The Effects Of Altitude

We recently got back from a trip from NC to TX to visit relatives and of course took our camper. I saw a difference in the fuel mileage after the first day - first day 15mpg after that I got about 12mpg and the power was down. I was sure that I had damaged the catalyst pulling the camper in the mountains in Alabama, the old 4.0 ohv was working hard to pull the hills. Got home ok and started to diagnose the power/mileage problem and the cat was not hurt. Since I have some scanner software for my laptop I checked the data on the engine and noticed that the computer thought I was still in the mountains (since there is no map sensor on the car the computer uses the wide open throttle value to determine altitude). All I had to do was remove the battery cables for ten minutes and reconnect to fix the problem (yes, I know some scanners will reset the value but what I have won't). I've turned wrenches for 40 years and never would have thought to try this if it were not my own truck and I had plenty of time to think about it.

 

[2000StreetRod]

Pid?

I was under the impression that since your engine has a mass airflow (MAF) sensor it is unnecessary for the PCM to compute altitude to determine the A/F ratio. I have a Dyno Scan PC based scanner application and it lists no parameter identifier (PID) associated with altitude. What is the name of the PID on your scanner application associated with altitude?

 

[drbenz]

It's the baro pid, Ford says that you can reset it by doing three or four wot runs but I wanted to clear fuel trims and everything all at once.