Didn't think it would happen to me. Used Stanadyne on all tanks so far. Took my truck to dealer to make sure all updates were on my truck, they were. Told them I am only getting 11 mpg. (I know that I have 35's, but come on. My 8.1 would get 9 mpg.) Anyways, they said they would take a look at it and #8 injector was bad. I couldn't tell the injector was bad. It never ran any different since new. Maybe it was bad from the factory. Well, left it there last night and they said it would be done today at noon. Hope this fixes the fuel mileage.

If it's true than it probably won't hurt you mileage. Hope this fixes the problem and all is well after this. Nothing worse than having a brand new truck in the shop. :(

Good luck with your truck later on

mick, let us know if replacing the injector improves your milage.

Well, my injector was replaced and mileage didn't increase. Took a trip last night for five hundred miles with speeds of 70-80 mph. MPG was a little over 12. No improvement in mileage. I hope it gets better with more miles.

Mick

you've got very low miles on it, let it loosen up some. Numerous people here have reported better mileage after the trucks gets some miles on it. I'm talking 10-12k in some cases.

a common thing I am hearing and reading is that the mileage on the first tank is impressive, but it falls after that. In my personal experience with my truck, the milage dropped for 3 tank fulls. Now it is getting better with each tank and climbing each time.

Same here, mileage at the 70-80 mph speeds you mentioned were not good when my truck was new. I noticed improvements somewhere around 10K, and now get 16-19 with 15K, with speed being the determining factor...

thanks for the replies guys. Headin to the mountains snowmobiling this week with the four place enclosed. its a 900 mile trip each way so should help to "loosen" her up a bit.

I hope you get better milage but i wouldnt count on it , 24000km and counting still only getting 12.4mpg on the dic I love this truck But the fuel milage BLOWS compared to my last truck [LB7]

Hey, worse yet. I own an 03 Duramax, I just turned 40,000 on it and it's in the shop right now with a bent push rod and 3 injectors are out if it. In your opinion what do you think caused the bent pushrod??

Well, my injector was replaced and mileage didn't increase. Took a trip last night for five hundred miles with speeds of 70-80 mph. MPG was a little over 12. No improvement in mileage. I hope it gets better with more miles.

Mick
I have around 9,000 miles on my '04 LB7 and it is just now starting to get better mileage. I'm getting 17 city and about 19 highway (70-80 mph). Four months ago, I was only getting 12 mpg city. Many people have said that the Duramax does not need any engine break-in. I have to disagree with them. The change in fuel efficiency that I experienced is due to engine break-in.

you've got very low miles on it, let it loosen up some. Numerous people here have reported better mileage after the trucks gets some miles on it. I'm talking 10-12k in some cases.What changes to allow for the increase?

Is it wear and freedom of movement due to reduced friction, or is the ECM (not sure if that is what a diesel uses) set to only allow so much power during break-in (to increase the overall engine life).

If it were due to mechanical break in, I would assume that the MPG would increase slowly over time, but people seem to be saying that their efficiency changed after X amount of miles.

It would make sense that GM would design the unit to limit HP/TQ until a certain mileage is reached (and/or a certain algorythm had been satisfied) to keep the wear from break-in to a minimum. When the ECM says it is time to up the power, it does so by making the motor more efficient (hence the increase in mileage).

I know several people that have installed aftermarket programmers and have said the power AND MPG have gone up (which leads me to believe that the manufacturer is doing the same thing......maybe even if it's just to keep warranty claims down.......which is NOT a bad thing IMHO). It may even be something only the engineers at GM know (sounds like a conspiracy theory ;) :D )

The other reason I ask this is I heard rumor (take it for what's is worth......probably nothing -:t) that the factory does in fact do this. I have not proven this, so until I do, I'm chalking it up to "Urban Legend".

I know the day I drove my truck home from the dealer I was sick.... It didn't run anywhere near as good as my dad's 02. But now that I have 6,000 miles on it I can tell the power and fuel mileage is really starting to pick up. I'm getting 13 in the city and about 15-16 on the highway...

I have 7500 miles on mine and noticed the mpg starting to go up. There is definitley a break-in time on these engines, mine runs alot better with the current mileage. I drive city and highway, stop & go traffic and I am averaging 17.6-18 mpg per the DIC. 70-75 mph.

I haven't hand calculated yet , but have been reseting the DIC at every fillup.

i only get abou 13MPG on mine.. the most i ever got was 17..

My dad's 02 has 55,000 miles on it.... I have a superchips programmer on it and that is the only thing done to it and the last trip I took it on I was getting 17.8 running 80+ the whole way.

I get 18-19 when not towing. 13 Towing a 12000lb trailer at 75 mph. 23k on the engine. Check your air box for obstructions.

It's strange there is such a difference betweens the MPG people are getting with the LLY. I am very happy with my MPG (-+20) and it has been the same from Day 1 until the reflash. It went up by around 3 MPG.

Now that winter has officially arrived the MPG has gone down and I would expect it too. I tow a trailer that is around 7000 lbs and the mileage is around 13.

Dual rear wheels makes a big difference I believe.... Plus my 05 is a 1 ton crew cab 4x4 dually. Biiiiig weight difference from your 3/4 ton, short bed crew cab....

Also depends on what you have done to it.... I believe any performance mod you make on it, your MPG will increase.

Winter fuel also kills mpg and don't forget about the extra resistance from cold lube.

Aron, u need to add close to 10% on your DIC readings due to tire upgrade so 13.6 or so.

my mileage was great for the first 8,500 empty i was getting 18.5 to 19.8, now for some reason im getting 14-16 at best. the only change ive noticed is if i kick it down i get a puff of black smoke, never got it before.

Almost 12000 miles and normally gets 18 mpg. I was hauling ~6000lb into 25-30 mph winds and got 12.9 mpg. Just changed the fuel filter and the oil to 5w-40 18.2 mpg and climbing. All info is based off of the DIC which is +/- 0.2 mpg.