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Unread 11-11-2010, 09:44 AM   #31
mthomp83
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I entered at Amicalola State Falls Entrance. Once you get to the visitors center, there is a road on your left that goes up a hill. This road leads up to camp sites and cottages and have a very steep grade. These roads are where I lost the most power.

Do you know where I'm talking about?

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Unread 11-11-2010, 10:08 AM   #32
Ajaxxx
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Originally Posted by mthomp83 View Post
thank you for the response, the hill grades were about 20-25% so it was pretty steep, not much wind though
My other vehicle is a 2009 F150 FX4 with 5.4L, and when running 20% grade it sucks like a dog too. Shifts down into 4th (6spd auto) and doesn't want to get out of its tracks at 55mph. Add elevation and less hp, I'm sure it felt like the Jeep wanted to come to a standstill...

IowaAndy
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Unread 11-11-2010, 10:11 AM   #33
mthomp83
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Originally Posted by Ajaxxx View Post
My other vehicle is a 2009 F150 FX4 with 5.4L, and when running 20% grade it sucks like a dog too. Shifts down into 4th (6spd auto) and doesn't want to get out of its tracks at 55mph. Add elevation and less hp, I'm sure it felt like the Jeep wanted to come to a standstill...

IowaAndy
that sucks, but its actually very great to hear that, thanks for the comparison, it really makes me feel better about it now

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Unread 11-11-2010, 10:56 AM   #34
paul84043
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Okay, here's a theory for you....maybe vehicles that live and breathe in the lower altitudes are much more sensitive to the changes, kind of like when you're SCUBA diving the first three atmospheres are the most critical and after that, the differences become much smaller. (orders of magnitude)
So, if my vehicle has tuned itself to run at 4500ft, going to 8000 isn't the same as taking a vehicle from 1000 ft, to 2000 ft, there's a huge difference in the pressure differential.

Just a thought?
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Unread 11-11-2010, 11:10 AM   #35
jpacosta
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mthomp havnet been there but have traveled through alot of the forest. this was a gravel FS Road correct? were you running 2wd or wat?
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Unread 11-11-2010, 04:52 PM   #36
1222
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Quote:
Originally Posted by paul84043 View Post
Okay, here's a theory for you....maybe vehicles that live and breathe in the lower altitudes are much more sensitive to the changes, kind of like when you're SCUBA diving the first three atmospheres are the most critical and after that, the differences become much smaller. (orders of magnitude)
So, if my vehicle has tuned itself to run at 4500ft, going to 8000 isn't the same as taking a vehicle from 1000 ft, to 2000 ft, there's a huge difference in the pressure differential.

Just a thought?
Nice theory but modern day fuel injection will compensate for the altitude changes.
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Unread 11-23-2010, 05:18 PM   #37
mikeinminn
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Fuel injection doesn't compensate for elevation at all. All the system does is mix the appropriate amount of fuel for the air density/volume available. That is why you'll get pretty good mileage in Colorado. With less air there is less fuel....and less power. Turbos are less affected by altitude because the turbo rams the air into the intake and creates its own "atmosphere". What Paul wrote is in part true but not for the reason he inferred. If memory serves, 80% or so of earth's oxygen is in the lowest 14,000 ft above sea level. What that means is as we go straight up the air thins much more rapidly than you might expect. Engine computers respond by reducing the flow of fuel and what was once a dog is now a tortoise. One other issue is the auto tranny. As a huge viscous coupling, it absorbs a load of horsepressure that our Jeeps just can't spare. I have the same issue so I'm saving for a supercharger.
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Unread 11-23-2010, 06:16 PM   #38
Charles
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Originally Posted by mikeinminn View Post
Fuel injection doesn't compensate for elevation at all. All the system does is mix the appropriate amount of fuel for the air density/volume available.
That's EXACTLY how fuel injection compensates for altitude. There is less air at altitude so when you go higher fuel injection pulls fuel. If it were carbureted would run rich.

EDIT: Oh, and turbo charged cars loose the exact same amount of power at altitude as other vehicles. If a NA car loses 10% of it's power at altitude a FI car loses 10% too. The turbo does NOT spin faster at altitude.
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Unread 11-23-2010, 07:11 PM   #39
mikeinminn
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I meant that a vehicle can't tell if it is going up in elevation or sitting in the center of a hurricane....all it does is adjust for air density. It doesn't compensate without the accompanying loss in power. My point was that the vehicle doesn't "know" what elevation it sits at. Obviously only a detail as long as its understood that the "compensation" that FI does is done at the expense of power....maybe part of the reason why the OP was experiencing power loss.

Your explanation regarding turbos makes sense to me. I've been told the opposite by people who should know so many times that I didn't stop to question it.
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Unread 11-23-2010, 07:14 PM   #40
babiehughie
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Sounds like a couple of pages have made a left turn. Did you all forget about BLD and ESP? Both rob power when traction goes south. 20-25% grade could set them off. What range was your transfer case in? If you were traveling less that 20-25 mph, then stop and shift into 4lo. This will quadruple (Rubi 4:1 ratio) your available torque, and you won't have such a dog. You bought 4WD with a lo range transfer case, now use it!
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Unread 11-23-2010, 07:27 PM   #41
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It has nothing to do with fuel injection. It is all about atmospheric pressure and the O2 ratio at a given altitude. You can only pump so much air through through the throttle body unless you are running a turbo/supercharger setup to compensate. At 18k feet a normally aspirated engine only has 1/2 the available atmospheric pressure available to suck from...the O2 is diluted and fuel maps reading your O2 sensors will only provide half the gas to solve a correct air fuel ratio. 14pis at sea level, 8 psi at 18k. At 18k the jk would put out 90hp at the crank, probably more like 70 to the wheels.
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Unread 11-23-2010, 08:17 PM   #42
Charles
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Originally Posted by mikeinminn View Post
I meant that a vehicle can't tell if it is going up in elevation or sitting in the center of a hurricane....all it does is adjust for air density. It doesn't compensate without the accompanying loss in power. My point was that the vehicle doesn't "know" what elevation it sits at. Obviously only a detail as long as its understood that the "compensation" that FI does is done at the expense of power....maybe part of the reason why the OP was experiencing power loss.

Your explanation regarding turbos makes sense to me. I've been told the opposite by people who should know so many times that I didn't stop to question it.
So, whatever you want to call it, the fuel injection compensates for altitude because the air is less dense.
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Unread 11-23-2010, 09:01 PM   #43
mikeinminn
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Yes...so long as keeping the engine running smoothly is all you're after. But someone reading this thread may have thought that the FI system was keeping the engine power as it was when they read "compensates",eh?
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Unread 11-24-2010, 10:41 AM   #44
piratius
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Originally Posted by cbloyer81 View Post
EDIT: Oh, and turbo charged cars loose the exact same amount of power at altitude as other vehicles. If a NA car loses 10% of it's power at altitude a FI car loses 10% too. The turbo does NOT spin faster at altitude.
Actually, you're wrong here. Turbochargers use a wastegate to keep maximum boost pressures constant. A wastegate set at 12psi will produce 12psi boost at sea level, and 12psi boost at 10,000ft elevation. The "speed" the turbo is spinning will change depending on altitude, and doesn't matter to the wastegate, which is actuated by springs and manifold/turbine pressure, not by a set rpm for the turbocharger.

I've only built a few naturally aspirated cars into turbo cars

:teacher:
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Unread 11-24-2010, 11:54 AM   #45
paul84043
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Originally Posted by 1222 View Post
Nice theory but modern day fuel injection will compensate for the altitude changes.
Well, the point I was kind of trying to make is that the vehicle will adjust itself, but it will do it slowly, it's not immediate, it could take several hundred miles to compensate for a great change in altitude...

That's all...
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