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Chevy Silverado and GMC Sierra Duramax Fuel Mileage

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Comments

  • kacansas06kacansas06 Member Posts: 33
    A gas engines computer system is even more complex than a diesels due to the emissions control system and the ignition system. Many, Many of the check engine light on situations with a gas engine are due to some component of the emissions system getting old and worn out. A computer code check should tell you what is wrong or at least what system is failing. Most common is EGR valves getting gummed up or Oxygen sensors that are in the exhaust manifold along with an EGT sensor getting literally burned out. Your truck is 7 model years old and was most likely built in late 03 to very early 04 so it most likely has enough miles to make these things a problem. You can replace them yourself if you get the correct diagnosis. Good luck
  • cbears85cbears85 Member Posts: 3
    Thank you very much for your input. Just some added information, my truck is not a diesel and does not have turbo. It has the 6.0L gas engine. Along with the Afe cold air intake, I also had dual Areo turbine mufflers installed. I don't know if that makes a difference or not. I guess I will need to get it on the computer to see what the error code is and then go from there. Also, I will try the mass air flow sensor cleaning and see what that does. Again, thanks for you input and time.
  • hillsdale56hillsdale56 Member Posts: 15
    The guy who wrote post 558 was right on the money. I thought you ran diesel. The reason I said clean the mass air flow sensor is you said you cleaned and I presume reoiled the air filter a few times. The engine will pull oil into air intake, and coat the sensor. You said it went out sometimes. Try it see what happens. If not go get the dtc codes. Hope you find your trouble
  • barrailbarrail Member Posts: 27
    To hillsdale56 , I responded on 1/4/11 but can't find my thread anywhere. So lets try this again. I havea '05 lly with 373's and line in the suburbs of chicago. 500' above sea level. I agree with filling the throte on the fuel tank to check mileage. always buy my fuel at the local Farm Service where the local school busses fill up. Did I understand you correctly to say that you can't run your truck in 6 lockup? Hope this thread gets to you.
  • hillsdale56hillsdale56 Member Posts: 15
    Hey what's up? What you read is true. When diesel domination reprograms the ecm, it brings the max torque to 1900~ 2000 rpm. I have 373 also. My engine runs around. 63 mph. The engine runs stronger in fifth now. The easy tuner has a feature to monitor engine performance. That is sure way to tell. I have to have someone with me to watch the screen and see where the highest turbo boost is. I will post a thread when I do this
  • keygmckeygmc Member Posts: 1
    I Have Solved my mileage problems on my 2008 duramax crew cab 4x4. I was getting 14.7 MPG . I did some research and found that in order for GM to meet the new emission standards they installed a particulate filter in the exhaust. This filter has fuel injected directly into the exhaust for it to work. This results in clean exhaust and poor fuel mileage. Now for the solution. I ordered a tuner the brand is H&S this tuner has a dpf ( Diesel Particulate Filter ) Delete which will allow you to replace the entire exhaust system from the turbo back and not set any codes in the ECM. I installed a new 4" exhaust and cold air intake system ( Banks ) . I could not believe the difference. The H&S system has 4 different power levels I rum on the hot or highest power level for best milage. I am now getting 20.2 MPG around town and 26.1 Mpg Highway.
    I used to have the bully dog tuner on this truck with no milage improvement but good power but with these mods. This truck is pure mean I recomend everyone make these mods. It cost me about $1,200.00 for the tuner and exhaust. Well worth it especialy when I can out run just about any car or truck on the road.
  • hillsdale56hillsdale56 Member Posts: 15
    Glad to read about your good results. Right now I have a half a ton of wood in the back of my ride. With all the snow we are getting here in new york, I'll. Never get stuck. But its killing my city fuel economy. Stay warm
  • fueledupfueledup Member Posts: 64
    I'm real interested in the results you experienced with the H&S tuner. I to have a 2008 2500 duramax that averages around 14 mpg. Which exact set up did you purchase ? Whats involved with the installation? How many miles have you driven with the new tuner? Are you precise with your mileage estimates? What are you getting city and highway? Thanks for your response.
  • kacansas06kacansas06 Member Posts: 33
    With this price just over the horizon again, like back in '08, I know that I can drive my '06 Duramax diesel for much better than the 18 mpg I have been accepting for quite awhile. All I have to do is slow down my acceleration after 30 mph and drive at 55 mph as much as I can. People have short memories but I can say that back in '06 to late '08 drivers of all kinds of vehicles did slow down and did save money. I would expect that driving 15 mph slower will result in a mileage increase of 6 to 7 mpg highway and 5 to 7 mpg city. This is all based on my '06 Duramax results over the last 5 years. I have always tried to drive for better mileage since fuel has rarely been below $3.00/ gallon since I have owned the truck.
  • hillsdale56hillsdale56 Member Posts: 15
    Hi, sorry it has taken me so long to get back to you. We are all feeling the pain at the pump. The mideast is in flames and oil has gone over 100 dollars a barrel. Know the name denise rich ? One of bill clintons inner circle. Her x husband marc rich is the one who put crude oil on the comodities market. The real reason I wanted to answer you is this. Remember my last post I said the wood I was driving around with for almost a month was killing my fuel economy?. Wasn't the wood. It was number 1 diesel. With this winter we have had. They have put a lot of kerosene in the fuel. When it hits 5 bucks a gallon, buy that time we will switch back too 2d . It was 8 degrees in upstate ny, last Sunday morning. What a winter!
  • barrailbarrail Member Posts: 27
    The tip about getting the engine to run at 180 degrees made a little difference in the trucks mileage. If nothing else, the cab warmed up sooner. Bottom line, if you want better mileage, stay off the throttle. I presently have the easy tuner set at 80 e. at the engine responce is very noticible. Fun to drive. Doing more highway driving now, but the mileage still is not 20 mph. stay tuned and thanks for all your input.
  • c_cogginsc_coggins Member Posts: 1
    Interesting reading...

    Our '07 2500 Classic is great but for the mileage... avg. 13 mostly hwy and between 9-11 towing a tiny little 2 horse bumper pull with 2 ponies! Grrr. It's got 55K miles and has been well maintained.

    My old '03 Duramax got 21 hwy 17 city... and towing got around 16 pulling a bigger trailer with bigger horses. I was hoping to get the same or better.

    When I did the research before I bought this truck, all said the mileage was similar to the '03... now I see these threads and wonder what's going on?

    Is anyone out there getting good mileage at all? If so, enlighten us!
  • rgferrirgferri Member Posts: 3
    edited March 2011
    I have a 2006 2500hd crew cab with a 3.73. i was wondering if anyone has some advice for better milage. right now im getting about 11 in the city. was driving a 2004 sierra 2500 and getting 17.5 in city. both truck are bone stock. any pointers?? thanks!!!!
  • kacansas06kacansas06 Member Posts: 33
    first question: is it a diesel??? If not that is about the best you are going to get. Crew cabs weigh a lot more. If it is a diesel then I recommend you decide if you like the acceleration more than mileage. Take it easy on the diesel and you will get better mileage. If that doesn't work then the next easy step is disconnect the batteries, causing a transmission computer reset and then drive it easy. The Allison tranny behind the Duramax is a learning computer for shift points and the more hard acceleration the less up shift and fuel savings. Also the faster you drive the less fuel savings from the engine computer and tranny computer. An '06 diesel is the best one GM has produced lately for mileage.
  • rgferrirgferri Member Posts: 3
    thanks for the advice. Yes it is a diesel. I just purchased it used and the computer said 10mpg and after a few days of driving i brought it up to 11.1 mpg. i have only been driving it for about 3 days now. i am hoping it keeps going up from there. I guess i was expecting mileage like my fathers 2004 duramax. is it taking me longer to raise the mpg because it has been at 10mpg for so long. would re-setting the computer on the instrument panel give me a more accurate reading??? any aftermarket products you guys suggest??? the truck has 104,800 miles on it so i am not worried about the warranty.
  • kacansas06kacansas06 Member Posts: 33
    Oh yeah, reset that stupid display. The DIC that you are getting your MPG stat from arrives at it's calculation from the float position in the tank and the throttle position which means your pedal position as you drive. It is horribly inaccurate and the longer you leave it the farther off it will be. Mine say 14.4 mpg right now because I haven't changed it all winter. Winter is when a diesel gets the worst mileage for a diesel engine is most efficient when the engine is hot. I do not know where you live but here in MN I not only have the "Winter Front" covers on the grill and bumper, I added cardboard from the radiator down in front of the tranny radiator plus I covered the 2 holes left open on the bumper for the tow hooks with cardboard. This winter has been really cold but my drivetrain temps have been good thanks to the block heater and all the covers. No tendency to overheat either even on the few days that have been in the upper 40's or 50. So my calculated mileage at the pump has been 17 to 19 this winter. Close to the lowest I have seen in 50,000+ miles. Spring through fall I get 20 to 22 city(with No load) and when I tow our 16,000 lbs of boat we get 13 to 15. It really matters how you handle the drivetrain. I moderately accelerate to 35 mpg then back off and let it shift to 4th and if needed keep accelerating easy to highway speed. Maximum economical speed is 65 to 67 mph depending on head wind. I can hear the engine start to work harder in 6th with the torque converter locked up somewhere around that speed. It is the complete lack of aerodynamics of the truck which is like shoving a large stack of bricks through the air. But the dash MPG estimate is always off by 3 to 5 mpg or more for me since I have a steep driveway that it has to climb. Also you do not need to idle the truck when you stop to keep it warm for it has a huge amount of fluids that stay warm quite awhile. If you need more advice feel free to let me know if you need my email addy. Oh and if you wish to "chip" your truck get a tuner that connects in the wire connectors under the hood. The ones that plug in inside are DANgerous. For mileage without a load the lower program settings add air to the engine with the higher power setting adding fuel and air. High power settings are for people who need or wish to show off the diesel power but they can easily damage a transmission. The Allison is the "weak" point in the drivetrain but it can handle as much as 15% more power if it is in good condition. To check that have the fluid changed for the external filter has a magnet in it to detect how well it is operating.
  • rgferrirgferri Member Posts: 3
    Thanks a lot. Great help!!! I'm not an aggressive driver by any means, i just want to get better mpg. we never reset my dads in-dash mpg display and for some reason it always ready about 17 city and 21 highway. hopefully like you said with me resetting that mpg feature it will start to show more accurate readings. as for idling the truck, i usually don't let it idle......its garage parked so it doesn't get really cold even though this winter was one of the harsher winters Ive seen. I'm from Michigan by the way....sorry if i didn't give you that bit of info...ha ha so yea we have had a cold one this year as well, maybe not as cold as you guys but close enough.

    Thanks again for all your input and info!!
  • kula_jonkula_jon Member Posts: 1
    Hi, I bought the H&S XRT Pro package with the cold air intake and DPF delete pipe. I just unplugged my EGR and air intake valve connections. I just switched to "hot". I have not seen the gains that you're speaking of, up to this point. I was getting 13.3 and it went to 14.4 but that's all. Am I missing something? I seem to have copied your setup (except I don't have Banks, I have S&B intake).I have a 08 2500 HD with the 6.6 LMM Duramax, extended cab, Allison trans, 4x4 LTZ. I upgraded so I could haul my backhoe. Since it's so dang slow I'm not hauling anything these days.
    I'd appreciate any pointers. Thanks.
  • kacansas06kacansas06 Member Posts: 33
    My quick reply would be that if you didn't replace the computer with one that can work with the stock system you bought the wrong computer. Banks, Edge systems and another all have the purchaser install a "Y" connecter under the hood in the main wiring loop between the stock computer and the engine. They also add an EGT sensor on each manifold. The cold air intake + the bigger intercooler + the bigger exhaust w/o obstructions is how you get to run power levels higher than 2 steps above stock. The upper 3 or 4 power levels are NOT recommended for a stock transmission. Stock Allisons of that year are capable of around 750 ft-lbs without damage. I found all this out for I exceed the GCWR of my truck by about 4,000 lbs when towing our 18,000 lbs of boat & triple axle trailer with us loaded out for a vacation in the bed and cab of our '06 Duramax which still can get 14 to 15 the way I drive it under load with the first 2 power settings. At stock I get 11 to 13. My installer did not disconnect any of the stock systems, just added systems onto the stock which quails more mileage and performance. I did this because I lost so much when 500 ppm fuel became unavailable after '08. My guess is that you have actually hurt your performance and perhaps endangered the engine and transmission. good luck with that.
  • jerryeljerryel Member Posts: 2
    My fuel economy is 14.8 mpg empty according to the truck computer. My 02 Duramax got over 20 mpg empty and around 12 mpg pulling my travel trailer. I only have 1200 miles on the 2011 and baby the engine. I never drive over 65 and most of the time I drive 55 mph. I recently took the truck to the dealer for a diagnostic check and they couldn't find anything wrong? All the reports I have read state that this truck gets from 18 to 22 mpg on the highway empty driving at 65! Is mine just a lemon? or do I need to wait 5000 or 10,000 miles for the fuel economy to improve? My 02 Duramax had a Bully Dog chip set at "towing". It also had the 4" exhaust(no catalytic converter), an Air Raid air cleaner and the Air Raid air intake ring. I love the new 2011 Chevy Silverado but not the fuel economy....Jerry
  • hillsdale56hillsdale56 Member Posts: 15
    Hi, enjoy your new truck. I have an 06, the best year for fuel economy. Your truck will do better as you drive it more. By the time you get to 5000 miles should get better. The dpf kills fuel economy, you will not get the same mileage as with the 02. On my truck, I'm gutting the catalitic converter, and installing a magnaflow muffler. May get like 27 miles to the gallon then. There is no emission test on diesels,, here in ny. Stock pipe is 3.25. I think yours is 7 inches. After you break yours in, contact diesel domination in montana. Check them out on your computer.
  • barrailbarrail Member Posts: 27
    hi hillsdale; when you say your gutting the catalitic converter, are you just replacing it with a test pipe and do you have to reprogram the onboard computer?
  • jerryeljerryel Member Posts: 2
    I owned a 2001 Silverado, 3500 HD dually with the 8.1/Allison. I owned a very large camper at the time(11 1/2 footer that weighed over 5000 lbs). My mileage when I carried the camper was 8 mpg and around 11 empty(at 75 mph){we lived in Nevada at the time}. When I towed and carried the camper my mileage was around 6 mpg(at 60 mph). The truck was very powerful but the fuel consumption was expensive! I have owned a 2002 Duramax and recently bought a 2011 Duramax and find the diesel is well worth the extra dollars for reliability and much better fuel economy.
  • hillsdale56hillsdale56 Member Posts: 15
    What I'm going to do isremove the cat, and run with a test pipe. I'm also removing the stock muffler. Installing a magnaflow. 28 inches long, 3.5 inches in and out. When I get it set up and drive for a while, I will let you know how my milage is. I'm going to bring it back to stock. Tune
  • hillsdale56hillsdale56 Member Posts: 15
    Hello everyone what a storm, upstate ny is a mess. Here are my results. After doing what I said I can get 26 to the gallon with a good grade fuel. I used 3.8 galllons to go 102 miles. City and highway mix use is around 6t00 miles per tank now. Filled to top of neck. Truck does not smoke at idle or while running. I'm happy with it
  • bulldoggit2bulldoggit2 Member Posts: 1
    How do these modifications impact CA emissions tests at registration?
  • barrailbarrail Member Posts: 27
    May I ask, what modifications were made and to what year D-max?
  • hillsdale56hillsdale56 Member Posts: 15
    What I did was remove the cat and stock muffler. Installed magnaflow number 129909. Pipe is stock size. Truck does. Not smoke at idle or when running. Also have a tuner froom diesel domiination. Ruunniing 25 lbs of boost at 1600 rpm. Look into his tuner. Steve shellly s a good guy and kknnows what he's doing. My truck is a 06. 3.73 4wd hd.. now at 420 hp. To answer the post about california, I not familar wth your emission. Testing. Dooo they put a snffer n the tail pipe, use a mirror to look under the truck? Here n new york we don't have that.no. emiissiion testng on diesels
  • chevyhorsegurlchevyhorsegurl Member Posts: 1
    Looking for some advice here folks...
    i drive my truck about an hour each way to work daily, purchased this truck in may of 2011 and was thrilled to see it was getting 18mpg on the drive home! After having the truck a bit i put a soft tonnaue cover on it and immediatly noticed a drop in fuel mileage, to date the truck has been getting around 15.9-16.2 mpg. Wanted to improove mileage so we put cold Air intake system with K&N and did Exhaust with hypertech programmer on stage 2. mileage has not gone up at all since the updates :-(
    Any advice would be much appretiated!!!
  • barrailbarrail Member Posts: 27
    did you rely on the on board DIC to determine your mileage or did you divide gallons put in to miles driven actual.
  • coontie66coontie66 Member Posts: 110
    Back 1.5 years ago the check engine light came on so I took it to the local Chev garage... Five trips later they eventually installed a new turbo in the 06 Diesel Chev. The fuel mileage never returned to its pre FIX of nearly 21 on the road. Now its about 17-18 on the road.

    This week the check engine light came on again so its back to the Chev dealer. This time he says its a glow plug and the EGR/ERG pump and a dirty air filter. The truck went out of warranty in July this year based on years NOT mileage... it now has 45300 on it. During the discussion he told me that the new turbo that they put on about a year ago produces more boost than the factory model AND less fuel mileage. Not happy with that. At first the dealer wanted $1050 to fix my problem but when he was told I would trade it in first he decided to extend my warranty a BIT and cover most of the costs. My NEW cost is about $250. What I didn't tell him is my next attempt to buy a diesel PU would be a Dodge. Sure wish they were quiter.

    I will have to say this 06 Chev is rapidly approaching the top of my list of bad vehicles. So far the Chev Vega of 72 fame and the 80 VW Rabbit are on the top of the list with the 99 Ford diesel in 3rd place. This vehicle is catching up fast and could take 3rd place next year.
  • coontie66coontie66 Member Posts: 110
    About a year ago I had the turbo replaced on my 06 Chev diesel. I thought the fuel mileage had suffered and last week the local dealer told me tha the new turbo produces more boost and the miles is off about 3 mpg. Darn I didn't need more boost just more mileage.

    What to do??? My mileage is about 17---------------grrrrrrrrrrr.

    Mine now has 45K on it.

    Had it in for a gloplug and a ERG pump... warranty ran out in July but they covered both with a 100 buck payment. At first they wanted $1050 until I complained.
  • gmcustsvcgmcustsvc Member Posts: 4,252
    How has it been running, aside from the less efficient fuel economy?

    Best,
    Sarah
    GM Customer Service
  • coontie66coontie66 Member Posts: 110
    I have only really pulled one time with it since the new turbo and that was with my 12500lb camper. It did really fine.. I have not chipped it yet but its loaded with power.
  • cefloydcefloyd Member Posts: 1
    what kind of millage did you get pulling your camper i also have a 12500lb camper and I am looking at a 06 hd3500with a 6.6 or a F 350 super duty with a 6.0 and I know alot of bad stuff said about the 6.0 just checking my options
  • coontie66coontie66 Member Posts: 110
    I was getting 11 mpg pulling my camper before the turbo change... I have not pulled it since the new turbo unfortunately. Both of us have been diagnosed with cancer in the past two years and treated. I think we are fine now just waiting to get time to travel again.. I know that the mileage on the road without the turbo dropped about 2.5 mpg.
  • jimnothappyjimnothappy Member Posts: 1
    I have a vibration in my truck, back to dealer at least 9 times now, no fix, i have 2100 MILES ON IT and i am getting tired of getting the run round . is there a fix
  • gmcustsvcsarahgmcustsvcsarah Member Posts: 1,964
    jimnothappy,

    I'm sorry to read that after making so many different trips in for this to be looked at there has not been a satisfactory resolution for you. If we can follow up with your dealership on this, please send us an email at socialmedia@gm.com with more information (your name/Edmunds username, phone and address, the last 8 of your VIN and current mileage, the name of your dealership, and number of times you've been in for this same concern). My coworker Christina will advise you further.

    Thank you for your patience, and we look forward to hearing from you,
    Sarah
    GM Customer Service
  • kacansas06kacansas06 Member Posts: 33
    You might take it to a place that does over the road (the big semi's) tires and have them check tire balance. I don't think tires are covered under the warranty. Happy hunting.
  • pmeinscherpmeinscher Member Posts: 1
    I have 2007 chevy 4x4 dura max with a milage at about 12 miles per gallon. Was wondering if this unusual or not for that truck I was hoping for much better than that.
  • nater37nater37 Member Posts: 1
    I am very disappointed after owning my dmax for 4 years and only having 22000 miles on it. I get 17.5 mpg empty. I pulled my dads camper to New Mexico this week and pulled it fine, but got 5.6 mpg both ways and it did not matter if I pulled 65 to 75 mph. I thought it was because I pulled it to mountains full of gas and water but empty on the way home and was not any better. The camper only weighs around 7000 lbs. called the dealer and they asked when I had changed fuel and air filters and how much the wind was blowing. The 6.7 Ford is starting to sound nice , although my dads 2012 duramax gets 12 pulling same trailer
  • gmcustsvcsarahgmcustsvcsarah Member Posts: 1,964
    Good afternoon nater37,

    I see you've checked in with your dealership on this; if you want for us to look into this further with you and your dealer's service department please email us the following information at socialmedia@gm.com: your name and Edmunds username, phone and address, the last 8 digits of your VIN and current mileage, and the name of your involved dealership.

    Sarah, GM Customer Service
  • kacansas06kacansas06 Member Posts: 33
    A lot of this kind of fuel mileage problem comes from the driving method. I believe your truck has a tachometer like my 2006. When you accelerate with a big load do not wind the engine to high, say 3000 to 3500, RPM for all it accomplishes is using lots of fuel. When I am towing I rarely let the RPM exceed 2000. When driving without a load I take the RPM at speeds under 35 to 2000 or so and after that take my time and keep the RPM below 1800. Think of it this way, that 6.6 liter engine is more than twice the cubic displacement of a 4 cylinder engine. 4 cylinders go to 3500 to 4000 RPM or more all the time for shifts. So divide that by 2 for the diesel and you get your target RPM ranges. I recently took a fishing trip with 21 ft boat loaded and the truck heavily loaded and made 24 mpg going up north and 22 mpg returning at faster speeds. Oh yes, these truck do not like being pushed to 65 or 75 while towing plus the trailer tires are usually rated for a Max speed of 55 to 65(look at the tire sidewall). I tow our big boat, 17,000 lbs at 13 feet high by 10 feet wide by 45 feet long triple axle, at highway speeds of 55 to 60 cruise and max downhill of 65mph. Doing that I get between 12 to 16 mpg depending on terrain.
  • coontie66coontie66 Member Posts: 110
    I think that there are at least two things I would like to recommend as possible answers to your post.

    The first thing is that your Duramax is not broken in yet and probably won't be for another 30K miles. Patience!

    The second thing is that it seems to me that speed and MPG are inversely related. The faster you go after a certain point the worse the MPG.

    About 6 weeks ago I drove to Winston Salem 150 mile drive and kept the speed on 62 mpg and got 20.2 mpg that was when my 06 Chev just turned 50K. Prior to that time I was getting 17.8 MPG after GM replaced the turbo. The new turbo (probably what you have and much better they told me) actually reduced MPG about 2 and that was back 1.5 years ago. The Chev got in the 20 range when new but not after the new turbo until 6 weeks back.

    Some where you can find the power curve graph for OUR engine. See if you can drive where the power HP and Torque are at its maximum for a certain engine speed measured in revolutions per min. That number will be around 1750 RPM's and will be 60 and 65 miles per hour.

    Keep driving and it will just get better but don't expect it before the engine is broken in.
  • jerrydockjerrydock Member Posts: 29
    Find the sweet spot for your engine. I have a 2005 and 1700RPM is where it likes to be. My wife has a heavy foot and she never gets good mileage from the diesel; so I keep her in the Geo Metro as much as possible.
  • rbboydrbboyd Member Posts: 2
    I bought a 2007 Duramax a month ago and it was getting 15.9 mpg on trip home. I put the chip in it and my fuel dropped to 13.5 mpg. I pulled a small camper trailer approx. 400 miles and got 9.9 mpg. After I quit pulling trtailer just going back and forth to work I am still getting 9.9 mpg. That was with my H&S chip set on "Hot" and not getting into it. I have it turn completly off now to see what happens. I have new fuel filter. Truck has 20" rims & has 6" lift on it. Any suggestions?
  • kacansas06kacansas06 Member Posts: 33
    How many miles and hours on the truck?? How wide is the tread patch on the ground of the tires? When you say "Chip" is it a controller with multiple programs or something that plugs into the data slot inside the cab? The units that plug in in the cab are notorious for causing permanent damage to the engines computers and to the engine components such as fuel injection system defaulting to maximum fuel or burning up the turbo or damaging engine sensors and since the program is no longer stock the trucks computers cannot tell you what went wrong! Last thing is Never, Ever tow with with any computer modification set to HOT since the engine will overheat in many ways that you can no longer know about due to the change in the computers. Good computers that work with the stock computers and do not change the warnings system or the gauge readouts cost quite a bit, on the order of $1500 to $2000, when installed properly. Anything cheaper are the ones that can cause significant damage to the truck. Do Not take it to a dealer, go to another shop that is qualified to work on the Duramax system for diagnosis.
  • rbboydrbboyd Member Posts: 2
    I bought the truck with 84,000 miles on it and it now has 92,000 miles. The hours on engin has been reset. My tire size is 325x12.5x20. I pulled a small camper trailer approx. 400 miles but had my H&S chip set on mild. The H&S chip cost me $1,400 and was installed by a shop in Baton Rouge, LA. that does after market accesseries. It is one you can change on the fly. I am thinking that the shop didn't set the chip correct on fuel. BTW they told me to leave my chip set in the "HOT" setting at all times. The mechanic said I would get mpg because it had the most horse power provided I drived normal & not racing. I have the after market exaust & I put in the K&N air filter. The shop is suggesting the "Cold air Injection" instead. Any suggestions? thanks! I am working a pipeline around San Antonio till after the first of the year. If we rain out I will bring to a shop.
  • rajun55cajunrajun55cajun Member Posts: 2
    I have disagree with the break in part of the comment posted I was told when I purchased a new chevy duramax it would improve as it broke in as to date it has 99186 miles on it and has done nothing but get worse and gm for sure does not have a clue what is going on they will tell you a bunch of bs but no logical answers I started at 21 empty 14 towing a 16000 lb trailer now I am at15.9 to 16.3 at best empty and 10.2 towing my 1500 lb boat one reason I know is the fuel is not worth a crap and gm could give a damn less about so looks like we are on our own
  • kacansas06kacansas06 Member Posts: 33
    I agree with rajun55cajun. Break in of my engine seems to have made little difference in mpg. Tire size made the most difference. I replaced the stock summer tires with a wide all season that had a road contact width of 12" 1/3 greater than the stock after a year. MPG went down by at least 15% to 20%, 4 to 5 mpg. A year and a half later I changed back to a close to stock width of 8.5" and slightly larger diameter and recovered most my mileage loss. Since I have an '06 it is not built for todays 15ppm ultra low sulfur fuel and that has cost me about 2 mpg. So today I can still get into the mid 20's mpg unloaded at less than 60 mph but usually get about 21 to 22. Mixed in city driving is around 18 to 19 mpg. City only with no highway speeds I get 16 mpg. Living in MN I change tires for winter and that takes away another 2 mpg in the city and about 1 mpg highway. I was told by nearly every tuner manufacturer to never run the engine with a much higher than stock program for you may overheat the turbo and other exhaust components such as valves. I was told by many more people that own these to not try to push it to 65 or 75 mph when towing a trailer. My experience with the truck has taught me that 55 to 60 mph towing gets me better mileage and 75 drops it into the 6-8 mpg area which is less than half what the truck can get when towing. I will take 14 mpg towing 17,000 lbs over a little more speed which could ruin parts of the engine and transmission.
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