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Car Dying at high elevations / Vapor Lock?

Recently, my 1988 Isuzu Trooper began dying at high elevations (above 7,500 feet). I have had the car for ~7years and have never had this problem. That is, in the past, i’ve been able to drive it up to 9,300 feet with no problem. Could this be vapor lock? If so, why would vapor lock all of sudden start happening? If not vapor lock, what could it be? Thanks for any comments. Dave

Not likely vapor lock. Does it have fuel injection? It could be a weak fuel pump.

Have someone test the Manifold Absolute Pressure sensor for proper operation.

The computer takes the signal from this sensor and determines when the fuel mixture should be enrichened and the when spark advance should occur. This sensor also informs the computer if there are changes in elevation so the computer can make adjustments for those changes.


1988 Trooper may have had a Carb. I think the 2.8l V6 had a Carb…and the 4-cylinder had fuel-injection.

My fuel injected 2002 Sienna always performed perfectly coming over the mountains from Mexico City to Puebla and I think my handheld barometer put us at like 11,000 feet, I can’t remember for sure.

I do remember many years ago with standard carb motors reading one had to reset the carb at higher altitudes.

The OP didn’t mention how hot it was when the problem occurred. I would suspect the fuel pump might not be delivering the fuel with enough pressure. Vapor lock is more likely in fuel lines with less pressure.