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2007 and newer Chevrolet Tahoe and GMC Yukon

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  • rockman59rockman59 Posts: 250
    Hello to all, When I purchased my new LT3 '07 Tahoe I was amazed when I raised the hood and noticed that there is not the typical cooling fan and fan shroud.
    ____________________________________________________________
    GM introduced the electric radiator fans in '06 on the Suburbans and I have seen no reports of any overheating problems being mentioned anywhere.
  • jmaynardjmaynard Posts: 37
    Jerry, what you experienced is negative torque. With the engine engaged and running and the coasting going on, there is less pressure as 'some' of the positive torque from the flywheel is redirected back to the engine. Now, that does not mean that the engine can be shut off or fuel is not still being delivered. All that means is that the engine is in a slightly lower idle state with the transmission providing relief. In a previous post I mentioned the injectors misting. This is when this happens. There is just enough fuel going to the cylinders to maintain a burn.

    Now to further prove the point, even though I really don't have to, do this test. While coasting, out of gear, stop the engine by turning the key off. Now, place the gear shift in drive. And continue to coast. Once the vechicle comes to a stop, is the engine running or not. I can answer that question for you, it will not be running.

    Now, to further make the point, while the engine is running and you are in gear coasting, place the truck in neutral and depress the brake until you come to a stop. Is the engne still running? When did it magically turn itself back on? The answer is, it never turned itself off and a 'running' engine requires fuel.

    I think that should be enough for now. If those test don't prove that the engine is still running and using fuel nothing will.
  • chile96chile96 Posts: 330
    Sorry to stray from the topics of cooling fans and V0 vs V4 vs V8 but.....

    Does anyone know how to remove and reinstall the tire pressure sensors on the factory wheels for the '07 model? Or should I just head down to Discount Tire and pay $40 per sensor change :(
  • jmaynardjmaynard Posts: 37
    Why would you pay for any repair to an 07 model. If there is a problem with the sensor it should be covered by warranty (these do not wear and tear). Take it to the dealer and have them replace it for free.
  • chile96chile96 Posts: 330
    I bought a new wheel set.........

    Anyways, after a little research, the tire sensors are connected to the valve stems and the tires need to be dismounted so I went ahead and let Discount do everything. Now I just need to sell the original 17" wheels/tires to make the wife happy and clear out atleast one set of wheels :)
  • chile96chile96 Posts: 330
    Surfed that website and am about to buy the Nav Override Plug-In but had a couple of questions:

    How is it installed and how easy/difficult is it to do?

    Do you like it? Any complaints or praises?

    thanks in advance
  • I just had a problem with my tire pressure sensors as well. I bought my Tahoe with the 20" wheel option. I went to a wheel place that swapped out the same "brushed" look wheels for chromed ones. All of the tire pressure sensors reset except for the left front. The Chevy dealer says it's the wheel guy's fault and I have to pay (or recoup from the wheel guy). The wheel guy says he's done many 07 Tahoes and this has never happened - the sensor is faulty. Whose fault is it? The tire pressure sensor is a nearly $200 part plus installation. I personally feel that it's the wheel guy's fault, but he's not working with me on this. What a pain!!! I just wanted chrome wheels!! It should have been a cut and dried deal - but, of course, there's always a problem. Now I have to take hours to fix something that should have only taken the hour it took to swap the wheels. :cry: Why do we need these sensors anyway, other to cover the automaker's butt if there were to be an accident related to loss of tire pressure?
    The wheels look great, by the way. A definite improvement over the dull finish. So easy, now so difficult... :sick:
  • I'm looking at a new 07' Tahoe. My 5.3L 00' Tahoe hunts for gears a lot in the 60-70 mph rang while pulling a Ranger 620 with 3.73 gears.

    I've heard going to 4.10 gears will have a huge impact on mileage and will run on the highway at higher rpm's. I talked to the people at the dealership about it and they were bascially no help as if they didn't know any more then they could read in a marketing brochure so I have no idea if going to 4.10 gears will reduce the hunting for gears problem.

    Anyone out there with a GM 5.3L with 4.10 gears that can comment? Whatever I get I'm stuck with because it's like $1200 to change out the gears later.
  • I will start by saying that I purchased my 07 LTZ with 373’s and I honestly believe that I made a huge mistake. First from a performance view, the new 5.3, combined with the added weight of the 07 does not have the spirit of my former 03 or 04 Tahoes. Additional from a operating cost perspective, it seams like those who opted for the 410’s are reporting substantially better MPG, see earlier posts. My theory is that with the 410’s the engine needs to produce less energy, therefore the DOD / AFM engages sooner. As for your Ranger, I am currently towing a boat with a combined weight of approximately 4000 lbs, and I travel through the Adirondacks in upstate NY. The 373’s get the job done, however the transmission still hunts, even I the tow mode, and often shifts to second gear, with RPM, s increasing to over 4500. IMHO order the 410’s good luck George
  • muskyhunter -
    I can shine a little bit of light on the issue, as I just made a 800 mile trip pulling a trailer with my '07. My '07 is a 4x4 LT3 with 4.10 gears and Zoomers cat back exhaust. I hauled the trailer empty (approximately 1300#) for the first 400 miles and then loaded with a bobcat for the second 400 miles (approximately 5100-5200#). The trip was from SE Ohio to Mid-Michigan and back. The majority of the trip was fairly flat, with things getting a bit more "rolling" hill type terrain upon getting back into SE Ohio.
    On the drive up, I averaged 16.1 mpg, driving 69mph in Ohio, 74 mph in Michigan, with the "Tow-Haul" button engaged. On the drive up I believe it only came out of OD once and it was on a long grade - but other than that, it stayed in OD. On the drive down, I averaged 13.3mpg running the same respective speeds. Similar to the drive with the empty trailer, the only time it dropped out of overdrive was on long grades but there were probably a dozen grades that were long/steep enough to cause it to down shift, at which point it held 3rd gear until the grade was crested, no hunting back and forth.
    I'm not sure how the wieght/wind resistance of the Ranger 620 compares to my load, but it at least gives you a point of reference.
    Also, just for reference - with the 4.10's you will be running roughly 2150rpm at 70mph verses something 1950rpm with 3.73's at the same speed.
    Hope that helps! :D
    --
    TuscoTodd
  • eliaselias Posts: 1,938
    jmaynard, could you please try to be civil? just because we disagree does not mean we have to be rude to one another.
    perhaps a factor here is transmission type or fuel-injection type.
    my 1989 manual-trans IROC-Z owners manual stated exactly what i am saying - that fuel delivery is *zero* in the situation we are discussing.
    google search a little and you will find folks who have disassembled the GM ECMs, identifying the exact code which does exactly what me and the 89 IROC owners manual said: zero fuel delivery in certain "decel" modes.
    some of the disassemblers even identify some source code literal names which back up my claim. i'm not sure how they came up with literal names via disassembly - maybe someone snuck him a symbol-table from inside GM. or maybe he fabricated his data!
    the VW TDI geeks are also well aware of this "issue" and those who appear to know inordinate details about "how internal combustion engines operate" tend to agree with my assessment. the newbies tend to believe that nonzero fuel is used in the situation we are discussing, since it is counterintuitive.
    also we see a posting here with some empirical evidence with your exact vehicle that tends to support my understanding/claim.
    who knows, maybe GM's technology has "regressed" since 1989,
    or in the throttle-body-injection vehicles since then? (my 89 IROC had tuned-fart-injection (tuned-port-injection)).
  • zepreszepres Posts: 16
    Took my Tahoe LTZ in for what appeared to be an "oil leak" at 2000 miles. Dealer kept it overnight to replace a leaking rack & pinion steering gear (???). Discovered when picking up the truck that the NAV disk was missing. Luckily, the service manager was cooperative and said they would order new one.

    Our first US made car in 25 years. So far so ... bad.
  • jerrywimerjerrywimer Posts: 588
    "While coasting, out of gear, stop the engine by turning the key off. Now, place the gear shift in drive. And continue to coast. Once the vechicle comes to a stop, is the engine running or not. I can answer that question for you, it will not be running."
    Tip- with the key "off", the engine wouldn't start running anyway. I'll give you a point for the fact that even if you simply turn the key back to the "Run" position while continuing to coast the engine won't be running at the end (unless a manual tranny- used this to start one with a dead battery once).

    "..while the engine is running and you are in gear coasting, place the truck in neutral and depress the brake until you come to a stop. Is the engne still running? When did it magically turn itself back on? The answer is, it never turned itself off and a 'running' engine requires fuel."
    First off- the key is still on, the ECM is still receiving power and monitoring the engine "operation" (RPMs, vehicle speed too among other things). So it would be fairly simple to allow the flywheel and transmission to continue to keep the engine crankshaft turning while drifting without actually sending fuel to it (and possibly without firing the spark plugs either)- and simply command normal operation once certain conditions are met (if in cruise, speed dropping below set amount, or if not, rpms go below a given threshold where the engine wouldn't resume running smoothly, etc.).

    So your assumptions are faulty, even if you may be right. Notice I never said that it entirely cut fuel in my prior post, just that it appears to be sending very little if not no fuel in the conditions elias described. It is STILL very possible to command a no-fuel / no-spark state and have the engine still "running". In this case "running" simply means all parts rotating regardless of what is causing that rotation- the starter motor normally does this, and when fuel is sent to the cylinders and spark added, the engine takes over for itself to continue the process. In a drifting vehicle the forward momentum of the vehicle in question can be transferred back through the transmission to act in the same manner as the starter motor, continuing to force the engine parts to rotate normally even without fuel and spark. The ECM simply has to "know" that the engine is "supposed" to be running and monitor conditions to determine the right time to resume fuel and spark to prevent that rotation from stalling. ;)

    That's exactly what the V4 mode does- but only for half the cylinders (and closes the valves as an added measure). This obviously doesn't keep the engine from resuming normal operation with all 8 at any point. And before you say something about the remaining normally operating four cylinders- their primary purpose isn't to "keep the engine running". It's to provide the 'minimum' amount of power needed to propel the vehicle forward in light load conditions. I see no reason GM couldn't combine a zero-fuel programming state (for ALL cylinders) with the V4/V8 operation. Running in negative load situations it would actually be possible to kill fuel entirely allowing the vehicle to drive the engine (as described above). When in light (positive) load situations four of the cylinders would fire with the other four shut down. Then in normal driving all eight would be firing. Not hard to grasp, even with a "basic" understanding of internal combustion engines.
  • Piece of cake to install. There is a video on the website that shows how to do it. look on the left side of the screen for the install button.

    Works like a charm! Love it.
  • tony97gttony97gt Posts: 20
    WHO CARES!!!!!!!! you guys are arguing over nothing. Move on. :sick:
  • fundadfundad Posts: 27
    I have been a mechanical engineer for almost 14 years. There is NO way an engine can run on no fuel. To prove this, use a fuel pressure gauge and test it. There is NO kinetic energy from the moving wheels and transmission that can keep an engine running. There is no mechanical "LOCK" that will turn the crankshaft of the engine to keep it running. Then theres a matter of starting the engine. When coasting, do you here the starter engage? This only works on a MANUAL transmission where the transmission and engine are "locked" together. Also. you can simply watch your tach and turn the key off while coasting down hill in gear. You will see the rpms drop to ZERO. I hate to say it Elias... But you really dont know anything about how a vehicle works.
  • jmaynardjmaynard Posts: 37
    #1705 of 1706 Re: V0, really, i meant it ! [jerrywimer] by tony97gt Aug 24, 2006 (7:05 am)
    Replying to: jerrywimer (Aug 24, 2006 4:14 am)

    WHO CARES!!!!!!!! you guys are arguing over nothing. Move on.

    Tony, I understand your fraustration, but the dialog is important. I am trying to relay a message to all the 07 owners that there appears to be a problem with the fuel usage that GM needs to fix. I am now in contact with GM and have an open case but I have asked others to help me by opening ther own complaints. I am convinced that GM can make our vehicles more effecient. When someone coms out and states that during 'x' operation the vehicle is at optimal effeciency, and I know that this is an incorrect statement, I feel that it undermines the work that I am trying to do. It is important that all the 07 owners band together and fight to et what GM promised us.

    I would love to get this back on topic, but we need for everyone to understand that these vehicles can meet the marketing numbers and GM should help us get there.
  • jay_24jay_24 Posts: 536
    Do you think that GM promised 21 mpg? nope. The government said that. * your mileage may vary.

    For those of you not getting even 18mpg on the highway, what do your Tahoe's have in common?
    3.73 gear?
    17" or 20" wheels?
    4x4?
    using AC?
    tire air pressure?
    What brand of gas?
    does the gas have ethanol?
    Do you brake often when over 40mph?
    average speed?
  • steverstever Viva Las CrucesPosts: 41,314
    While it's easy enough to skip over posts you don't want to read, the zero fuel while coasting issue may be better suited for Auto101: How To and How it Works!. I'd like to hear Shifty's take on engine overrun stuff anyway.

    Here's the link:

    Auto101: How To and How it Works!

    Moderator
    Minivan fan. Feel free to message or email me - stever@edmunds.com.

  • jerrywimerjerrywimer Posts: 588
    Thanks for the link steve. I'll refrain from further discussion of this topic here.
  • steverstever Viva Las CrucesPosts: 41,314
    I suspect there's a bunch of info (and debate) over in the hypermileage threads too in the Hybrid Vehicles board.

    Moderator
    Minivan fan. Feel free to message or email me - stever@edmunds.com.

  • jmaynardjmaynard Posts: 37
    Jay, this is not a case of gettong 18 instead of 21, it is more like a case of getting 13 instead of 21. It is about a feature either working or not working, and GM acknowledging that the feature was tuned to a specific design set which may or may not be what is delivered on consumers vehicles. If GM says that the 5.1 V* with multi-fuel gets 21 on the highway by utilizing V$ mode while driving normal speeds then we should expect to see the v4 mode during normal cruising speeds. If on the other hand it onlly goes into V4 mode when coasting downhill and the milage is not even close to what they advertise, and it appears that dependant on if you select the more expensive gear ration over the stock gear ratio then this is a problem. If you are happy with your vechicle and it is performing to your satisfaction, then good for you. If you check this board and others you will notice that there are a lot that are not happy and feel that GM decieved them. Now, I don't believe that I was decieved, just cheated. I think that my Tahoe, and yours, CAN get close to the advertised numbers, maybe even more. In order for that to happen, GM has to admit that they took short cuts and did not take all the variables of the vehicle into consideration when they developed the program.

    It's your choice, you can sit back and let the rest of us fight for you, or you can get involved. The difference is that if you sit back and nothing happens, you are responsible whereas if you get involved and something gets corrected you get the credit.
  • jmaynardjmaynard Posts: 37
    Sorry for the typos. Small laptop keyboards and large fat fingers don't mix.
  • 73shark73shark Posts: 325
    I called Chevy last nite (800.222.1020) and got a service request no. assigned. Spent about 20 min describing how the brochure and Chevy website both state that on level roads at cruising speed, it will go into V4 mode. I explained that mine does seem to do that in the tow/haul mode some times but not in normal mode. Also mentioned that a lot of people with the 4.10 ratio are getting better mpg and staying in V4 mode. I'm with you on your theory that if enough people complain, Chevy might fix. If they don't, maybe the tuner people could do it. There is no reason that 160 hp can't move the beast at 60 mph on level hiway w/ no head wind.
  • jerrywimerjerrywimer Posts: 588
    It's not 160hp except in V4 mode at 5200 rpm (hp peak). I doubt ANYONE will ever see it putting out 160hp in V4 mode because of this (short of catastrophic failure of the lifters or something, preventing the engine from going back into V8 mode while the engine is wound way up). I'd love to see the hp and torque curve chart for these 5.3l AFM V8s, so we could say exactly what the hp is at normal cruising speed and RPMs with each gear ratio.

    That might shed some light on things, because for one thing, I'm beginning to suspect the reason us 4.10 owners seem to be seeing better results is that the engine is running at over 2100 RPMs at 65 mph, vs. the just under 2000 that 3.73 rear end vehicles are doing. Perhaps the actual V4 hp produced is just enough for the 4.10 gears to pull our weight in level or slightly uphill inclines /very light throttle acceleration while the 3.73s are just too tall for the slightly lower hp produced at under 2000 RPMs in V4 mode. I recently found that my AV will actually allow me to accelerate very slowly on level ground at around 60 to 65mph without going back into V8 mode and that it will also stay in V4 mode on extremely light grades with no headwind at similar speeds.
  • nosbor77nosbor77 Posts: 40
    I haven't noticed V4 lightly accelerating around 60 to 65 mph. But I have the 3.42 gear ratio. I did play around with the to mode on. I noticed if I have cruis control set at 48-49mph with tow mode on, it almost always stays in v4 mode on unless on an incline. Kinda cool.. but yes, they fooled us. I will try to call too..
  • jmaynardjmaynard Posts: 37
    I would be interested in where the HP number of 160 was derived in V4 mode. I have not ready any statistics but would be very interested in what the actual HP is in V4 mode.

    Thanks everyone who is calling and opening a case. The more they hear about it, the more inclined they are to look into it.

    Jerry may be onto something with the HP being a factor in the mode switch. All GM technicians say is that there are a number of factors that determine when the engine switches. I know that it can only run in V4 mode for 10 minutes at a time before it has to switch back (computer setting). I assume this is to insure that the idle cylinders are gerring appropriate lubrications. I also suspect that there is still a vaccume sensor somewhere which makes contact as soon as a load more than [X] is placed on the engine. This would on place to look for a problem. I would appreciate it if GM would release how the entire systems works and exactally what can or will not allow the switch to take place.

    Again, thanks to everyone who is moving forward with this. I believe that we can make a difference and institute change.
  • 73shark73shark Posts: 325
    That was just a quick number (half of the rated 320 hp). I realize it would be somewhat less due to the frictional losses of the unused, rotating four cylinders.

    My guess is that it senses when the cruise control can't maintain speed, it kicks into V8 mode. But it's probably more sophisticated than that. I agree that it would be nice to be able to make it a little more agressive to go/stay in V4 mode.
  • kssoonerkssooner Posts: 10
    I called Chevy last night at 800-222-1020 and received a service request number assignment. I complained about the V8/V4 mode of operations or better the non-V4 mode. I have the 3.73 gears and mine is never in V4 unless going downhill or coasting. I have seen it in V4 if and only the tranny is tow-haul mode and under 60 mile an hour, but the calculated mpg in V4 mode is around 18-20 with the tranny NOT in tow-haul but motor in V8 mode the mileage is basically the same 18-20 a wash there. I live is north central Ks and some of the roads are very flat and straight, but still V4 is almost non-existent. The Chevy hot line to me was of no help at all. I ask if many calls about this so-called new idea for better mileage been received and the answer was NO not many, so I guess that's why there are some many new Tahoes still sitting on the lots in this area of the country.
  • stakeoutstakeout Posts: 173
    guess GM/Chevy/GMC are scrambling these days.. so they came out with this... which they should have included in their early release '07 models.. pressure was on them and they couldn't deliver.. why.. because they didn't care all those years of dragging their butts along with Ford and Chrysler with mileage #'s on their trucks.... now they're hurting...losing all that bizness to foreign mfgr's
    http://www.usatoday.com/money/autos/2006-08-25-gm-engine_x.htm

    they had no bizness coming out with newer SUV/truck styling early.. their marketing gurus blew it big time.. they panicked because of the gas $$$$...and patched a fix with the on demand V8/4 thingy

    I've got until early March to choose what I'll be getting to replace my '04 'burban 4x4 lease... the way it's going.. bye-bye Chevy after we've had four 4x4 'burbans since '99...unless they sweeten the pot a whole lot... so far with that new styling.. arggggghhhhh... :mad:
This discussion has been closed.