ctopher

Anybody had this happen before. I drove my 2005 RL on trail ridge road in Rocky Mountain National Park a few weeks ago and at 12,000 foot elevation mark going about 20 miles per hour it started to slow, sputter and as I pressed the accelerator down more it jerked and then stalled (of course traffic couldn't get around me since it was one of the narrowest parts of that road). Just before it stalled I flipped it to manual shift and the displayed said it was in first gear. I wanted to make sure that it wasn't stalling because it wasn't stuck in a higher gear climbing up the mountain. All the electrical seemed fine when it stalled. I turned it completely off for 30 seconds and it started back up and it sputtered a bit while driving it to a parking lot about 100 yards away. I let it sit for 15 minutes, checked fluids, then drove it back down the mountain and on peak to peak highway very agressively and nothing seemed wrong. When I brought it into the shop the next week for an A1 service I told them about it and he said they wouldn't be able to figure much out since I didn't see any errors displayed. When I picked it up they didn't find anything. Just curious if anyone else has seen this. Someone mentioned to me that most electronics in the cars like the RL are only tested to 10,000 feet above sea level. I have no idea if that is true or what it would mean in terms of what happened to me.

topher

mrdeeno

doubt it's the electronics...probably vapor lock.

Rexorg

Sounds like your RL had attitude sickness due to lack of oxygen and probably the grade of gas you were using, and how full your tank was. Also at 12,000 feet the temperature also has to be factored in. I would guess your RL's computer just could not keep up with all the extreme parameters you were throwing at it and decided to go into safe mode.

mrdeeno

It doesn't have anything to do with electronics...it's vapor lock.

The ambient pressure is lower at higher altitudes. At lower ambient pressures, liquids boil (turn to vapor) much easier. At extremely high altitudes, the ambiet pressure is much much much lower, so liquids (such as gasoline) turn to vapor much much much easier.

At these low ambient pressures, the fuel pump has enough negative pressure (suction) to vaporize the gasoline, leading to starvation of fuel to the engine and therefore stalling.

1HOT NSX

I've had mine up to 11,000 feet with no signs of air sickness. I do lose 5th gear at the top of the mountain. For some reason it refuses to shift into 5th gear with the paddles when I get up to altitude after a spirited run on a curvy road. Everything looks normal including the engine temperature As soon as I start the downhill run 5th gear comes back. If the 12000 ft ceiling is true, I feel for the poor Bolivian RL owners

JPritch

I know with your typical light airplanes, you have to lean the fuel/air mixture at altitude, due to the decreased density of the air which can cause an excessively rich mixture.

Not sure if car engines even work the same way.

dramsey

Modern port fuel injection systems run at high pressures, from 40psi on up to hundreds of PSI. I've heard of some cases of vapor lock in cars that were sitting (engine off) for a long time, where residual pressure in the system declined, but never while a car was running.

THat said, I've no idea what the problem with the car was.

mrdeeno

I didn't mentnion anything about the fuel injection...that's the fuel AFTER the fuel pump, not before.

the fuel pump has to SUCK fuel before it can pump it, which means that there is negative pressure on the inlet side of the pump, which is where the vapor lock occurs. If the gas becomes a vapor before it even reaches the fuel injectors, you're SOL.

dramsey

I don't see how gasoline could become vapor on the back side of the pump. In the engine compartment, there's lots of heat to help the process; between the gas tank and the engine, not so much. Also, aren't the fuel pumps integrated into the gas tanks on most modern cars? Where would the vapor lock occur?

1HOT NSX

My guess is that vapor lock has nothing to do with it - not in the tank, pump, lines, injectors, etc. The first possibility and a remote one at that: the intake air sensor is not capable of dealing with readings at 12K feet, confusing the electronics that control the injection system. A more likely possibility is a failure at altitude by this one car only, caused by a malfunctioning air intake sensor.

dramsey

Light airplanes have very primitive engines compared to modern cars, without most of the computer controls we take for granted. Also, they typically have a MUCH longer operational life than a car; 20 year old light planes are the norm, and 50+ years isn't that unusual.

While many owners upgrade avionics (nav systems, etc.) engine upgrades are almost unheard of. Thus most light planes have no computer controls at all on the engine, and many still use carburetors! So the pilot has to do some things (like mixture adjustment) manually, while our cars handle it automatically.

In this case, the car's "mass airflow sensor" knows exactly how much air is getting into the engine and tells the engine control computer how much fuel is required.

ctopher

Thank you all for the responses. A couple more things to mention. With the same care I've been in the exact same location a year ago to the same month with no problems. Also, I always but the highest octane gas in at the 2-3 same gas stations I've used the passed 1.5 years here in Colorado. And a third point. It was very hot down at 5,000 feet above sea level where I had traveled up from (100 far.) and when I got to 12K the outside temp. as reported on the dash was 81 .. which is much warmer then it ever has been when I'm up there.

Thanks again for the responses. Car is still running great since then .. and I'm still loving that I own it.

topher