How are Ambient Air Temp and MAP measured?

[TexasBlownV8]

How are MAP and Ambient Air Temp values read by the PCM?

The PCM has PID values for AMBIENT air temperature, and map pressure as well. How are these values measured, or if inferred, what are they calculated on?

For MAP, the ONLY vacuum connections we have are to the Fuel Rail Pressure Sensor (with fuel pressure and fuel temp signals only), and to the EVAP solenoids (enable the solenoid).

This relates to thread about where is the MAP sensor:
http://s197forum.com/forum/showthread.php?t=43609

I'm seeing a pending DTC of P0106 MAP sensor circuit open.
We have no EGR and no explicit MAP sensor. But, the IMRC could be used to infer MAP I suppose, but that's been deleted long ago in my car.

Just recently, the Barometric pressure PID, which is supposed to be an inferred-from-MAP value, is no longer reading properly. With no explicit MAP sensor, how is this being read? Internally in the PCM? Something isn't right somewhere. It used to read properly, too.


And, back to Ambient Air Temp, that I think is internally-measured in the PCM, but not certain about that.

 

[TexasBlownV8]

Update: I tried disconnecting the battery for 30 minutes, replugging the connectors to the PCM, reconnected the battery, checked the Barometric reading, still stuck open, reading its default base value.

On the 4.0L V6, there's 2 OBDII PIDs, one for Barometric pressure, one for intake air pressure (read from the EGR system on the intake manifold). Of course on the 4.6L there is nothing to read the intake air temp. But regardless of engine, there still is reading barometric pressure.

I've looked through the wiring diagrams, components, etc. and do not see anything that resembles reading barometric pressure nor intake pressure (MAP).

Someone has to know SOMETHING!

 

[dysan]

I don't think there is a MAP reading on the 4.6. The IAT's are read though the MAF, that's why when someone relocates the IAT sensor they have to cut or de-pin 2 wires from the MAF and run them to the new IAT sensor.

 

[TexasBlownV8]

MAF/IATs are easy, as they have their own explicit sensors.

But there ARE environmental readings too, that the PCM gets somehow, for AMBIENT AIR TEMP and BAROMETRIC PRESSURE. These are unrelated to MAF/IAT.

...but, I'm wondering if ambient temp isn't inferred or calculated from IAT or fuel temp or something....or if it's measured inside the PCM case. My ambient temps are pretty high now, much closer to IATs, which are measured right on the intake manifold after the blower.

There was this OBD specifications document for 2005 YM I found and have, but it's generic to all Ford systems. It only mentioned Barometric getting inferred from MAP values, which are read an/or inferred from the EGR system. The IMRC, in the wiring diagram, says it is used to infer EGR flow. We don't have an explicit EGR system, and if you delete the IMRC (as I've done long ago), there should be no MAP readings. But, there are, as you can datalog them, and see the values change with vacuum/boost changes.

I'm going to figure this out and find out wtf is going on!

 

[lito]

MAP is inferred, so BP. Also ambient.

 

[dsmx17]

ambient temp seems like an irrelevant sampling since the ecu should run based on actual (or simulated) IAT's wish I had an answer for you still kinda new to fords