2006 Explorer XLS misfiring/elevation issues

[brewdude]

Hello all. Hopefully someone can help me out with this one...

So on top of numerous other issues I have encountered with my Explorer, this one really boggles me. I live in Flagstaff, AZ elevation:7,000 ft. Last summer I traveled two hours south to Phoenix which is about elevation 2,000 ft and as soon as I got into the valley my truck began to misfire. Of course it was hot as HELL (usually about 20 degrees warmer down there) so that might be a factor as well (Vapor lock???). But I lived in Phoenix for two years with this vehicle and never had this issue in the past.

So, I took it immediately to a mechanic and he determined that it was the "Fuel Pressure Drive Module" part #6L2Z9D372A . And Im sure he was accurate that this was in fact the problem because he messed around with it a bit and it temporarily ran a bit better. Anyhow, that part was not available in the whole state of AZ so I continued on my way back up to Flagstaff and guess what? It ran just fine up here with no misfires what so ever!

I located the part and had it shipped. I installed it (located inside the rear interior quarter panel of the trunk). I traveled back to Phoenix this last winter twice. First time I had no issues. Second trip back in April the same issue began again. Back up in Flagstaff, no issues.

So what the hell is going on????? Computer? O2 sensor? More fuel issues? Any help is appreciated.

A little back round on this vehicle. 2006 XLS 110,000 miles. Bought in 2008 with 67,000 miles. Since owning I have had to replace...

-fuel pressure drive module
-Some transmission sensor. (Truck was jolting in reverse. over $1000. seems others have had same issue and Ford wont recall it)
-Blend door actuator
-misc. steering components
- Radiator at 98,000 miles. And its starting to leak again... Again, another common issue for this year
- Radiator thermostat housing. Replaced just last weekend as this left me stranded in the middle of the desert over heated.
-and many other little issues

I should note that I take care of my vehicles, don't beat on them or abuse them

 

[Flag Gibby]

A couple of questions: when was the last time you changed the fuel filter and have you tried cleaning the MAF sensor and the throttle body? Also, I would check the fuel pressure at the split fuel rail to see where it is at to see if you have a possible fuel pump issue. As far as the cooling system leaking again goes have you ever replaced the radiator cap?

 

[MNgopher]

What octane gas are you using? I'm guessing they sell 85 octane at that altitude in Flagstaff as regular (as they do all over the high mountain west).

When you take that stuff to lower altitude (and higher heat) fuel can become an issue.

As an example, whenever I am leaving Denver to head back to the flat states to the east, I make sure to fill up with 87 octane (midgrade in Denver) to avoid the issue you sound like you are having.

 

[Flag Gibby]

85 octane is not allowed in Arizona, lowest sold octane is 87.

 

[MNgopher]

While Flag Gibby is correct that 87 octane is the minimum by law in Arizona, there was also a publication by the weights and measures department about recently catching retailers not selling the octane rating they were advertising. See:

https://www.azdwm.gov/sites/all/themes/azdwmomega/documents/BlendingOctane.pdf

Note this was just in February. I'd surmise this would be easier to get away with in Flagstaff where the altitude would generally hide the suboctane issue until you went to lower altitudes...