pfbz

Good thought, but my guess is that something like an autometer boost gauge is just never going to display negative pressure, regardless of the reading at the sensor, unless it is a vacuum/boost gauge.

pfbz

Hmmm... MAP should be absolute pressure.

But it still doesn't tell us what is going on. I assume at full boost it reads something like "15" (boost PSI), not "30" (total MAP PSI)?

So then the question is, Does Bully software say:

"take absolute MAP pressure, subtract 14.696, display the result", which would mean that Ford does fully compensate for altitude, or "take absolute MAP pressure, subtract absolute ambient pressure, display the result" which would mean you get 15 PSI over ambient, too bad if you are at altitude.

Or maybe the OBD data stream has a specific parameter for boost, which we still don't know if it is relative or absolute...

Deerhunter4

I'm not sure but it would not read above 15 psi at any altitude that I drove through.

NASSTY

I have a mechanical Autometer vacuum/boost gauge and it works great.

adkhunter

Drove my Eco at 12k feet up in Colorado 2 weeks ago and heading back up there this weekend and will be even higher than 12k this weekend. I didn't notice any power loss at 12k at all. Going up the windy roads in the mountains I did however use the manual shift to lock it out of trying to upshift past 3rd gear. It stayed in a stronger power range that way.

Sent from my iPhone using F150 Forum

taylori

Doesn't this answer your question? If the MAP is staying the same that means the truck is compensating for altitude. Allowing the engine to make similar power numbers at almost any altitude as long as the turbo can stay within the ECU's safe parameters.

pfbz

No, it really doesn't. MAP pressure should be absolute pressure, so the numbers displayed should range from ambient (about 14.7 psi) to full boost (call it 30 psi). But the meter is displaying numbers between 0 and 15 and calling it "Boost".

So I suspect that one of three things is happening with the Bully gauge:

1. There is a dedicated OBD parameter for Boost Pressure that Ford streams to the interface, and this is what the bully is displaying.
2. The Bully meter is itself calculating and displaying Boost by subtracting 1 ATM (~14.7 psi) from the MAP value.
3. There is a dedicated OBD parameter for Ambient Pressure, and Bully is calculating Boost by subtracting Ambient Pressure from MAP Pressure.

If it is 1, we still don't know, because we don't know how Ford is calculating their Boost Pressure parameter.
If it is 2, the ECU compensates to a total maximum MAP pressure of sea level + 15 psi regardless of altitude (assuming it can without exceeding some other threshold).
If it is 3, the boost is capped at 15 PSI above ambient regardless of altitude, and while it still will perform quite well at altitude, not as well as at sea level.

Just to be clear, if you took a standard autometer-type gauge and plumbed it to a standard pressure sensor (not the MAP sensor) on the manifold, and it read a maximum of 15 psi(g), that would be equivalent to number 3 above. This is called gauge pressure.

Deerhunter, does your Bully gauge have an option for displaying MAP Pressure instead of Boost Pressure? That would answer the question...

93Cobra#2771

iTrader: (2)

My ScanGauge E shows absolute MAP pressure in psi. At idle, MAP runs 5-9 psi according to whether the a/c is cycling or not.

Pulling my 7500# TT into the smoky mountains of east Tn , the max psi I have seen is 25psi. That is no different than what I have seen before heading into the mountains. Roughly 700' difference between the two.

So, I would have to say that the boost pressure is indeed maxed at 15 psi, no matter the elevation. So, it would appear that the turbos are indeed working harder at higher elevation.

Which begs the question, how much boost could they really produce if allowed?

Deerhunter4

No. My Bully Dog guage only gives me the option of boost.

truckerdude

You do realize that 3rd gear is not (direct) drive it's 1.52:1 so it should pull like a freight train AND suck the gas. Were you towing or just hotdogging it?