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You may want to ask the tuner about this:
If the EFI is using a MAP sensor and is speed density strategy, which fast used to do, they typically could get by with one MAP sensor. They did this by saving the MAP reading before the engine was started. That told the ECU what the atmospheric pressure was. If you don't change elevation too much and no huge storm front blew, in you were good.
If you drive up a mountain and see a 7000 FT change, that strategy doesn't know this happened. If you shut the engine off and then restart it, it resets the atmospheric pressure to the new elevation. If your ECU uses this strategy, this little trick is worth knowing. If not, there is no point in doing it.
Ford Mass Flow EFI systems starting around 1990 measure the mass of the air flow into the engine and use a MAP sensor not connected to the engine and all this was compensated for. Earlier speed density systems were as described above.
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