2008 Yukon XL Drive train Issues.

[Derick R]

Hello all I'm new to this read forums my entire life when needing help on a issue someone had back in 99. But anyway I have a 2008 Yukon xl 5.3 bought it a few years back quickly realized there was a issue on top of issue. I got screwed and screwed big time. Truck was sold as 168k miles. It was clean nice good looking truck for 4800 bucks. Turns out won't go over 65. We'll we just said screw it and run it for a while until we got our excursion. So now I've been trying to fix it. I need help I've tried refresh at the dealer it sat there for a entire day in a bay with a tech and they couldn't figure it out. So back to the drawing board. Later on tried to trade it in they pulled the carfax trunk our dude swapped the cluster and it was said the last reported mileage was 278k. Well ******. I want to figure out why it will not surpass 65. It has all the gears. Engine has all the power. No limp mode no codes. I have even pulled the cluster and drove it and that didn't change anything. Please help. Thank you. Derick r. 

[swathdiver]

Maybe they set that speed limit in the tune?  It can be done and undone with EFI Live or HP Tuners.

[Derick R]

14 minutes ago, swathdiver said:

Maybe they set that speed limit in the tune?  It can be done and undone with EFI Live or HP Tuners.

I was awaiting this. So first thing I had them try at the dealer was complete reflash and then individual reflash and to also check if there was a governor because our original thought was that it was a company car.

 

Edit: and this is what caused me to explore options and thought it was possible that the scam gauge cluster that was put in to roll the miles back was causing it. 

Edited September 26, 2022 by Derick R

[richard wysong]

Partially clogged cat possibly? Pull an 02 sensor and take it for a ride or check the back pressure. Maybe fuel strainer restricted, put a fuel pressure guage on it and take it for a ride

[Derick R]

3 minutes ago, richard wysong said:

Partially clogged cat possibly? Pull an 02 sensor and take it for a ride or check the back pressure. Maybe fuel strainer restricted, put a fuel pressure guage on it and take it for a ride

I did put a gauge on it to check and went and did a couple runs but it stayed within the ranges that the specs were saying. 50-65 between idle and driving. I haven't check cats but it's really making me think it's electrical of some sort due to how it literally stops and stays at 65 mph and if I go down hill and hit let's say 67. It will not let me have throttle response again until I drop to around 58-60 mph.

 

 

All help is appreciated yall I am a mechanic/fabricator by trade so the more brains the merrier. 

[Derick R]

Also I can take a video of it and post if that will help to show how it acts and reacts to input I've wondered about throttle peddle and or throttle body. 

[swathdiver]

Fuel pressure while running should be 43.5 psi with the LMG and LC9 engines.  Don't know about the LY5 or L76.

 

 

[Derick R]

2 minutes ago, swathdiver said:

Fuel pressure while running should be 43.5 psi with the LMG and LC9 engines.  Don't know about the LY5 or L76.

 

 

Noted but still I don't believe fuel starvation or to much is the issue it literally feels like a srock governor but I can get it to downshift I Rev up but will not surpass 65 

[richard wysong]

yeah that sure sounds like a governor issue. My 98 was set at 100mph and does basicly the same thing but never tried to get it to downshift. I haven't seen what the 04s set at. Maybe some1 who has more experience with tuners can help

[Derick R]

14 minutes ago, richard wysong said:

yeah that sure sounds like a governor issue. My 98 was set at 100mph and does basicly the same thing but never tried to get it to downshift. I haven't seen what the 04s set at. Maybe some1 who has more experience with tuners can help

See that's the thing though there is not tuner (and I don't think there's a tune on it) I've seen 1 other instance where throttle and speed was affected but that was the throttle pedal along with throttle body but I don't want go throwing expensive parts at our nice beater lol but I would like to figure this issue out because it's a interesting one.

[richard wysong]

It should throw a code if it was a throttle problem and wouldn't be speed affected and should limit RPM in neutral I think. I think your theory that it was a fleet vehicle may be correct. I'm gonna go with swathdiver on this and say try an aftermarket tune.  A techII may show/record what is shutting it down as well

[swathdiver]

Despite the dealership flashing the computer, I think you ought to find your local speed shop and have them put their laptop on it.

 

 

[Derick R]

51 minutes ago, swathdiver said:

Despite the dealership flashing the computer, I think you ought to find your local speed shop and have them put their laptop on it.

 

 

Yeah the problem with that is all the immediate Tuners are all import I'd have to travel to find a gm tuner near me. It's alot of ricers/Tuners around here sadly. 

[swathdiver]

3 hours ago, Derick R said:

Yeah the problem with that is all the immediate Tuners are all import I'd have to travel to find a gm tuner near me. It's alot of ricers/Tuners around here sadly. 

If they're using HP Tuners or EFILive! it doesn't matter, all you want them to do is change 65 to 98 or 112 or whatever.  I know some guys up that way, what town are you in?

[Derick R]

1 hour ago, swathdiver said:

If they're using HP Tuners or EFILive! it doesn't matter, all you want them to do is change 65 to 98 or 112 or whatever.  I know some guys up that way, what town are you in?

Toledo area I appreciate all the help I'm just trying to be as detailed as possible to make sure you guys have all the info. 

 

 

Edit: also I've actually called and asked the ones in this area and they all said no they don't have the ability to get into gm but I understand what your saying about the 2 Tuners and having the ability to do so but even the dealership couldn't find any governor they said they even programmed it at 999 to see if that would change it 

Edited September 27, 2022 by Derick R