki/File:Op-Amp_Differential_Amplifier.svg

v2= 5v
v1= map

v out = v2-v1 if all the r's are the same

karl
06-15-2010, 06:47 PM
Right, it does monitor rpm. The problem is that the MAP and the afm aren't measuring the same thing, so the signals aren't interchangeable. The afm is measuring airflow, while the map is only measuring half of the equation needed to derive an airflow signal. There might be a way to make a composite signal of both using a frequency to voltage converter for rpm, but I have no idea jhow that voltage curve would compare to the output of the afm. It would be interesting, for sure.

v8killer
06-15-2010, 07:39 PM
i know, data log the AFM signal through the rpm at various boost levels and part/full throttle

then compare that to the map sensor

karl
06-16-2010, 01:45 AM
have you actually done it? or are you suggesting that i do it? i guess i'm not sure if you're telling me i should try something or hinting at something you've already done and the very interesting results, heh.

i think the problem is the difference in what the maps in the ECU represent. both are scaled by respective load input and rpm, but when the maps are scaled by MAPxRPM, the numbers in the cells represent estimated airflow numbers. the ECU uses that cell value to calculate the base pulse width. it then uses external factors to add corrections to the BPW.

with airflow x RPM, the numbers represent desired AFR, or correction to the base pulse width to achieve the desired AFR. the ECU uses the airflow signal itself to calculate base pulse width, then uses the map to correct it for desired AFR at specific load/rpm points (richer at high boost, etc).

that's how i'm seeing it thus far, though i could be wrong. sometimes i get a bit narrow minded when i'm concentrating on something really hard. it does make sense from a certain perspective as well, since really BPW stays mostly the same across the rpm range for a given MAP column, it just increases frequency as rpm increases. there's some fudging necessary for increase/decrease in VE.

if you have that sort of data lying around, i'm all ears :D

joe's gt
06-16-2010, 06:04 AM
How is a MAF translator more advantageous than say an HKS VPC? Is it just because of a faster response and more accurate than a flapper door? Sorry for the noob question just trying to get on track with what you guys are talking about.

v8killer
06-16-2010, 07:09 AM
sorry i was saying to try it that way. i would like to know aswell but i am in the middle of a lot of stuff

the vpc is like a maf translator and come to think of it that what we are trying to get at but cheaply and still be effective

karl
06-17-2010, 02:17 AM
How is a MAF translator more advantageous than say an HKS VPC? Is it just because of a faster response and more accurate than a flapper door? Sorry for the noob question just trying to get on track with what you guys are talking about.

main idea behind a MAF translator would be to get rid of the AFM for a sensor that's more reliable, more accurate, less expensive to replace and easier to find. i doubt there's much of a market for it, but it's been an idea that's been bouncing around my head for a while now. i should probably concentrate on other stuff :D

oh yeah, finally got to test the new sensor today. worked flawlessly. video sucks (i was trying to get the WB gauge, but it just scrolls) but you can hear how well it pulled. this was in a 6th gen celica with a 3rd gen 3SGTE. drove just like the stock MAP. afr's in the mid 11's, dipping to the occasional high 10 in boost.

http://www.youtube.com/watch?v=8UeIO5XOnpc

i'm pleased. :D


sorry i was saying to try it that way. i would like to know aswell but i am in the middle of a lot of stuff


oh no worries. it's always good to get an outside perspective on this stuff too, especially from someone who knows what's going on.

i need to add an rpm converter/protection circuit to the datalogger (that's how i fried the first one) before i can log RPM, but once i do, i can log all that crap. i need to set it up with the MAP anyway to log pressure rise in the manifold between shifts with and without a BOV. i already know what that trace is going to look like, but it's nice to have graphical representation.