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Old 12-08-2003, 11:55 AM
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Quote:
Originally posted by Dave1972
Cold start knock--
I have a 2001 1500HD 6.0 with the 373 gear. I put 265s on it when I bought it and the gas milage sucks. It gets around 11 to 12 in town and not much better on the road maybe 13 to 14. I tow a 280 Velocity and get less than 10 at 80+ mph. But the truck tows the boat great.
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Old 12-08-2003, 11:56 AM
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OK, just found the info I was looking for,

Check this out Tim,

Engine Knock on Cold Start

1999-2002 Chevrolet and GMC C/K Pickup and Utility Models

2002 Cadillac Escalade (2WD)

with 4.8L, 5.3L or 6.0L Engine (VINs V,T,U - RPOs LR4, LM7, LQ4)

Some of the above vehicles may exhibit an engine knock noise that begins in the first 19,000-24,000 km (12,000-15,000 mi) of use The knock noise is most often noticed during initial start-up and typically disappears within the first 5-30 seconds (may last longer in extreme cold temperatures). The noise is usually more noticeable on the initial start-up when the temperature is below 10 degrees C (50 degrees F) and may be more pronounced on the first cold start following a long trip.

This noise may be caused by an interaction between carbon that has formed on the piston, the piston motion and the cylinder wall. GM Powertrain Engineering, and an analysis of engines with this condition, has confirmed that the noise is not detrimental to the performance, reliability or durability of the engine. THIS NOISE DOES NOT HAVE ANY EFFECT ON THE LONGEVITY OF ANY OF THE ENGINE COMPONENTS.
Important
At this time, attempts to repair this condition by replacing the engine assembly or pistons is not recommended.
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Old 12-08-2003, 12:01 PM
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rchevelle,

Good post about the knock but the source is GM. Of course they wouldn't say anything bad about their engine! A knock in any engine is not "normal" nor can every one be diagnosed as a "carbon buildup". I have never had a single problem with the engine in any of my trucks and I've had 3 new trucks in the past 5 years. Just pointing out that GM won't admit they have a problem. My truck had the knock from zero mileage!
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Old 12-08-2003, 12:09 PM
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According to this article, they have fixed the problem, Why would they fix something, if nothing were wrong???

http://www.freep.com/money/autonews/...4_20031114.htm

I agree, the carbon will not destroy the cylinder wall, but it IS annoying, I dont mind so much now that I know they all have it, I was embarrassed to ask anyone about it, I thought I bought a lemon!!!!!!
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Old 12-08-2003, 12:16 PM
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rchevelle,

Nice post and good info. Depends on how much you want to fight the problem I guess. I'm planning on keeping my truck for a while so perhaps I should start talking to someone about it! I've got 25K miles on my 2002 so I should report it a few times just to cover my a$$ I suppose. A new engine would be nice but doubt that would happen.

I know what you mean though as it is kind of embarassing with a new or like-new truck that knocks like it's going to fall apart!
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Old 12-08-2003, 03:44 PM
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Ok, after reading all of your posts, it seems like the 6.0 and the 8.1 get close to the same fuel economy. I have heard of rare occasions where the 8.1 gets 9-10mpg tops with a 4.10 gear. Griff quoted economy numbers of 11-12 in town and as high as 14.2 hi way. It seems like 12-13 mpg hiway is about the norm with 8.1 w/ 3.73 gear.
On the other hand, it seems that the 6.0 w/3.73 gear isn't much better. Chad was getting 11-13 with a 4.10. Formula1 got 13 with a 3.73. Dave1972 was getting 15-16 with 3.73, but was that before mods or after?
I'm trying to get all the numbers in a column, but I don't seem to be doing a very good job here. Maybe I should find some way of doing a spread sheet, or just start a new thread asking for fuel economy numbers of 2500's and ask to list engine choice and gear ratio...
I guess the reason I've been so torn on this is that, I would love to buy a new truck. BUT, I currently own a 1996 GMC K1500 ext cab 350. It pulls 26' to 28' singles with no problem, and has pulled 8000# plus 31' twins on many occasions either to Perry or the Ozarks. Granted, those bigger boats set it down a bit in the rear and you certainly plan your stops in advance.
Coming back from the Milwaukee race I got 19.4 mpg running about 75mph. Coming back from the Orange Beach race I got 19.6mpg at around 70mph. Both times we were heavily loaded with tools and parts but not towing.
Did I mention she turned over 248,000 miles on the way home from OB?
Someday I'm going to unload all my stuff and take a trip running a constant 60mph just to see her get over 20mpg.
My point is, I should have run the wheels off this truck by now, but it runs better than ever, and shows no signs of giving anything up. So, hopefully you can see my problem. As many miles as I put on a vehicle, fuel economy is important to me. However, I am not into diesels, period! So, is it possible to get an 8.1 with a 3.42 gear? For that matter, I'd take a 6.0 with a 3.42 gear if they made it. I don't need to set any acceleration records off the line, and I don't care if my mileage drops when towing.
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Old 12-08-2003, 03:59 PM
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Gordo-
I wouldn't try for any 3.42 gear... It'll cause the engine to lug too much. Trans heat will increase as a result.

I had a '94 with a 454 and 3.73s. Then I put 285/75-16s on it... then the overall garing was too tall. Fuel milage increased a bit when I put on the big doughnuts...
Towing took that truck from good to poor in my opinion. The temp would rise when towing in OD, and it wouldn't stau in OD, even though the engine had plenty of torque... I had to run 75-80 to keep the thing in OD...
I'll never make that mistake again.
Keep at least the 3.73s.
250,000 miles... I'd keep what you have for now. The truck is probably worth more to you than to anyone else. Nobody will want to give you anything for it.

I'm leaning toward the 6.0 with 4.10s and locker. I'll free up the exhaust, K&N, and get the power programmer.
FYI, the K&N alone will help your milage. But don't get stupid an cut holes in your airbox. Hot air doesn't build HPs...
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Old 12-08-2003, 04:01 PM
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My 2500 AV with the 8.1L and a 4spd Auto, NOT the Allison, 4.10 gears; gets 9-10 daily, and less than 7 towing 7K lbs.

I have added wider/bigger tires, true dual exhaust, K&N FIPK. I use to get about 11 mpg daily before I did the mods and started sticking my foot in the injectors so much.

Last edited by Sydwayz; 12-08-2003 at 04:24 PM.
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Old 12-08-2003, 04:19 PM
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griff- are you sure you calculated your averages correctly??? those seem high compared to several of my friends avg's with 8.1L/allison combo. given the manner in which i drive, i would probably get 8-9mpg with the 8.1L.

chad
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Old 12-08-2003, 04:27 PM
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Good comment Tim G! Holes in the airbox will only get you more hot air. The UPD intake is the way to go in my opinion...it looks great, in theory it functions great, and uses a K&N with the stock airbox. UPD Website

Gordo,

I didn't have my truck long enough without mods to calculate MPG. My 15 mpg hwy is with mods currently including programming for 93 octane with the hypertech programmer. For your fact-gathering I thought I would mention, my truck is an 02 GMC 4X4 crew cab with stock tires (will get just a little taller when they wear out). I'm not sure of the gearing in the rearend but I'm confident that it's a 3.73.
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