Having Trouble Starting at Altitude

I’ve got a 99 Ford Ranger that works fine at sea level, but when I drive up in to the mountains (about 9000 feet) it’s recently been having trouble starting. The starter cranks, but the engine doesn’t start. It’s not vapor lock, I tried opening the fuel cap and that didn’t help. It does start if I pump the gas pedal.

I’m wondering if this could be a problem with the new fuel injectors which I just had installed. This never happened on numerous trips up to altitude prior to those new injectors being installed.

Any advice would be appreciated.


First, understand this. At higher altitudes, the air fuel mixture needs to be leaned.

The old injectors probably didn’t get quite as much fuel to atomize and go into the cylinders. Any chance these are performance injectors?

Pumping does nothing on a fuel injected vehicle that holding the pedal down doesn’t do better.

It may not be able to lean the mixture enough without the throttle plate open during starting. If you had a ECM capture tool, it would be nice to see what it THINKS the manifold air pressure is. MAP sensor may be fooling it into thinking it is at a lower altitude.

Until then, try holding the pedal down during high altitude starts. Probably just slightly richer mixture with your new injectors at startup before it adjusts mixture using O2 sensor readings.

Also check fuel pressure readings at the rail, at altitude, and see if they are on the high side. Not so critical at sea level, but much more critical almost 2 miles up with the air only 71% as dense.

There might be some restriction in the air intake tract. You can improve that by using a Throttle Body Cleaner to clean out the idle air control valve passages, throttle bore and throttle plate.