:help:I recently returned from Colorado where I had problems towing at 7000 ft. and above. I am towing a close to Max combo weight at about 21,000 lbs. with my 05 GMC, a LLY engine and Allison Trany. I have towed this trailer for well over 10,000 miles up and down the East coast and have had no problem at 4000 ft. or less, but when I got stopped at about 8000 ft on a Mtn. because of road work I almost could not get the rig rolling again. It moved at a snails pace for about 25 or 30 Yds. untill it went into 2nd. gear. After shifting into 2nd. it started to pick up speed but realy struggled. It continued to give me trouble starting out from a dead start until I got back down to about 4000 ft. I took it to John Elroy GMC Near Golden Co. and they checked it out on their computer but it did not show any codes so they could not help me. I am wondering if this type of performance is normal at that alditude, and if so what can I do to correct it before my trip back to Colorado next year. Any advice Greatly Appreciated.

I have never had that problem. I've never been at 21k gross, but do run 17k gross.

Hows your fuel filter? We has some similar problems in CO last year on our way to Elk Camp.We apparently got some bad fuel and when going on any incline with our 22' trailer w/ 4wheelers it just wouldn't go.Once we changed it ,it would fly.

The GM dealer checked everything including the fuel vacum and said it was all normal, however I will change my filter as it is due. Problem is I do not have any higher than 3500 ft around here to see if it is pulling correctly. It only seemed to be powerless in 1st. gear before the turbo kicked in. Maybe I need a power chip to correct it but I would like to see if anyone else is having the same problem and what they have done to correct it.

When you start up from a standstill, your turbo has not spooled up yet (nor will it until it gets more fuel, and that might be delayed by the MAF sensor waiting for more airflow - smoke issue). That being the case, your engine becomes Naturally Aspirated, and available HP is reduced by approimately 4% per 1000'.The low stall speed of the Torque Coverter compounds the problem, limiting the engine RPM. A power enhancer that by-passes the MAF (such as Edge) helped me with a similar problem.

Tom,
Thanks for the info. Does the edge boost 1st gear performance considerbly with out harming the Tranny?

I do not have that problem once the turbo starts spoolin up, but like horse trainer says, naturally aspirated looses power. I personally would not trust John Elways mechanics to even wash my truck.

when i pull around 14000lbs at about 7000' the truck has a hard time starting. once moving it has tons of power.

The Edge did help some, and is good cost wise, but I think the real solution lies in a different Torque Converter, which I have yet to try ($$$$$$$)>

Well , By What Several Have Said It Seems To Be A Problem That Comes From The Computers Normal Programing That Cuts Power In First Gear To Save The Tranny. This Doesn't Seem To Cause Problems Until You Get To 7000 Ft. With A Large Load. It Then Seems To Reason That The Only Way Of Overcoming This Problem Is To Put A Chip In It That Will Allow More Horsepower In First In Turn Allowing The Rig To Get Into Second Gear A Lot Faster. All I Know Is That I Can't Live With The Unbeliveable Lack Of Power It Is Delivering In First Gear & Doubt If Any Gm Tech. Will Be Able To Help Me. This Is The Only Time I Have Ever Been Imbarrised By My Duramax. Any Other Comments On This Matter Will Be Appreciated.

Hey guys, Just got hooked up on this forum, I was just trying to figure out a similiar issue with my Dad's LLY Duramax. We're at 7600ft elevation and that truck won't spin the tires on gravel till it hits 2500 RPM. Dealer has had it, and tightened up some "turbo bands" or something. But I drove it this weekend and was surprised by it's lack o gumption below 2500 rpm. Guess I too will suggest that he change the fuel filter and see what happens. Was also wondering if it had something to do with the, what is it, variable vane turbo? I know it got pretty hot at one point pulling a 35' fifth wheel on a long 10% grade in Alaska. Could that have damaged the variability in the Turbo?

I would try a small tow tune. High altitude certainly robs power, even in turbo engines. Stick to about a 50-65rwhp tune. They dramatically improve spool up time, and usually will give you slightly better MPG in the mountains.

You all crack me up. I live at 10,200 feet. I have NO clue of what my truck would do at sea level (or for that matter below 5000 feet). Seems fine to me:bigglasse

You all crack me up. I live at 10,200 feet. I have NO clue of what my truck would do at sea level (or for that matter below 5000 feet). Seems fine to me:bigglasse

Can I assume you live at/near Leadville CO? ...or possibly Alaska somewhere? ...or out in the wilderness mountains, because I don't know of any locations in the US that are that high... :confused:

Leadville;)

Durabill states "but when I got stopped at about 8000 ft on a Mtn. because of road work I almost could not get the rig rolling again. It moved at a snails pace for about 25 or 30 Yds. untill it went into 2nd. gear. After shifting into 2nd. it started to pick up speed but realy struggled. It continued to give me trouble starting out from a dead start until I got back down to about 4000 ft."

By now I would have thought everyone on this forum would have been following the overheating threads, especially those that tow heavy. :rolleyes: Your experience sounds like the classic "heatsoak" that happens when you stop these trucks while towing heavy, the engine compartment gets saturated with super hot air, you hit the go-pedal and it doesn't want to move. Compound that even more at higher altitude with less available oxygen to burn.

These engines are not designed to ingest that much hot air, once you are moving and inlet air temps come down the truck regains its power. Plenty of intel in the LLY engine forum on this phenom. Oh, there are some fixes in the works that will help.

Hope this helps. JJ :)

Hay jj , Thanks for the Info. on the heat sink problem. That makes a lot of sense. I realy wish that the Service people would be up on these things but I guess that would be too much to ask. It seems like I learn more on this web site than they even want to know. I have ordered a Edge with Monitor & hope that will help some. I will be taking a trip into N.C from Pa. and will hit some 6 & 7% grades, so when I return I will report on how the Edge does.
Thanks for everyones help.

By now I would have thought everyone on this forum would have been following the overheating threads, especially those that tow heavy. :rolleyes: Your experience sounds like the classic "heatsoak" that happens when you stop these trucks while towing heavy, the engine compartment gets saturated with super hot air, you hit the go-pedal and it doesn't want to move. Compound that even more at higher altitude with less available oxygen to burn.



JJ hit that one out of the park. I have tested this exact scenario. It is the toughest stress test you will ever perform. Never park pointed uphill, at altitude, unless planning to cool the vehicle for a few hours. It takes 10 secs for underhood temps to rise 100 degrees. The IAT rises to over 250 degrees, up to 180 degrees over ambient. Getting this turbo to create 20 lbs of boost using that air at altitude is a lesson in thermodynamics. It has no efficiency. The resultant turbo-out stream to the CAC is well over 600 degrees, and the post-CAC intake combustion air is well into the 250+ range. The motor never was intended for combustion timing using this hot air. You may even feel a "miss" or "backfire". If you do get it moving a bit, the air intake quickly gets cooler and CAC function is also restored with air flow (movement). Power comes back.

Cure: Cold Air intake. A real one.

How about drawing cool air from the outside of the hood? One of the other discussions had a thing about installing an older air box to draw air from the wheelwell????

Durabill, the same thing happened to me on Monarch Pass last summer after I stopped 1/2 way up the west side of the mountain to cool the engine down!
I have been modifying my truck (stack seal,radiator shrouds,cold air intake,3"air dam,JK's splash shield mod.) to help eliminate the overheating/heatsoak conditions.
These mod's have been created, developed, & tested by a number of forum members.
I have not had the chance to hit Monark Pass at 85* again, but I have noticed cooler temps and better power with these mod's towing in the flatlands of Kansas.
We will find out next summer.

Big Daddy, Thanks for your input on that problem. The Tech. at John Elroy GMC Had me thinking it was supposed to run that way. I have started Mods. on mine also but wont be back out west till next spring.
I am taking a trip to N.C. this Wed. for the first tryout of the Edge Juce with ***.
I just installed it yesterday and it is running well. I anxious to try it with the 5TH wheel on the W.V. and Va. Mtns. They are nice long grinds at about 6 or 7 % but only go to about 4,000 ft.
I will report back on it when I return.:grd:

Durabill,

Your towing heavy. Suggest E/J power Level 1, defuel all shifts, smoke setting to "carb". Have a safe trip. JJ :)