MAP sensor scaling Lb7 2002

[N2BRK]

I'm having some confusion. My truck is the '02. The MAP reads pressure, and then the BARO adjusts it for ATM, right? So wouldn't the MAP sensor need to output in PSIA and then the Baro sensor adjusts it to PSIG for a Boost reading when I log/scan? I ask because I am looking to swap and rescale my MAP for higher boost, and Lowdoller's sensors all report PSIG. I expected their MAP sensors to output in PSIA and Boost sensors to report in PSIG.

Or do I just adjust for this in my scaling, eg. if at a certain voltage the LD MAP reads 10psig, I scale that as a 24.7psi instead of 10psi in EFI Live? I am probably making this harder than it needs to be, LMAO. Thanks in advance

 

[DAVe3283]

The MAP (Manifold Absolute Pressure) sensor reads absolute. Technically it reads kPa natively inside the ECU, but most people have EFILive display it as PSIA. The Baro sensor is just another 1-bar MAP so the truck can compensate for altitude without having to come down to an idle to get a new read on the atmospheric pressure. The LB7 doesn't really do much with the baro data besides switching to high-altitude fuel limiters.

l run a LOWDOLLER 899006 (6-bar) MAP sensor on my truck and it works just fine. Their website and documentation is confusing, and I suspect they don't fully understand the difference between absolute and gauge pressure. But I can confirm their MAP sensors are actually absolute, not gauge.

To scale the sensor in EFILive, you will set the 0.5V and lower to 0 PSIA, then set 4.5V and higher to the rated pressure of the sensor (87 PSIA for the 6-bar), then have EFILive linear interpolate between 0.5 and 4.5V. That should get you really close, but on the high range sensors like my 6-bar, I had to fudge things a little bit to get the MAP to correlate to the Baro correctly. If you happen to get a 6-bar I'd be happy to share my calibration table.

 

[N2BRK]

Thanks, Dave. I'll send you a PM if you don't mind

Edit: The confusion was because LD rep told me that ALL of their gauges are in PSIG only and I thought to myself, "then why offer MAP and boost gauges"? I'll explain better in PM. Thanks! WKS

 

[DAVe3283]

I'll post it here, I'm not trying to keep it a secret
Just have to do it tonight after work, don't have my laptop with me today.

 

[N2BRK]

Since EFI Live won't scale below 0kpa, I changed all negative values to zero. Lowdoller says their 6bar's 0-5vdc is -25.38psi to 83.37psi. I changed it to kpa and the equation I used is y = 149.96096x - 174.98893 .

EFI Live used to max at 500 but they sent me a patch to bring it to 1024kpa. So if someone wants to go to a 10 bar, they could.

How does this look?

 

[Bdsankey]

Does it successfully report ~72.5psia in EFILive? I ask since the sensor is -1bar absolute (-14.5psia) to +5bar absolute (72.5pisa)? I would imagine that if the sensor is just scaled as 0<>+6 BAR instead of -1<>+5 that the readings wouldn't be accurate would they? I should have a better grasp on the sensor but that's something I haven't played with.

I would imagine it would be more accurate if scaled as 1.16V = 0 PSIA and 4.5V = 72.5PSIA per their scaling values?

https://lowdoller-motorsports.com/c...-psi-to-14-7-psi-5v-crankcase-pressure-sensor
-14.5 PSI = 0.5 Volts, 0 PSI = 1.16 Volts, 72.5 PSI = 4.5 Volts

 

[DAVe3283]

I'll post up the table I use tonight, but I can confirm the lowdoller 6-bar MAP actually reads 0 to 6 bar absolute, and I am 90% sure the 0 bar/0 PSI point is 0.5 V.

EFILive / the LB7 operating system expects the table to report absolute pressure. Don't worry too much about what you read on lowdoller's site, IMO they don't really understand the difference between absolute and gauge pressure. Luckily, the Chinese company who actually makes the sensor does know what a MAP sensor is, and makes them correctly.

 

[Bdsankey]

I'll post up the table I use tonight, but I can confirm the lowdoller 6-bar MAP actually reads 0 to 6 bar absolute, and I am 90% sure the 0 bar/0 PSI point is 0.5 V.

EFILive / the LB7 operating system expects the table to report absolute pressure. Don't worry too much about what you read on lowdoller's site, IMO they don't really understand the difference between absolute and gauge pressure. Luckily, the Chinese company who actually makes the sensor does know what a MAP sensor is, and makes them correctly.

10-4! Just asking for clarity.

Do you know at what point the ECM will get "pissed off" or what it's max value is?

 

[DAVe3283]

10-4! Just asking for clarity.

Do you know at what point the ECM will get "pissed off" or what it's max value is?

Almost all the expected boost tables are a uint8_t (0-255), natively in kPa, so any time your actual MAP measures over 255 kPa (37 PSIA, ~22 PSIG) you will fail the diags. Luckily, GM appears to have written the OS to handle the boost sensor being higher than a uint8_t can represent, and I have never had any issues with the MAP sensor being able to report huge values.

I usually handle the failing boost diags by allowing massive overboost (or even just disabling the overboost DTC entirely), but I like to keep the underboost diags enabled That way if I get a small boost leak it'll pop a check engine light and I can dig into it, rather than waiting for it to get so bad I notice the change in driving experience or smoke/EGTs.

On different turbos and/or cams than stock, that means the shape of the expected boost tables is totally different, so I like to disable the diags, then go log some long trips with the truck, ideally some empty, some towing, and some HEAVY towing on hills. I then use the logs to back-calculate the expected boost tables, and re-enable the diagnostics (at least the underboost diags).

 

[DAVe3283]

OK, here is the scaling I use for the LOWDOLLER 899006 (6-bar MAP). Looks like I did leave it scaled linearly all the way to 5.0V, but I wouldn't trust any reading above 4.5V to be accurate.

Spoiler: Text values if you want to copy/paste

LABELS    Boost Sensor Scaling (kPa)
Boost Sensor Voltage    Value
0.00    0.000000
0.16    0.000000
0.31    0.000000
0.47    0.000000
0.63    20.500000
0.78    43.000000
0.94    67.000000
1.09    89.500000
1.25    113.500000
1.41    137.500000
1.56    160.000000
1.72    184.000000
1.88    208.000000
2.03    230.500000
2.19    254.500000
2.34    277.000000
2.50    301.000000
2.66    325.000000
2.81    347.500000
2.97    371.500000
3.13    395.500000
3.28    418.000000
3.44    442.000000
3.59    464.500000
3.75    488.500000
3.91    512.500000
4.06    535.000000
4.22    559.000000
4.38    583.000000
4.53    605.500000
4.69    629.500000
4.84    652.000000
5.00    676.000000

Looks like I haven't logged above 500 kPa on the compound setup, but I seem to recall it did on the big single and didn't have any issues. Here's it at 494 kPa (71.6 PSIA / 58.5 PSIG) from a quarter mile run a couple months ago:

 

[N2BRK]

EFI live with the update. 1024kpa limit. V8 only.

 

[N2BRK]

Our numbers are so far off.

 

[DAVe3283]

It looks like you were entering it as a [email protected] to [email protected], which is relative pressure. Instead use 0 to 600 kPa absolute, which will get you the table I run. Though I recall shifting mine a tiny amount (a fraction of a percent) to get the MAP to match the barometric pressure exactly. It's normally within 2 kPa running this table.

Sent from my FlashScan V2 using Tapatalk

 

[N2BRK]

hmm. I used Lowdoller's 6Bar 0-5v instructions - [email protected] and [email protected]. I converted to KPA in EFI Live's conversion table, and then that gave me: [email protected] and [email protected]. I did the slope intercept and came up with: y = 149.96096x - 174.98893.

I ran the formula in a spreadsheet program and then for every negative number I replaced it with a zero.

I have a 100psi boost sensor for my Edge cts2, so I could try this in my MAP and then adjust the slope until they (hopefully) agree, lol.

 

[N2BRK]

I haven’t bought the 6 bar yet, but I did hook up the Lowdoller 100psi to the low pressure turbo. I injected air to the inlet of the s475 from my compressor and called up three sensors. Edge 0-100psi, factory MAP, and the LD 0-100psi. FWIW, the Edge and Map agree and the LD reads a lb high. Map is 11, Edge is 11.4, and LD is 12.3. Close enough. With this info I can start adjusting my wastegate.