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Difference between high altitude and low altitude diesels?

Discussion in '1982-Present GM Diesel' started by Danno, Oct 13, 2001.

  1. Danno

    Danno 1/2 ton status

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    While crawling around under the hood today, I stopped for a break and read that emissions sticker on top of the radiator. It said at the bottom that my truck was "for low altitude operation".

    What altitude would GM consider "low", and what might the differences be between a low and high altitude diesel engine setup? I know there are different injection pumps, but what else?

    1984 K5 Blazer 4x4 Silverado
    6.2L diesel, 700R4, 3.42 gears, 31x10.5" tires
     
  2. DieselDan

    DieselDan 1/2 ton status

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    I have no idea what GM considers low or high altitude, maybe someone from Coldorado could tell ya. Yes, there are differences in the pump calibrations between DS-2 (mechanical) pumps. I would assume that a low altitude pump would have the delivery turned alittle higher as there is more air (desnity) available. Diesels burn up if they run too rich (exhaust temp gets too high). They always run some air/fuel ratio lean (constantly changes depending on RPM/load). Simplified greatly.

    Real trucks don't have spark plugs!
     
  3. Danno

    Danno 1/2 ton status

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    So, I should probably think about investing in a different injection pump to keep my diesel from running too rich all the time?

    Argh. Remanufactured injection pumps look expensive. NAPA Online lists low and high altitude remanufactured DS-2 pumps for $431 (with a pretty good core return).

    1984 K5 Blazer 4x4 Silverado
    6.2L diesel, 700R4, 3.42 gears, 31x10.5" tires
     
  4. chevyracing

    chevyracing 1/2 ton status

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    This will probably get stix and stones thrown at me but here it is anyway. The air fuel ratio, rail pressure, and timing will be slightly different. If the engine was turbo-charged there would not be any difference because there is not a road in america high enough to affect a turbo charged engine. I have seen arguements on both sides of that story and I tend to edge toward the side I stated. A turbo charged engine has a metered amount of air going through it that will draw what it needs depending on demand as long as it is working correctly. If a boost sensor or maf sensor, transfer pump or the waste gate are not working correctly altitude will affect them then. Most of the new diesels have a waste gate type turbo that bypasses eccess (<----spelling error) boost. The keyword is excess(<----probably another spelling error) boost.
    Anyway, this is off the subject you inquired about and I don't even know why I am saying this, must be the two pots of coffee.

    John

    Like to go sloppin' 'round in da mud in a rapid fashion....=) [​IMG]
     
  5. Tybee

    Tybee 1/2 ton status

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    Ill look and see what mine says.


    1984 GMC Jimmy 379 diesel, 700R4, 3.73s, 31x10.50 x 15
     
  6. Tybee

    Tybee 1/2 ton status

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    Just checked mine says high altitude on it, on the sticker it had throttle position gage. That might be one difference whatever its gaged to.

    1984 GMC Jimmy 379 diesel, 700R4, 3.73s, 31x10.50 x 15
     
  7. DieselDan

    DieselDan 1/2 ton status

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    Well, I would really only be concerned if you tow some wight around from time to time. The factory usually considers the worst case scenario. Still concerned? Buy an exhaust pyrometer, the first step in diesel high performance and watch those long hills! If the temps are getting too hot (1050 - 1200 depending on sensor location) you can reduce to total fuel delivery amount.

    As far as MAF, fuel rail pressure, and electronic waste gates - wrong site buddy! He is right about one thing though, turbos (including turbo-diesels) work extra well at high altitudes. The lower air pressure allows the exhaust to exit easier, and compensate (with boost) for the less air molecules (boy, I didn't want to use that word) available at altitude. Watch the Pike's Peak races, the turbo cars are still cranking hard at the end/top.

    Real trucks don't have spark plugs!
     
  8. Danno

    Danno 1/2 ton status

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    Interesting.

    I'm going to have to meet someone with a "high altitude" diesel and compare engines sometime... See if there's anything obvious (size of EGR?).

    So, who wants to gather for a Denver Diesel Jamboree? Hehehehehhe!

    1984 K5 Blazer 4x4 Silverado
    6.2L diesel, 700R4, 3.42 gears, 31x10.5" tires
     
  9. chevyracing

    chevyracing 1/2 ton status

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    I know it is the wrong site for all that. I have a gas engine (383 Stroker) in my 72 but I figured I would come and visit the Diesel dirt diggers and share my wealth of knowledge........Just wanted to fit in, that's all =) LOL.
    Have a good one.

    John <------!!!!!POOF!!! Returns to propper place on site

    Like to go sloppin' 'round in da mud in a rapid fashion....=) [​IMG]
     
  10. pcorssmit

    pcorssmit 1/2 ton status

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    <blockquote><font class="small">In reply to:</font><hr>

    If the engine was turbo-charged there would not be any difference because there is not a road in america high enough to affect a turbo charged engine.

    <hr></blockquote>

    Turbo Diesels ARE affected by altitude. No, they don't loose as much power as NA motors, but they are still affected. A TD setup for sea level will smoke much worse here (Colorado). When I put a power kit in mine, I had to adjust the star wheel on the AFC housing to compensate for the altitude, to avoid the freight train effect. Try going camping with somebody with a power stroke at high altitude when its cold out, they often have a hard time starting. There was a pretty long post about this on the TDR a few months ago, and everyone reported similar results when visiting high elevations (the post was about Colorado driving).

    Pete

    '83 K5, 350 TBI (ex 6.2), 700R4, NP208, Dana 60/14 bolt, 4.56s, Detroits, 3" lift, 15-39.5x15 TSLs
    '97 Dodge 2500 4x4 CC LB Sport, Cummins 5 spd
     
  11. 6 2 Carl

    6 2 Carl Newbie

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    The 6.2L diesels have a Housing Pressure Altitude Advance (HPAA) system. The way this system works, depends whether or not it is a low or high altitude truck. On the low altitude trucks (NA5) the timing gets advanced 2 degrees when at a altitude of 4000 ft or higher. This helps the engine deal with the thinner air.

    On a high altitude truck the timing gets retarded 2 degrees at altitudes of 4000ft or less.

    This system is explained really well in the Haynes Diesel Repair Manual.
     
  12. chevyracing

    chevyracing 1/2 ton status

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    I pull a 30 foot fifth wheel and a 20 foot boat behind that over loveland pass right through the Eisenhaur (&lt;----spelling) Tunnel with my 99 one ton dually Dodge with a Cummins/ auto tranny in it at the speed limit. The camper weighs around 12,000 pounds and the boat weighs around 3500 lbs. My pyrometer gets to about 900 degrees and my boost gauge goes all the way up between the yellow and green marks just like it did going up highway 71 over the Ozarks in Arkansas. If altitude affected it I darn sure could not tell. As far as some diesels having a hard time starting in the altitude, if they aren't running, the turbo is not spinning, (usually.) If the turbo isn't spinning the engine is just getting regular ole air. Don't know about you but when I pull something with my truck I have the engine on.

    John

    Like to go sloppin' 'round in da mud in a rapid fashion....=) [​IMG]

    <a target="_blank" href=http://community.webshots.com/user/chevyracing>http://community.webshots.com/user/chevyracing</a>
     
  13. Danno

    Danno 1/2 ton status

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    Ah cool. I have that book somewhere, I must have missed that when I skimmed through it earlier.

    Now I have something interesting to read this weekend.

    1984 K5 Blazer 4x4 Silverado
    6.2L diesel, 700R4, 3.42 gears, 31x10.5" tires
     
  14. chevyracing

    chevyracing 1/2 ton status

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