One of the helpful AE guides suggested reading Exhaust Back Pressure (EBP), Manifold Absolute Pressure (MAP) and Barometric Pressure to check they're within +/- 0.5 psi of each other.

EBP- 14.7
MAP- 12.3
Baro- 14.3

What would cause the difference between EBP and MAP?

 

Jeremy, if you check that again, you should find that those three readings are roughly the same when the engine is off. Doesn't apply once you start the engine. Baro is the atmospheric pressure so it is what it is regardless of what the engine does. MAP is boost plus baro. EBP is what your exhaust manifolds see (pre turbo). So, when the engine is off the pressure inside the exhaust manifolds matche baro. Once you start the engine the pressure changes to match whatever is generated by the exhaust gases. If your EBPV closes, the pressure would increase because the engine is pumping out exhaust and the EBP valve is keeping it contained in the turbo and manifolds.

Hope this helps.

EDIT: One more helpful hint...if you don't have a boost gauge, you can select Manifold Gauge Pressure in AE and that will tell you boost. AE calculates that figure by subtracting Baro from MAP.

 

Took those with engine off, dead cold.

Yup, understand that one.

I figured out baro from the airport reading, converted in Hg to PSI.

Good to know.

And this is the crux of my poorly worded initial q. Since I took these with the engine off, after cold soaking all night, "they" said the readings should be w/in .5 psi? But they're not, so why not? Restriction somewhere? EBP tube or something like that?

Makes sense.

Yup, sure does.

I don't have a gauge, so I will be using this tidbit when logging runs to see how things are doing.

ADDITIONAL- Any ideas if you can use AE to detect a boost leak? I know, I know, build/buy a leak detector but . . .

 

Oh, ok. I just assumed that you had the engine running. My bad.

So, sounds like your MAP sensor is suspect. Now I am curious what your Manifold Gauge Pressure reading with KOEO is. When you start the engine, at idle the MAP and Baro should be about the same. Does your MAP reading change with the engine running?

 

Jeremy,
I was messing with AE today myself so I thought I'd look into this further. Now I understand your comment about getting the baro reading from the airport...because AE only give us baro in volts. I wonder if there is a conversion formula that works for that sensor?

Did you check what the reading was for "Intake Manifold Absolute Pressure"? I wonder what that is and why it's different from "Manifold Absolute Pressure"? I checked my truck today and here were my readings with KOEO:

• Intake Manifold Absolute Pressure=13.77 psi
• Manifold Absolute Pressure=13.9 psi
• Exhaust Back Pressure=14.64 psi
• Manifold Gauge Pressure=<0.07 psi>
• Baro= 4.36 volts

I am trying to imagine a way for AE to sense a boost leak but I just don't see how that could be possible. We would need a sensor at the compressor to compare to the MAP in order to sense boost. Building a boost detector is the most practical method I am afraid.

Sometimes you can use sensor readings to derive something that is not listed. For instance, when I first got my AE the choice for Torque Converter slip desired was shown but Torque Converter slip actual was not. However, I was able to figure it out by putting up engine RPM and Turbine output shaft speed and could see when the TC was locked. Eventually, with one of the recent updates, Torque Converter slip was added and now I am able to select and monitor that function.

I have also discovered that some functions appear depending on what year you pick. For instance, Transmission fluid temp in degrees does not appear when choose 1999 model year. I only get that reading in volts and have to use the converter program to figure out the temp. However, if I choose 2000 model year...then I get the reading converted for me in degrees. Weird.

So, now I am wondering if we can get baro in psi by choosing one of the later years when we connect? I think I'll try that tomorrow.

 

I'll look at the various pressures tomorrow- cold, idle and running.

There must be a conversion table somewhere for baro volts to psi, I just couldn't find one. Then I just relied on a local weather reading.

Boost leak- I'm coming to the same conclusion about just building the darn thing. I wanted to find an interpolation method but it doesn't seem possible. Oh well.

Thanks for the help. I'll let you know what I find.

 

Your EBP, MAP, and baro all all w/in .5 of each other while mine are not.

Engine Off:
EBP- 14.7
MAP- 12.3
Baro- 14.35

At idle:
Intake MAP- 12-ish
MAP- 12-ish
Manifold Gauge P- <.25>-ish
EBP- 19-ish
Baro- 14.35

At 2000 RPM-
Intake MAP- 16-ish
MAP- 16-ish
Manifold Gauge P- 3 to 4-ish
EBP- 20-ish
Baro- 14.35

Seems like two things-
1) MAP seems too low.
2) Manifold Gauge Press seems too low, which makes sense with #1.

So, I need to read up on the MAP and what it does/measure/input used for and then figure out if I'm not making enough boost. If you have ideas, I'd love to hear (read) them.