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03 Duramax performance question

Old 02-26-2020, 06:22 PM
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Default 03 Duramax performance question

Hey guys, I have an 03 2500 DMax that is still stock. I keep seeing things about all of the tuning and programmers and stuff on them and really don't know crap about it. Not really looking for a super truck, but was wondering if it would be possible to get better economy out of the old truck when towing. Right now I am towing a Carolina Skiff 23 Ultra Elite, and when I get the boat back there on the highway I am only getting about 13 mpg, and getting around 17 not towing. I keep seeing things about guys getting in th e20's after they do some tuning or work to their trucks and was wondering if anybody had any experience with this and if that kind of performance was possible on older trucks.
Old 02-26-2020, 07:07 PM
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Something must not be right. I have 03 Dmax and my combined is 19-20 mpg, 23-24 on highway if I'm not driving like an asshole. I towed a 14k boat around and would get 12. This is with Edge/Attitude but only on level 1 (40hp). Its an improvement over stock, but only a few mpge. Remember the more weight you are pulling the less add HP you should run because you increase your EGTs.
Old 02-27-2020, 07:50 AM
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how fast are you running when towing and getting 13mpg? in an 03 with a 5 speed, anything above 65 mph and the rpms really start climbing which means burning more fuel!

to answer your question, yes a simple tune can gain around 3mpg. not all tunes are created equal either!
Old 02-27-2020, 07:56 AM
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Are you towing in tow mode? I get 15-16 towing my contender, 20 plus not towing on interstate. 02 Dmax economy tune, turbo back exhaust and boost valve
Old 02-27-2020, 10:50 AM
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Those first gen Duramax were not as efficient as later ones. His mpg is not that bad....

How many miles? Original injectors? How are your balance rates? Has someone inspected the turbo or done work on it?

You have to be careful with those early Allisons, to much hp and you burn it up.

Old 02-27-2020, 02:05 PM
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OK, to answer what I can, when I am towing I don't really pay attention to the speed on the highway as much as the rpm's. Try to keep them under 2000k which I think puts me right around 64 or 65. My boat is not heavy, 23' Carolina Skiff ultra elite. I do not tow in tow mode. Truck has 135k miles on it and still on original injectors. Not blowing enough exhaust to be concerned about injectors according to my mechanic, who is a Duramax fanatic and has 2 himself and keeps trying to get me to sell him mine. I am not sure what a balance rate is Avalon, so can't help there. Let me clarify first post, 17 is my overall MPG. I do not drive the truck enough to know what the highway miles would be without the boat. I use the truck to run errands locally and then to tow the boat. Not at all a daily driver. LOL< maybe all the fuel is evaporating.
Old 02-27-2020, 05:34 PM
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Originally Posted by avalonandl View Post
Those first gen Duramax were not as efficient as later ones. His mpg is not that bad....

How many miles? Original injectors? How are your balance rates? Has someone inspected the turbo or done work on it?

You have to be careful with those early Allisons, to much hp and you burn it up.

Mileage from my 2002 - same LB7 motor as OP's 2003 (since new and hand calculated)

Cruise set to 75 on the highway - no load = 19.666666666666666666 mpg
City unloaded - average is probably around 16.5-17 but if I drive like a paw paw, I've seen 18.6 MANY times. If I drive like an ass, around 15 mpg.
Towing 10k lbs boat on highway with cruise on 72 = 10 mpg
Towing ~4,000 lb tandem boat highway 70-80 = ~13 mpg
Towing a 7x16x7 enclosed trailer highway = ~13 mpg
Towed a loaded down 8 x 24 x 9 enclosed race trailer 300 miles in January with cruise set to 65. Guessing trailer and load was close to 9,000 lbs? - Load was ~6,500 lbs. Averaged just under 13 mpg.
Best I EVER got - back roads trip - no interstate taking it pretty easy. Top speed of 70 and lots of small towns with 25-45 mph speed limits, stop signs and stop lights. Got 23 mpg.
Old 02-27-2020, 06:05 PM
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Originally Posted by Back-in-Black View Post
Mileage from my 2002 - same LB7 motor as OP's 2003 (since new and hand calculated)

Cruise set to 75 on the highway - no load = 19.666666666666666666 mpg
City unloaded - average is probably around 16.5-17 but if I drive like a paw paw, I've seen 18.6 MANY times. If I drive like an ass, around 15 mpg.
Towing 10k lbs boat on highway with cruise on 72 = 10 mpg
Towing ~4,000 lb tandem boat highway 70-80 = ~13 mpg
Towing a 7x16x7 enclosed trailer highway = ~13 mpg
Towed a loaded down 8 x 24 x 9 enclosed race trailer 300 miles in January with cruise set to 65. Guessing trailer and load was close to 9,000 lbs? - Load was ~6,500 lbs. Averaged just under 13 mpg.
Best I EVER got - back roads trip - no interstate taking it pretty easy. Top speed of 70 and lots of small towns with 25-45 mph speed limits, stop signs and stop lights. Got 23 mpg.

Based on your numbers it sounds like I am right in line with what you have. Does yours have any type of tuner or anything like that.
Thanks
Old 02-28-2020, 12:36 AM
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Originally Posted by dpcarson View Post
Based on your numbers it sounds like I am right in line with what you have. Does yours have any type of tuner or anything like that.
Thanks

No tuner. bone stock and 410,000 miles.
Old 02-28-2020, 03:55 AM
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Originally Posted by Back-in-Black View Post
No tuner. bone stock and 410,000 miles.
Hope mine will last that long too. My mechanic has one customer that owns a minnow farm and has a 2001 Duramax with over 600k on it. He said he has to change the injectors about every 175k miles. Have you had to change injectors any on yours?
Old 02-28-2020, 04:21 AM
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Originally Posted by dpcarson View Post
Hope mine will last that long too. My mechanic has one customer that owns a minnow farm and has a 2001 Duramax with over 600k on it. He said he has to change the injectors about every 175k miles. Have you had to change injectors any on yours?
I just did mine. Truck has around 240ish miles, not sure if theyve been done before. Bought Bosch Remans from Lincoln diesel specialties. If you plan on keeping the truck forever SAC00s would be the way to go.
Old 02-28-2020, 06:21 AM
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Originally Posted by dpcarson View Post
Hope mine will last that long too. My mechanic has one customer that owns a minnow farm and has a 2001 Duramax with over 600k on it. He said he has to change the injectors about every 175k miles. Have you had to change injectors any on yours?

Yes - mine go out every ~80k miles give or take a couple of thousand. It's been the one major disappointment with the truck. It's not terrible but it still sucks. I had 2 set replaced under factory warranty and did 3 sets myself. As Matt said above, the SAC00 style injectors are now available for these trucks. That is THE way to go if you ever have to replace yours. SAC is the injector nozzle design that they went to after they discovered the problem with the LB7 VOC style nozzle design. It's what's in all the Duramax trucks from 2004.5 thru 2017. In '17 they ditched Bosch and went to a Denso injection system and they may still use the SAC type nozzle design, I just don't know. Anyway, it is possible that a SET of SAC type injectors will last the life of your truck. It's a totally different nozzle that is not susceptible to the type wear that the VCO nozzles are.

There is a guy over on the duramax forum that has ~1.3 million miles on his 2002 at last report - maybe 3 months ago. His new goal is 1.5 million.

Your truck will probably outlast you if you maintain it. Other than injectors and a leaking oil cooler gasket, I have had ZERO problems with my motor or my Alison. The oil cooler gasket cost about $60 to fix. Plenty of repairs / replacement of worn out U-joints, bearings, and suspension / steering parts but no drive train problems other than stated.
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Old 02-28-2020, 07:49 AM
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Originally Posted by dpcarson View Post
Hope mine will last that long too. My mechanic has one customer that owns a minnow farm and has a 2001 Duramax with over 600k on it. He said he has to change the injectors about every 175k miles. Have you had to change injectors any on yours?
B-N-B is going to be your go to guy with this make of duramax! he knows it inside and out! he has done all the research and numbers for them!

also one hell of a stand up guy! sent me some helpful info when we were building shops at the same time!
Old 02-28-2020, 11:16 AM
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I would say the engine is running within standard parameters given the age.

Balance rate is to make sure the injectors are all within a given flow rate. If one is way high it will mess up you mpg but won't really notice it while driving.
Old 02-28-2020, 11:48 AM
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Yeah, here's the way I understand the balance rate thing. The ECM monitors individual cylinders ( I guess for power or something 'cause nothing else would work for what they are doing) and if something is "out of balance" then the ECM will adjust fuel rates for the individual cylinders to balance it out. So, for example, if your #1 injector was dribbling fuel into the cylinder (what happens when the injectors go out - the nozzles will no longer seal and they dribble fuel) then the ECM may increase or decrease the amount of fuel being delivered to the cylinder opposite to #1 in the firing order to compensate. Let's just say that's #2 cylinder. So if that's happening, you would probably see a high number in the balance rates for cylinder #2. The problem is actually with #1 but that's not what shows up in the balance rates - it's the compensation that shows up... The ECM doesn't know that #1 is leaking, it just knows it has to add more fuel to #2 to balance it back out. You will get a "balance number" for each cylinder when you connect to the system. The closer to 0 that all 8 numbers are, the better the system is doing - less compensation by the ECM. Numbers will show up for each cylinder as + or -, adding fuel or decreasing fuel to each cylinder. I think that I've read that pretty much anything under +/- 5 is ok but when you get 1 or more cylinders that are causing the ECM to exceed + or - 5, you have a problem. With LB7s, this usually means that the needle / seat of an injector has eroded with wear and is no longer sealing and fuel is dribbling out even when the injector is "closed".

For about $5 you can put the Torque Pro app on your smart phone. Then you will need a bluetooth OBDII adapter to plug into the port under your truck's dash ($15-$50 at Amazon, Walmart, etc depending on connection speed you choose etc). With those 2 things, you can use your smart phone to check your injector balance rates, check fault codes, clear codes and some other stuff. I did this some years back and it was probably one of the best ~50 bucks I ever spent.

Last edited by Back-in-Black; 02-28-2020 at 11:53 AM.
Old 02-29-2020, 05:06 AM
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Originally Posted by Back-in-Black View Post
Yeah, here's the way I understand the balance rate thing. The ECM monitors individual cylinders ( I guess for power or something 'cause nothing else would work for what they are doing) and if something is "out of balance" then the ECM will adjust fuel rates for the individual cylinders to balance it out. So, for example, if your #1 injector was dribbling fuel into the cylinder (what happens when the injectors go out - the nozzles will no longer seal and they dribble fuel) then the ECM may increase or decrease the amount of fuel being delivered to the cylinder opposite to #1 in the firing order to compensate. Let's just say that's #2 cylinder. So if that's happening, you would probably see a high number in the balance rates for cylinder #2. The problem is actually with #1 but that's not what shows up in the balance rates - it's the compensation that shows up... The ECM doesn't know that #1 is leaking, it just knows it has to add more fuel to #2 to balance it back out. You will get a "balance number" for each cylinder when you connect to the system. The closer to 0 that all 8 numbers are, the better the system is doing - less compensation by the ECM. Numbers will show up for each cylinder as + or -, adding fuel or decreasing fuel to each cylinder. I think that I've read that pretty much anything under +/- 5 is ok but when you get 1 or more cylinders that are causing the ECM to exceed + or - 5, you have a problem. With LB7s, this usually means that the needle / seat of an injector has eroded with wear and is no longer sealing and fuel is dribbling out even when the injector is "closed".

For about $5 you can put the Torque Pro app on your smart phone. Then you will need a bluetooth OBDII adapter to plug into the port under your truck's dash ($15-$50 at Amazon, Walmart, etc depending on connection speed you choose etc). With those 2 things, you can use your smart phone to check your injector balance rates, check fault codes, clear codes and some other stuff. I did this some years back and it was probably one of the best ~50 bucks I ever spent.
Which bluetooth OBDII adapter do you use to be able to read balance rates?
Old 02-29-2020, 10:07 AM
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Any of them should do it but I bought one that had a faster data rate - which I'm sure the VERY limited control system on my first gen duramax doesn't need.

Anyway, I bought the OBD Link LX. Just looked it up on Amazon - it's $49.95 which is right about what I remember paying for it 4-5? years ago. There are cheaper ones that will work probably just as well and there is at least one that cost more than twice as much.

I've used mine, along with Torque Pro on several of the family cars and it's worked on all of them. Mainly when a check engine light comes on I'll use it to get the code(s) and then look them up on the internet. So far, it's worked on the wife's Mecedes diesel, son's Mercedes gas, wife's old car which was a 2011 Camaro and DIL's Dodge. It's worked on all f those plus my truck although in 18 years I've only had 1 code on the truck and that was a glow plug relay that fixed itself before the parts I ordered arrived. I mainly use it on the truck for balance rates. The first gen duramax systems don't seem to have very robust control systems. A lot of the sensors listed are just not there on that old thing.

Torque Pro is also great for clearing codes.
Old 02-29-2020, 10:40 AM
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From my understanding, the LB7 is the best on economy out of all the Duramax's...

Empty highway, I average 23-24mpg in my LBZ, towing my 22ft CC flats boat about 17mpg.

Mine is tuned Kory Willis PPEI 100hp, 4" turbo back straight pipe, EGR delete, CAI...

If you do decide to tune, be careful with how much power you put in it and how hard you run it... Those 5 speed Allison's don't like much more power over stock, and if you run it hard all day everyday you will limp it and start slipping. Instead of tuning I would do other things to help economy like a straight pipe and cold air intake (your truck doesn't have an EGR unless it's a California truck.)

Just be careful with what tune you throw in it..
Old 02-29-2020, 10:57 AM
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LB7 in stock form is not the most efficient engine, certainly not as efficent as the LBZ or even my LML. I would get 20+ on the highway with my 2015 Crewcab not towing.
Old 02-29-2020, 11:08 AM
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The LB7 actually might be the most "efficient" as it has a higher compression ratio than later models. The 5 speed vs. 6 speed Allison may be the real difference maker there. They dropped the compression ratio on later models half a point as a noise reduction step. In comparison with late model diesels, my LB7 is LOUD. But yes, I see lots of guys with later models getting 20 mpg or maybe a little better at highway speeds. I have never busted 20 mpg on the interstate - I almost always set my cruise for 75-77 mph on the interstate and if I'm going slower than that, it's because traffic really sucks or I'm towing. In either of those cases, I'll get worse than 19.66 mpg.

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