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Old 07-27-2008, 08:16 AM
 
Location: The 719
8,087 posts, read 13,036,887 times
Reputation: 9480
Why don't you take it to Ryan or somewhere and see if it needs a tune-up. After hearing what Sunsprit said, it has me wondering if the altitude makes that drastic of a difference, so long as you have efi on that vehicle.

I know from their postings that Ryan is a mechanic and Sunsprit is one too.

What I want to know and want to ask here is because it involves altitude and Colorado specifically; Why do the lower elevations of Colorado (Lamar at about 3600 ft above sea level) have the lowest octane rating of petro at 87, but when you come up in altitude, the lowest rating petro offered becomes 85 at some point? Is it because of the altitude itself or is the fuel actually different? I believe it's the former, but I'm only assuming this.

PS: Capepuffin, I was trying to figure out why my vehicles run pretty good here and yours doesn't. I came to one conclusion; our hills out here aren't quite like those huge mountains back east! You do have to use a little gas to get up some hills. It may not seem like much of a hill sometimes, but those steady grades will take a toll on your acceleration.

I've got a 63 Chrysler that I drove back from the PNW and I haven't done anything to it yet. With the 2 bbl carb, I've played with the fuel/air a bit, but it runs fine up here. I've got to step on it to get up this one 6% grade hill here, but she'll do 80 with the ac on all the way up if I'm so inclined.

Last edited by McGowdog; 07-27-2008 at 08:43 AM..
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Old 07-27-2008, 08:48 AM
 
Location: Colorado Springs, Co
52 posts, read 146,828 times
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Quote:
Originally Posted by capepuffin View Post
Ummm Yeah, I know the oxygen has something to do with it. That is why I asked the question "are there any adjustments that can be made to make it run better????"
If you think you are down on power driving around up hear, try racing, it sucks. On a naturally aspirated engine you are always going to loose at least 25~30% of your power @6600' elevation. That turns a spunky 300HP v8 into a barely adequate 210HP, or a 160HP V6 into 112HP. What are you going to do with 112HP? The only way to get your power back is going to be with boost I/E supercharger, or turbocharger. Any type of forced induction(boost) is less affected by altitude, as long as you can maintain boost.
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Old 07-27-2008, 08:52 AM
 
Location: Colorado Springs, CO
2,220 posts, read 3,338,500 times
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A decent rule of thumb for altitude-related power loss for a normally aspirated engine (i.e. no turbo or supercharger) is 3% per thousand feet of density altitude. On a hot day the density altitude is considerably higher (by several thousand feet even) than the actual altitude above sea level.
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Old 07-27-2008, 10:33 AM
 
Location: Upland, California
41 posts, read 128,489 times
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EFI adjsts itself for changes in altitude,temp and barometric pressure, so if your car has EFI, no problem. Those of us with carbs need to lean them out a bit. I had to put an aux. electric fuel pump in my '85 Dodge D-350 to prevent vapor lock at high altitudes, loads and temps. It was recommended by a buddy who did the same thing to his Chevy truck. Works great! Just pressurizing the fuel system a little bit stopped the vapor locking problem.
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Old 07-27-2008, 10:38 AM
 
25 posts, read 61,711 times
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My fiance has a 2001 Svt Cobra Mustang w/20K miles (because it hardly leaves the garage)and his car has no problems at all here. He has got power! Me I feel like an old lady because everyone is passing me even other jeeps! I used to have a lead foot, well I still do but I am not going anywhere! I had a tune up right before I moved out here in October. I am going to get my fiance to read your comments because he knows about turbo chargers and cars in general, I know very little. He was actually a mechanic for GM for 26 years in IL. & CA. Retired now though. He knew that the GM cars actually had adjustments that could be made but was unsure about Jeeps. I called the Jeep dealership back about 2 weeks ago and they said there were no adjustments. I still find that hard to believe.

I Went to Bandimere a couple of weeks ago for the NHRA Nationals and I could feel the pit crews frustration with the altitude! John Force did horrible and when I went to get his autograph, he was so upset that it made me upset too! He rubbed off on me
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Old 07-27-2008, 10:40 AM
 
Location: The 719
8,087 posts, read 13,036,887 times
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Can you tell me more about this leaning out? If I smell what seems to be rich exhaust, do I screw the two adjustments in a bit to let less fuel in and more air?

Sorry if the question is a dumb one for a mechanic, I'm more experienced with electrical/electronics- and not so much automotive.
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Old 07-27-2008, 12:39 PM
 
Location: 80919 Rockrimmon yO!
2,738 posts, read 4,586,682 times
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Well, everyone is correct about EFI capepuffin. There are no adjustments to be made for high altitude. It's all handled automatically by the vehicle's computer and /or manifold absolute pressure, and barometric pressure sensors.

If it's running sluggish, perhaps you have an actual problem, i.e, a fuel pump on it's way out, or restricted exhaust or soemthing.

Mcgowdog, what you want to do is turn the mixture screw OUT, to let more air in and lean out the A/F mixture. Of course this will raise the idle, so you will have to back down the idle adjustment to compensate.

It helps to have a 4 gas analylzer to make these adjustments. Most garages around here have them from when COS had emmissions testing.
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Old 07-27-2008, 03:46 PM
 
Location: Colorado Springs, Co
52 posts, read 146,828 times
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Quote:
Originally Posted by Bob from down south View Post
A decent rule of thumb for altitude-related power loss for a normally aspirated engine (i.e. no turbo or supercharger) is 3% per thousand feet of density altitude. On a hot day the density altitude is considerably higher (by several thousand feet even) than the actual altitude above sea level.
You are right, on a typical summer day hear on the north end of COS 7000' elv the density altitude is close to 11,000' so you could be down over 30% from sea level on a good day. Our dyno correction factor is 31% today.

Quote:
Originally Posted by capepuffin View Post
My fiance has a 2001 Svt Cobra Mustang w/20K miles (because it hardly leaves the garage)and his car has no problems at all here. He has got power! Me I feel like an old lady because everyone is passing me even other jeeps! I used to have a lead foot, well I still do but I am not going anywhere! I had a tune up right before I moved out here in October. I am going to get my fiance to read your comments because he knows about turbo chargers and cars in general, I know very little. He was actually a mechanic for GM for 26 years in IL. & CA. Retired now though. He knew that the GM cars actually had adjustments that could be made but was unsure about Jeeps. I called the Jeep dealership back about 2 weeks ago and they said there were no adjustments. I still find that hard to believe.

I Went to Bandimere a couple of weeks ago for the NHRA Nationals and I could feel the pit crews frustration with the altitude! John Force did horrible and when I went to get his autograph, he was so upset that it made me upset too! He rubbed off on me
Ya, I've been racing up there now for the last few years now, and have adapted But my buddies from california are devastated when there 10.50 cars are stuck in the mid to high 11's here. When was the last time your fuel filter was changed? I can understand the big power loss, but you should still be able to maintain the speed limit or better up most hills around hear.

Quote:
Originally Posted by McGowdog View Post
Can you tell me more about this leaning out? If I smell what seems to be rich exhaust, do I screw the two adjustments in a bit to let less fuel in and more air?

Sorry if the question is a dumb one for a mechanic, I'm more experienced with electrical/electronics- and not so much automotive.
Go get yourself a vacuum gauge, and hook it up to a port on the carburetor that has vacuum at idle. Then adjust the screws to the point where you have max vacuum, @ idle in gear, be sure to keep them even. Then try running 15~20% E85 mixed in with your gas. I bet you notice a difference, the E85 mix will lean you out about 5~7%. That should put you close to where you need to be, while raising your octane 4-5 points.
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Old 07-27-2008, 09:05 PM
 
Location: The 719
8,087 posts, read 13,036,887 times
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Wow! A few good things to try. Thanks for the info.

To the OP: are some of these other jeeps you're comparing yours to V8s? I assume your jeep has the 4.7L or 287 CID V8 and not the V6. You wouldn't happen to have 500,000+ miles on it, do you? The altitude will make a little bit of a difference, but you're not racing up to the top of Pikes Peak, are you?
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Old 07-27-2008, 09:11 PM
 
25 posts, read 61,711 times
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No, my Jeep has 70K and it is a 2004, bought it new in 2003. Not racing up to Pike's Peak either. Just driving to Denver once in awhile or around town. I have always maintained it as required to keep my warranty good. So my Jeep has been taken care of. Guess I need to get under the hood and check some stuff out. Thanks for all of your help everyone!
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