2007 4.6L ECM barometer reading problem

[Nedwreck]

My 07 4.6L ST has been giving me some fits... I had been chasing some lean codes, odd drivability problems with some sputtering and acting like it was randomly leaning out then coming back to life...

After many hours of inspecting everything, doing smoke tests for vacuum leaks, replacing injectors (which was needed), and looking at scanner readings and whatnots.. well I took it to a local shop and asked them to see what they can find.

They reported that Barometer readings in the PCM were randomly climbing as though I was going up a mountain (which doesn't make sense, I'm in a flatter part of Kentucky at about 850' over sea level). After the internal baro readings climb high enough to lean it out and spit and sputter a bit, it resets itself back to a reasonable number and runs ok for a bit again.

I'm aware that these don't have the EGR assembly with a MAP, and I'm told these vary the cam position to simulate EGR function (that seems odd to me, but ok lol). We have tried a different MAF, and exchanged the new one with another from a LAPS jut in case the new one was wonky. The tech working on this seems knowledgeable, and I can tell this is bugging him.

It seems this truck generates a fake Baro reading from other inputs, and goes with that. Does anyone know how these generate the Baro in the PCM?

Has anyone encountered this, or have any thoughts what to do with this problem? Is there a relevant sensor I'm missing?
TIA!

 

[Turdle]

I thought the maf sensor contains barometric sensor also. 6 wire sensor in air tube downstream of air filter

 

[Nedwreck]

I thought the maf sensor contains barometric sensor also. 6 wire sensor in air tube downstream of air filter

My diagrams show pins 1&2 for IAT sig and return, 3&4 for airflow reading, 5&6 for power and ground.

I don't think the 4.6l has a physical BAP sensor, but does a "logical" baro reading in the PCM somehow. I'd like to learn how it does that, if possible.