08 Silverado 4.8 horrible accelration/MPG Stumped ??

[350Rocket]

Torque management at work? IIRC the ECU won't let full power in 1st gear.

Possibly a recalibration of that. Both vehicles are drive by wire but it's more apparent in the 2013. My 05 has it also but maybe it doesn't keep it from full power in first gear. It feels like it gives full power in first gear after it winds up past 3000rpm.

 

[OVERKILL]

Isn't that the point? Spinning a tire on dry pavement means it's going to be spin-fest on any other kind of surface. That sort of thing is hard on spiders, and worse if a spinning tire suddenly grabs. Plus a transmission has a limit to input torque--the allowable torque likely rises as one goes up in gears, but in first gear it's gotta be low to prevent damage, to the trans and/or rear diff.

Now maybe GM was over the top, dunno.

My buddy's work truck that I made a thread about won't turn a tire on gravel

 

[GMguy84]

On my dad's now brothers Silverado with 4.8 it is a dog with poor fuel mileage. His was a fleet rental when dad bought it. The gearing is terrible. If you take off hard it will spin tires but over 45 mph it revs great only if floor it then runs out gear at 80 mph. It will top out at 100 if you hold it long enough. We got in hilly area in Alabama trying to follow Aunt which she had frt wheel drive Dodge sedan which I was floor most of way and it struggled. Pulled a K Car from Florida to Louisiana fuel mileage was less around 6 mpg at 70.

CR*P ya thats what I found out today. Mine also was a enterprise rental when new. I decoded the VIN and it said "Fleet Sales" and another section Enterprise rental DOH !!!!!!

Meh just a work truck to get around town.

With 100 degree texas heat, A/C full blast at 80 MPH and its topped out. Lost count how many times I have to "Floor it" to the carpet and hit 3K RPM just to pass a car on highway

Mine has the 3:23 rear end non posi. Was getting like 12-15MPG highway with A/C on. I was at 2000 RPM @ 80MPH

Gonna do a trans pan drop Tuesday to see if that changes anything ??? Castrol Transmaxx and new filter/gasket. I did that to my old 02 Suburban and the throttle/pedal response helped greatly !!

Dave

 

[supton]

I could see it needing to downshift for passing. It's a small NA gasser not a turbo-diesel and it's pushing a tall gear in a heavy truck.

2k at 80mph? What size tire do you have? Sounds like 245/70R17. That does calculate out to 2k at 80mph. Poor thing is loafing along at 65! At 80mph 3rd gear would be 2847 locked and maybe 3k unlocked, so I could buy this sort of behavior.

If you drive aggressively and it has to kick down often to 3rd then this mpg might be as good as it gets, once the usual suspects are ruled out (tire inflation, alignment, dragging brakes, plugged cat, etc). I suspect this truck may really need a regear to make it "feel better" which may not impact mpg too badly--it likely won't help but it may not hurt, since the engine may be operating in a better rpm range for you.

 

[OVERKILL]

I could see it needing to downshift for passing.

I would love to have you drive that one my buddy has. "needs to downshift for passing" is the understatement of the century. You need to plan passes and get your foot right in it well before you actually start to overtake, because it is going to take a while. I'm sure there is something wrong with it, as it has this like 500-1000RPM power band at the very top of the rev range just before it shifts, then falls on its face until it struggles to get up there again. I assume the VVT isn't working.

 

[supton]

I would love to have you drive that one my buddy has. "needs to downshift for passing" is the understatement of the century. You need to plan passes and get your foot right in it well before you actually start to overtake, because it is going to take a while. I'm sure there is something wrong with it, as it has this like 500-1000RPM power band at the very top of the rev range just before it shifts, then falls on its face until it struggles to get up there again. I assume the VVT isn't working.

I'll take your word for it. I only drove a 4.8L once (never got to drive a 5.3 or any other truck for the matter), don't recall any issues (3.42's extended cab, but not a quad cab setup) and don't recall it being bad at all. VVT or not, GM usually had a nice flat torque curve on their motors.

You just have to get your buddy to go visit clinebarger or Trav or the like.

 

[OVERKILL]

I'll take your word for it. I only drove a 4.8L once (never got to drive a 5.3 or any other truck for the matter), don't recall any issues (3.42's extended cab, but not a quad cab setup) and don't recall it being bad at all. VVT or not, GM usually had a nice flat torque curve on their motors.

You just have to get your buddy to go visit clinebarger or Trav or the like.

He's actually a mechanic, just hasn't bothered digging into it because the truck is pretty much done as the frame has serious rust and has actually bent a bit so he expects it to be retired here shortly.

 

[BAJA_05]

Buddy of mine has a 2005 2WD 4.8L with 130,xxx miles and his runs like a top. Not like hes trying to smoke the tires or anything but the truck runs GREAT for the age and mileage. I constantly give him compliments on just how it runs and looks -- no rust anywhere neither. He also gets great gas mileage also.

 

[350Rocket]

Buddy of mine has a 2005 2WD 4.8L with 130,xxx miles and his runs like a top. Not like hes trying to smoke the tires or anything but the truck runs GREAT for the age and mileage. I constantly give him compliments on just how it runs and looks -- no rust anywhere neither. He also gets great gas mileage also.

My friend has a rust free 2002 regular cab Short box 2wd with 4.8/3.42 gear. It will spin the tires and has plenty of power. No rust and the interior is like new. About 150k miles. On the highway it got over 22mpg.

 

[01rangerxl]

Yes, the LY2 is definitely not an AFM engine.

Even though you don't have any codes, I wonder if something is up with the drive by wire system, either at the pedal end or throttle body end. It's not uncommon to have to replace either the pedal or throttle body.

Also, GMT900s with the 4.8 are not quick compared to many other trucks with LS engines. The 2012 L20 4.8L equipped truck at work is a dog compared to the older trucks in our fleet and always has been. We have a couple 2004 5.3s with twice as many miles that will blow the doors off the 2012 all day.

 

[OVERKILL]

Buddy of mine has a 2005 2WD 4.8L with 130,xxx miles and his runs like a top. Not like hes trying to smoke the tires or anything but the truck runs GREAT for the age and mileage. I constantly give him compliments on just how it runs and looks -- no rust anywhere neither. He also gets great gas mileage also.

I wouldn't call 130,000 miles high mileage, but it certainly sounds like your friend looks after his vehicles

 

[Trav]

He's actually a mechanic, just hasn't bothered digging into it because the truck is pretty much done as the frame has serious rust and has actually bent a bit so he expects it to be retired here shortly.

No frame no truck. Its a shame they don't do something better with materials for the frame. I saw a 68 C20 the other day in good shape and the frame was good on that old bugger and it sees winters, obviously well taken care of but cripes its over 50 years old.
It makes me wonder if they could do it then whats the story today?

 

[supton]

No frame no truck. Its a shame they don't do something better with materials for the frame. I saw a 68 C20 the other day in good shape and the frame was good on that old bugger and it sees winters, obviously well taken care of but cripes its over 50 years old.
It makes me wonder if they could do it then whats the story today?

Sometimes I wonder if manufacturers don't engage in a game where they might go all out, then slowly cut corners or quality until problems reach a certain point. That way they "know" where the limit (or tipping point) is.

 

[OVERKILL]

He's actually a mechanic, just hasn't bothered digging into it because the truck is pretty much done as the frame has serious rust and has actually bent a bit so he expects it to be retired here shortly.

He sent me some pics of the frame rails last night:

 

[supton]

Bet it rides like a Caddy now, with all that frame flex...

No chance that is a thinner metal to box in the frame? I had an Isuzu that rotted a frame like that--but it actually only looked bad. They welded sheetmetal onto the C, not sure why, but the thin stuff is what gave out. [I had a guy tack in 1/8th plate, stiffened up the works, got a couple more years out of it.]

 

[OVERKILL]

Bet it rides like a Caddy now, with all that frame flex...

No chance that is a thinner metal to box in the frame? I had an Isuzu that rotted a frame like that--but it actually only looked bad. They welded sheetmetal onto the C, not sure why, but the thin stuff is what gave out. [I had a guy tack in 1/8th plate, stiffened up the works, got a couple more years out of it.]

Nope, that's the frame. It's funny, because the body has held up surprisingly well, but the frame is obviously done.

 

[tiger862]

My friend has a rust free 2002 regular cab Short box 2wd with 4.8/3.42 gear. It will spin the tires and has plenty of power. No rust and the interior is like new. About 150k miles. On the highway it got over 22mpg.

My brothers is 3.08 gearing with a tow rating of 6600. Decent highway terrible towing as well as terribly low in carrying cargo. We put 20 boxes of flooring in it and it was squatting badly. Put same flooring only we had all the pads, flooring (pallet) and few other things along with my wife and I. Saturn 4 cyl handled great.

 

[350Rocket]

Nope, that's the frame. It's funny, because the body has held up surprisingly well, but the frame is obviously done.

My 05 needs cab corners and rocker panels, but the frame and floor are mint. The box, doors and one fender are actually mint as well.

It used to get krown rust treatment every second year for about 5 or 6 years until they figured it was end of life. I occasionally had it at my weekend job at Goodyear to get work done and I would spray a whole can of krown on the frame in key areas that are known to rust and that seemed to be enough.

I think they really cheapened up the metals in the gmt900 series.

 

[350Rocket]

My brothers is 3.08 gearing with a tow rating of 6600. Decent highway terrible towing as well as terribly low in carrying cargo. We put 20 boxes of flooring in it and it was squatting badly. Put same flooring only we had all the pads, flooring (pallet) and few other things along with my wife and I. Saturn 4 cyl handled great.

My friends has an extra leaf, so if it will fit in the puny box it probably won't squat much. It rides pretty harsh though between the extra leaf and being a short box.

 

[GMguy84]

Sooooo Anyways lol............ I'm gonna try and trans service pan drop, New fluid,filter and gasket and a MAF cleaning

Think my truck is haunted ?? Tonight on way home from work on highway the gauge cluster starting acting weird, heard a clicking sound ?? radio was shutting off and on and headlights flickering ?? Once I got off highway it all stopped ??

Dave