baro and 2bar setup

[turboberserker]

I was poking around in my 2 bar tune today. It runs pretty smoothly most of the time, but there are some head scratchers...

1) my baro (in the scanner) reads 79.7 kpa, but the baro reading today was 1019 mb (~100 kpa)
2) I used to idle at 57kpa pretty much day in day out on the Megasquirt. After the 2 bar, I'm idling at 70-80kpa which makes me think my scale value (89.3 to get to 50kpa) isn't accurate.
3) I made no MAP offest adjustment, and my stock value was +10kpa. For experinmenting with this value, it seems like I can use this value to shift the whole MAP scale around but I didn't go to full boost with it, so I wonder if its just going to cap me at 105kpa - whatever I shift towards 0.
4) from max vacuum (-18 inHg) to 0.0psi on the boost/vac gauge (Dak Digital), I see 4 psi change in the MAP reading. The thing is, that's an 18 inHg change on the guage and an 8.7 inHg change in the MAP...

Any of this make sense?

[Blacky]

4) from max vacuum (-18 inHg) to 0.0psi on the boost/vac gauge (Dak Digital), I see 4 psi change in the MAP reading. The thing is, that's an 18 inHg change on the guage and an 8.7 inHg change in the MAP...

Any of this make sense?

I can try and clarify the last point...

Using a 2 bar MAP sensor on a PCM designed for 1 bar input will cause the MAP variations to be half the real world variations.

Think of it this way:
Assume the 1-bar MAP sensor is linear and 0-100kPa = 0-5V. That's 0.5Volts for each 10kPa change in pressure.
Assume the 2-bar MAP sensor is linear and 0-200kPa = 0-5V. That's 0.25Volts for each 10kPa change in pressure.

That means when you have the 2 bar MAP sensor conencted and the MAP pressure changes by 10kPa the voltage output from the 2-bar MAP sensor will change by 0.25Volts. The PCM still thinks it is looking at a 1-bar MAP sensor and interprets that 0.25volt change for a 1-bar MAp sensor which would only be 5kPa - not 10.

Where you see an 8.7psi change on your Dak, you should see *exactly* half that on the MAP PID in EFILive. You're actually seeing 4psi which is a little under half. You may need to alter the MAP scaler to make it read exactly half.

Paul

[turboberserker]

Thanks Paul, that makes perfect sense.

So worst case, the scaler is a little off (enough to make that 4 psi = roughly 4.4psi). To correct that, I should move my key on target from 50kpa (7.2psi) to 53kpa (7.6psi)?

Would the offset change this at all?

[Blacky]

Thanks Paul, that makes perfect sense.

So worst case, the scaler is a little off (enough to make that 4 psi = roughly 4.4psi). To correct that, I should move my key on target from 50kpa (7.2psi) to 53kpa (7.6psi)?

Would the offset change this at all?

Basically what you want to achieve with the MAP scaler is, at key on engine off the MAP PID in the scan tool should read exactly half of the current barometric air pressure. Don't use the BARO PID in EFILive for barometric reference - it is calculated from the MAP sensor which you are trying to scale. You'll need an independant barometer. You mentioned the DAK - that would be ok to use as a baro reference.

The offset will not chage the scaling.
Say your MAP sensor is designed so that 0V=0kPA and 5V=100kPa

Real world application will never see 0kPa and may see above 101.3kPa (1-bar at sea level). So an offset of 10kPa just shifts the entire range from 0-100kPa to 10-110kPa i.e. 0V=10kPa and 5V=110kPa.

Regards
Paul

[turboberserker]

So say I never see less than 40 kpa, theoretically I could boost the offset to 40 and have a max MAP reading of 1.4bar on a 1 bar map (or 2.4 bar on a 2 bar)?

I've been back and forth on this for a few days ;) I know we can do it in the PCM (hell it's just software, right :P) but isn't the MAP going to max a 1bar in any case?

[Blacky]

The offset will not chage the scaling.
Say your MAP sensor is designed so that 0V=0kPA and 5V=100kPa


Sorry, what I meant to say was
Say your MAP sensor is designed so that 0V=10kPA and 5V=110kPa

Paul

[Blacky]

So say I never see less than 40 kpa, theoretically I could boost the offset to 40 and have a max MAP reading of 1.4bar on a 1 bar map (or 2.4 bar on a 2 bar)?

I've been back and forth on this for a few days ;) I know we can do it in the PCM (hell it's just software, right :P) but isn't the MAP going to max a 1bar in any case?

No to the first comment, because as you described in the second comment, the 1-bar MAP sensor will max at 1-bar. That's why a 2-bar MAP sensor needs to be fitted.

Paul

[MN C5]

Erik, the 1 bar is mechanically limited to 1 bar no matter what you do electronically in the programming. I read the LS1 Tech thread and you cant read boost with the 1 bar, not even 7lbs.

[GMPX]

Think like a 1bar MAP sensor can only be sucked in (manifold Vac).
A 2bar does that, plus it can be 'pushed' in when under boost.

Cheers,
Ross

[Nox]

if you install a 2 bar map, can you calibrate the pcm to read the boost and display it on a set of scan guages?

[Blacky]

if you install a 2 bar map, can you calibrate the pcm to read the boost and display it on a set of scan guages?

Yes, EFILive has a number of PIDs already set up for boost:

GM.MAPBOOST_DMA - although I am not sure what that one displays. I think it is only available when running EFILive's custom 2-bar tune.

CALC.MAP_2BAR which just logs the PCM's MAP value * 2.
CALC.MAP_2BAR which just logs the PCM's MAP value * 3.

You can create your own calcualted MAP PIDs to suit the MAP scaling that you set up when configuring your own 2-bar setup.

Regards
Paul