Lose Power at High Altitudes

[Guest lonestarpathfinder]

I have a '96 Pathfinder SE that occasionally loses power at high altitudes, while driving in the mountains (I press the gas, but the car will occasionally lose speed). No dashboard indicator lights turn on when this happens.

 

This problem does not occur at lower altitude levels. I had the fuel filter, fuel pump, and air filter replaced a few months ago, but this problem still occurs.

 

Has anyone heard of this problem before, and if so, is there anything I can do about it?

 

Thanks...

[mudfinder]

yeah, i experienced this problem about a year ago when i went up to Big Bear, Ca. my path really lagged up there. but i think it's normal. my cousin has a 4runner and he experience the same thing. so i'm pretty sure it's the altitude. when i got back down. it was back to normal.

[88pathoffroad]

Mine does that too, generally above 2500 feet or so. There's no altitude compensation system on these things, I swear. Makes me wish I could manually adjust the FI map so it'd run right, heh.

[Boris]

Every internal combustion engine will suffer at altitude because there is less air for it to stuff into the cylinders.

Is your power loss all through the rev range or do you develope a flat spot?

 

If it's all over than not to worry as it's normal and there isn't much that can be done about it. A turbo is the best way to compensate as it crams the air in but that can be costly.

[Guest lonestarpathfinder]

It occured when I was driving for a while in 4th gear (5 speed manual transmission), after going up and down a few hills for a while (mostly up though, to about 7000 feet).

 

Would occasionally opening the gas tank cap help alleviate things when I'm up there? Also, if I'm in high altitude and it does happen again, shoud I just keep going, and just accelerate more, or should I pull over and wait a while with the engine turned off?

[keithb7]

The amount of power your engine can produce is severely effected by the lack of fuel being delivered to it. When I mean fuel I mean oxygen. The little explosion inside your engine, every time the spark plug fires, needs gasoline, air, compression and an ignition source. Alter one of those needs and power performance will change. There is less oxygen in the air as you climb in elevation. People who climb Mt. Everest can attest to this. I am been out hiking at elevations of close to 10,000 ft. It is exhuasting, feels like someone tied a ball and chain to one of your legs.

 

It's ok to keep driving, pulling over and stopping won't make much difference. A K&N filter might help a little as it allows more air into the engine at all times. I have experienced this several times while out on my dirtbike as well. When you get back down to sea level it feels like you just gained way more H.P.

 

Opening the gas cap won't do much. The fuel cap is pressure regulated.

 

Keith

[Guest lonestarpathfinder]

I talked to a mechanic and he said it may be a bad MAF (Mass Air Flow) sensor.. He is going to charge me $135 to run a diagnositc to check.. But no dashboard indicator lights came on when this problem occurred, so nothing would turn up if he runs a diagnostic check right?

[88pathoffroad]

$135 for a diagnostic is extremely excessive. All he has to do is run the ECU error codes with an OBDIII scanner. Five minutes worth of work for $135? I don't think so.

 

You can get the same service free at AutoZone or Schucks/CSK Auto, try that first. Ask if you can get a free scan of the ECU codes at the counter. That's how cheap it is and how much you're getting ripped off if you pay that much for diagnostics...

[Guest Gandalf]

What kind of altitude are we talking about? Mine starts to slow down noticably much above 12,000', but so do I. I suspect the MAF sensor could be bad and I would check the O2 sensor too. Basically you have a combustion problem -- either not enough or too much of something. How's your gas mileage?