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8.1l Cant Tow 7k Lb Trailer :(

TravisAZ

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TravisAZ Enthusiast

TravisAZ

Posted
Posted

I just purchased a 2001 Yukon XL 4x4 with the 8.1 to tow our ~7200lb boat on a tandem axle trailer.

 

I towed the boat home for the first time the other day, and it did not go so well. Pulling a pretty long 6% grade, I was pretty much maxed out around 40mph in what I assume was second gear. There was alot of random noise coming from the eng compartment, but not like what I have heard with a rod knock or something (more random and klanky). My last tow vehicle was a silverado ss, and it would pull a grade like this @ 70mph with the cruise control set.

 

It was around 95-100 degrees out. Both trans and engine temp gauges were around 200. During the worst part of the trip the trans gauge crept up into what I am guessing was the 210 range. There was a point where I had the gas pedal buried in the carpet, going 40mph up this hill, thinking there is no way I make it over without blowing the engine, trans, or both.

 

At this point, I am not sure if the transmission was slipping, or the heat soaked engine was pulling timing or just running bad.

 

Misc details:

- Truck was not loaded down - driver, 1/2 tank of gas.

- I was running 87 octane from Costco.

- The truck seems to run great when not connected to a trailer. Plenty of power, nice firm shifts, etc. the only thing I do notice is some ping at high rpm right when it tries to shift in DRIVE at WOT.

- I assume the truck had the stock 195 thermostat in it at the time, I replaced with a 180 degree today, don't notice a difference in driveability.

- truck has 110k on it, and I have owned it about a week

- Truck has fresh 10w-30 mobil one

- Trans fluid looks 'ok' but not great. after this adventure, I drained 4 quarts through the pan, and replaced. The stuff that came out will not allow light through in a 12 ounce h2o bottle.

- PCM has no codes.

- TOW/HAul button does nothing, most of the towing was done by manually putting the truck in '3'.

 

Looking for things to check - not sure where to start.

 

Thanks!

jro909 Senior Enthusiast

jro909

Posted
Posted

umm my 5.3 can tow 7k, it would be screaming like a banshee but it will do it...are you saying when you push the button it dosen't activate the tow mode? tow mode allows your motor to go into its power band easier and holds gears longer to take the strain off the trans...what gears you got in the rear end? the 8.1 should have zero problems moving 7k so somethings going on

yukon25008.1 Senior Enthusiast

yukon25008.1

Posted
Posted

my 04 yukon 8.1 runs 100% and pulled 8000lbs worth of trailer and 2b stone up a steeper hill, at 110,000 its time for fresh oem delco platinum plugs and good wires (msd) not sure if that model/year has a fuel filter, mine doesnt,

do 1-2 seafoam treatments yourself or find a shop that provides a motorvac service, after that combination it should run like a new truck,

install a new decent brand filter, and clean your maf & throttle body..new coolant wouldnt be a bad idea, im also doing a 180 stat but has to be tuned for it. which gets to mynext point to email justin from (blackbear) andmention your troubles, after you do some tune-up, he will be able to improve things dramatically.

Im getting an in person tune july 17th in buffalo. He sqeezed me in..cant wait

please let us know

Also once i removed the oem muffler and heard and felt a big difference, even if you put two 3" straight pipes in place of the factory muffler. it will be a huge help

pwall Senior Enthusiast

pwall

Posted
Posted

In regards to tow/haul mode doing nothing, when the button is pressed, does the tow/haul light on the dash light up?

If not, then it's not working. One of the wires in the shift level has broken (the orange wire most likely), it's a fairly common problem.

Do a search on this site....plenty of posts regarding that.

Stevens03 Senior Enthusiast

Stevens03

Posted
Posted

There's something wrong... 7000 lbs shouldn't have been an issue for the 8.1 :lol:

 

I'd look at full tune up, fuel filter, clean MAF sensor.. and see how it does from there.

tunseeker1 Enthusiast

tunseeker1

Posted
Posted

Ok I see things different then a lot of people here I guess.

 

It sounds like you just got the truck used and that changes things for me. You don't know what kinds of mods the old owner did.

 

Here is how I would start.

 

Run down the fuel as far as possible then fill with 94 octane. The truck might have a tune you don't know about.

 

Look into the emissions system. Cats,O2 sensor and exhaust. Might need normal service.

 

Change all the fluids. Oil,Tranny,transfer case and diffs. Only way to know the history is to make it yourself.

 

Do a tune-up. Again the only way to know the history is to do it yourself.

TravisAZ Enthusiast

TravisAZ

Posted
  • Author
Posted
Is the truck stock? Stock tires and rim sizes ? Mods?

 

Truck is stock to the best of my knowledge - def the stock CAI, stock tire size, etc.

 

I agree there is alot of work to do to get a baseline on the truck:

 

- Plugs

- Wires

- Cats

- O2 sensors

- Fuel Filter (previous owner claims to have had the fuel pump replaced, cant imagine they wouldn't do the filter @ the same time, but Ill check it)

- Clean Maf

- Clean TB

 

The question is that the truck didn't throw any codes, so which of these would be most likely to cause poor performance, and not throw a code?

 

ALso - about the tow-haul button, yes I am saying I do NOT get a light on the dash when I press the tow/haul. Im sure your right about the wires, PWall, I will check it out before I tow again...

tylerjenkins92@aol.com Senior Enthusiast

[email protected]

Posted
Posted
Is the truck stock? Stock tires and rim sizes ? Mods?

 

Truck is stock to the best of my knowledge - def the stock CAI, stock tire size, etc.

 

I agree there is alot of work to do to get a baseline on the truck:

 

- Plugs

- Wires

- Cats

- O2 sensors

- Fuel Filter (previous owner claims to have had the fuel pump replaced, cant imagine they wouldn't do the filter @ the same time, but Ill check it)

- Clean Maf

- Clean TB

 

The question is that the truck didn't throw any codes, so which of these would be most likely to cause poor performance, and not throw a code?

 

ALso - about the tow-haul button, yes I am saying I do NOT get a light on the dash when I press the tow/haul. Im sure your right about the wires, PWall, I will check it out before I tow again...

 

 

Let me know if you got my message, it didn't show me you got it.

alaska511 Senior Enthusiast

alaska511

Posted
Posted
I would start by changing fuel filter

checking the fuel pressure regulator

fuel pump

converters

I,m guessing a fuel delivery problem

 

 

Agreed.

 

My 8.1 weighing 12,000 with a camper in the back AND towing a 5000 pound boat/trailer would come up long steep grades at 80 easily. Change your fuel filter.

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