Losing altitude

Aloha
I have a 1996 Discovery SD with a 4 liter V8 injected and four speed automatic. When I drive up hill over 1000 feet higher the vehicle begins to intermittantly decrease in power and the check engine light comes on, flashing the last time, then staying on. The computer monitor indicated an ignition fault, there have been no problems with starting. The spark plugs were changed and were fouled indicating a rich gas/air mix. The mechanic knows several things that could cause this, but does not want to begin replacing parts until he finds it. Has anyone heard of a similar problem?

Sound to me like your LAN sensor in the exhaust is not working correctly, the LAN sensor detects rich fuel mixture and should automatically make the ECU componsate so that the AIR/FUEL is correct.
You will get this problem due to the OXYGEN level in the air at altitude is reduced and will make the engine run richer.
have you also checked the air filters if these are getting dirty these will also reduce the efficiency of the AIR/FUEL mixture.

ah dint really think 1,000ft is high enough to worry about lack of oxygen , not when you consider that most of the lake district is higher than that.

Consider changing the HT leads also. As the leads break down the spark gets weaker and can cause rich running. (People have told me this is absolute rubbish but I promise you from experience it really works. Leads only seem to be good for about 50 000 miles).

BigIslander again
two codes now P1313 misfire catalyst damage fault Bank A, P1364 no ignition coil 4
Does this affect an analysis of the problem.

I agree with Slob... When in the Alps, at 2000 metres (i.e. 6000 feet) or above, you do notice a lack of power...it's really almost 3000m (~10,000ft) before the oxygen deficiency should cause significant issues (i'm a mountaineer)...

Are you sure the problem relates to altitude, rather that a long uphill route (some sort of fuel starvation maybe because the engine's higher than the fuel tank going up a long ascent...)?