Elevation change affecting fuel injection?

For the second time in within the past year my 99 Mazda 626 unexplainably stalled after driving for approx 90 minutes. Last August when it happened I had it towed and it later started and the mechanics couldn’t find anything wrong. Yesterday it died and wouldn’t start until this morning when I loosened, then tightened the gas cap.

In both instances i was traveling from an elevation of about 9000ft (over some 11000ft mountain passes) down to 5000ft. Has anyone heard of elevation changes affecting fuel injection? The other commonality was use of the air conditioner. I almost never run the AC but in both cases the AC had been on. My limited knowledge and research says that the AC wouldn’t cause the car to die but I thought it was an odd coincidence.

I’m curious if anyone has heard of similar problems.

It sounds like you may have a problem with the fuel tank vent system.

One of the major benifits provided by fuel injection is that a car with fuel injection does not suffer the altitude induced performance degradation that carbureted cars do.

Your car’s ECU will compensate for the reduced air density without problem. The change in altitude was not a factor.

The gas cap comment makes me also think of the EVAP system. If the tank cannot breath in, a vacuum can develop in the airspace as the gas is pumped out and make it difficult for the fuel pump to maintain pressure. You should have a CEL light. Do you? Have you checked for stored codes?

The AC system can make a difference if the engine is having difficulty operating due to some other problem or if the AC compressor is binding up. The compressor takes its power right off the crankshaft and can create too much of a load if there’s a problem.

  1. check for stored codes
  2. check the fuel line pressure and pressure regulator. A Haynes manual will direct you.
  3. get all the maintenance up to date including filters if it’s not already. The problem could be as simple as a clogged fuel filter.
  4. if it stalls again, try the gas cap trick. Let us know if that works. If it does, that’ll suggest the EVAP system and we can advise you from there.