How To: LMM OS - MAP Scaling

[2004LB7]

My truck won’t see over 46psig

I calculate 2.17 volts at 46 psi. maybe you can check that with your compressor and see if it is accurate enough

it is right in the middle of the large jump you have in the original numbers so you cant see anything else close to compair

my guess is that the sensor works somewhat like a variable resistor. less in = less out. unless there is some kind of regulator built in but then I would expect it to be a three wire connection with a supply, return and ground. but because google returned no results I couldn't check myself. also I would suspect you would never get 5 volts out on a regulated sensor if 4.8 is within spec. I would guess it would stop at some voltage close to its minimum specified voltage. I think you can use the numbers I provided without any issues.

 

[kidturbo]

Glad to see someone else putting in hours on this one, I'm wiring up a couple 10 bar MAP setups this week..

It's been a couple years since I last set down at the table to hashed this out the first time. So please forgive me if I don't seem to recall much detail. But here is what I know about the scaling.

It's best to scale everything in KPA, because 0 psi on a gauge, isn't actually the same as 0 bar or 0 kpa in scientific scale. Zero on a analog gauge is somewhere around 1 bar on these sensors.

If you look at the first values of a STOCK 3.5bar sensor in my pic above, at 5V it's 366.70 kpa, or 3.66 bar. So GM also guestimated, or extended the table beyond sensor output range. See values on the sensor box compared to what Brayden supplied me.

Last, if you want to verify how close your values are running to any sensor rated scale, substitute the sensor with a POTs on a live ECM and read GM.MAP2 values.

At this point the ECM still only accepts values up to 400kpa for fueling tables. So this mod is actually lowering resolution used in fuel calculation, in exchange for logging higher values on the CANBUS. Would be nice to raise that 400kpa limit to match.

 

[2004LB7]

So the sensor is reading PSIA?

 

[kidturbo]

Best I recall. I know for certain the ECM uses KPA values in the code, and when you read map2 with key on engine off, OEM sensors read mid 90's in my neighborhood, or about same as BARO..

 

[N2BRK]

good info! I'm at work now, but I'll re-read and re-test (I hope tonight). It does change everything though - McRatt gave these figures in PSIG in his post, and I just copied that idea...so I'll have to adjust all of my PSIG readings to PSIA or convert to Bar.

 

[2004LB7]

Just add 14.7 to convert to PSIA. But retesting may not be a bad idea

 

[N2BRK]

I think so. My goal is to give back a little so that anyone can read this thread and buy the same part and plug in my values and have a nice day :hug:

 

[kidturbo]

Just add 14.7 to convert to PSIA. But retesting may not be a bad idea

Actually it's 14.5 psi to 1-bar, or 100kpa. According to my unit converter app..

 

[2004LB7]

Thats probably with the sensor held above your head while on your roof top jumping in the air. For us fokes who lay on the beach use 14.7

Actually a fixed value of 14.5 is probably better anyways as most are at least a little above sea level. If I'm not mistaken, I think GM uses 14.5 also

 

[N2BRK]

OK! I had some fun outside I powered up the sensor from the truck's MAP sensor wiring. Voltage was 4.96vdc on my Flounder (My chinese excuse for a Fluke).

The numbers do change slightly compared to the indoor test off the 4.8v power source. Very slight changes, but certainly more accurate data.

This time I set up a super slow leak and watched the voltage and pressure ride down together. I took samples along the way and found everything very linear until you hit 113psig then the reading hits 4.92vdc and holds all the way until I measured 112psig and stopped.

Data set: PSIG/VDC (yes I'll need to update for PSIA)

0,.45
27.0,1.52
27.5,1.54
28.0,1.56 <--- low point on cax file to enter
28.5,1.58
29.0,1.60
29.5,1.62
30.0,1.64
30.5,1.66
31.0,1.68
31.5,1.70
32.0,1.72
32.5,1.74
33.0,1.76
33.5,1.77
36.0,1.87
44.0,2.19
44.5,2.21
46.0,2.26
46.5,2.28
47.0,2.30
47.5,2.31
48.0,2.32
59.0,2.78
83.0,3.73
82.5,3.71
90.5,4.02
100.0,4.41
110.0,4.82
111.0,4.84
111.5,4.86
112.0,4.88
112.5,4.90
113.0,4.92 - all over now, max voltage output
116.0,4.92
121.0,4.92

Later tonight I'll have to re-calculate the slope and predict 5v. I'll also need to convert from PSI.

 

[N2BRK]

If I use points at 0psi and 100psi, I get 114.899psi, 5vdc
If I use points at 28psi and 100psi, I get 114.90psi, 5vdc
If I use points at 28psi and 112.5psi, I get 115.03psi, 5vdc

The numbers look better than last night. Very linear until the plateau. I'm pleased. Now to fix to PSIA...

For the cax file, I'll use 1.56vdc reading at 47PSIA
And I'll use 5vdc at 129.5 PSIA

Maybe it'll even work, LOL. Yes?

 

[N2BRK]

shit - convert to kPa!

324.054 and 892.871

 

[N2BRK]

Not there yet. I’m showing 37psig on the truck when I turn the key on.

 

[kidturbo]

Finally got chance to test these sensors running. Before installing on engine, I tested scale on bench with volt meter and air compressor. The sensors scale reads in atmospheric, not true pressure like a stock GM sensor. So you have to adjust map accordingly. But after a little playing around, I got em reading within 1kpa of the baro on ECM pids.

That said, I'm not sure a 100psi is good choice here unless your running compounds making over 90PSI boost. In my case, without a MAF, this lower resolution with higher psi scale may be causing an issue at off idle spooling territory. Need more testing, but I'll work it out next week and let ya know the findings. A 6bar might be a better choice, but finding one with correct connector and thread size from Honeywell is about impossible. Looking at other sources.

For now see scaling below. Which is very close, but I then added a couple lbs to top end numbers to get my MAP and BARO lined up perfectly on the ECM at 700fl elevation.

-K

 

[thahn8991]

Just wondering if anyone has this for any of the LBZ OS or the addresses that need to be changed to to be for the CAX to be compatible with the LBZ OS. Any help is appreciated Thank you.

 

[Steven P]

Has anyone found numbers that work with 5bar map sensor for the cax files? Working with a lowdoller motorsports 5bar.

5 Bar MAP Sensor (-1 to +4 Bar Map Sensor) PN: 899005

5 bar map sensor. (-1 bar to +4bar) -14.5 PSI to +58 PSI Absolute pressure sensor -14.5 PSI = 0.5 Volts, 58 PSI = 4.5 Volts Outputs 0.5V to 4.5V Input 5V Accuracy 0.5% of full scale. Heavy duty Stainless steel body 1/8" NPT thread Includes GT150 packard connector with pins, and grommets...

lowdoller-motorsports.com

 

[malibu795]

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