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2007 and newer Chevrolet Tahoe and GMC Yukon

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Comments

  • jmaynardjmaynard Member Posts: 37
    Elias, I really don't want to insult you, but engines do not run without fuel. The 2007 Tahoe has an electric fuel pupm which is constantly feeding fuel to down the line to the injector system. During throttle operations, a valve is opened to allow 'MORE' fuel to flow to the injectors. Durig idle, or coasting, a steady mist of fuel is injected into the cylinders in order to keep the engine running. Without fuel, the engine will stop. This is a physical law and there is no way around it. Something MUST provide energy to make the crankshaft turn.
  • fundadfundad Member Posts: 27
    it would be counterproductive and wasteful for the ECM to pump any fuel during foot-off-gas/deceleration, as long as RPM is ~1000 or more

    What makes you think you can run an engine at 1000 rpm with out using gas??? If it didnt use fuel when coasting, the engine would simply shut off and you would no longer have power brakes or power steering. If you believe that there is no fuel being used during coasting... I have a 80 mpg carb to sell you for your new tahoo. lol
  • 73shark73shark Member Posts: 325
    If the fuel is shutoff when coasting, then why does the engine keep running when trans is put in neutral? :confuse:
  • 73shark73shark Member Posts: 325
    If that's so, then there are a lot of recent reports and studies that are wrong. Don't forget that the main reason Brazil can make it work is that they start with sugar. ;)
  • catahoecatahoe Member Posts: 15
    There are alot of bias and incorrect reports about E85 and any alternative fuels. Just look how many years now that oil has blocked any alternatives.
  • fundadfundad Member Posts: 27
    Another problem with ethanol is that it takes more energy to produce than you get when you use it.

    Not true!!! A by product of making ethanol is corn oil. Corn oil can be used to make biodiesel. If Ethanol uses ALMOST the same amount of energy to produce than what it can give, corn oil is ALMOST free then. I live in Minnesota and it has become VERY profitable to make ethanol now. Infact, there are 2 plants here that will be built that will produce more than 500 million gallons of ethanol each per year
  • 73shark73shark Member Posts: 325
    Here's a couple of articles that shed some lite on the rush to ethanol:

    http://healthandenergy.com/ethanol.htm

    http://money.cnn.com/magazines/fortune/fortune_archive/2006/08/21/8383659/index.- - htm

    I agree that you have to be skeptical about these reports that support or not the use of ethanol. As an example, the same "scientists" that are now warning us about global warming were telling us in the 70s about the coming ice age and we would run out of oil in 20 years.
  • mobile1mobile1 Member Posts: 4
    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. This is the first design I have seen with an engine of this size without a constant cooling source to keep air moving through the radiator.I know Honda and majority of foreign cars use electronic fans but they are smaller engines and typically transverse mounted. I am concerned about in the event of a 2hr traffic standstill pulling the boat and the outside temp is pegging 100 will the electronic fans do a better job.Certainly a belt driven mechanical fan robs h.p.but they wont fail unless the belt breaks. I think we will need to keep and eye on these two electronic fans and make sure they dont freeze up. What are your thoughts. Oh yea, by the way are you guys buying your oil filters from the dealer? That's the only place I have yet to find them. AC PF48
  • steverstever Guest Posts: 52,454
    Live green, go yellow, enjoy the subsidies. :shades:

    More in this collection of discussions: Ethanol - E85 FlexFuel
  • 73shark73shark Member Posts: 325
    I've had starters, alternators, and batteries fail. Have yet to have an electric fan fail. Always a first time tho. Haven't checked it out yet but I suspect that one fan comes on when needed and if it can't provide enough cooling, the other kicks in. Also one probably comes on whenever the A/C is on. Just a guess but based on previous GM cars I've owned.
  • sastokersastoker Member Posts: 11
    I installed a Gibson exhaust system (cat back) (P/N 615562) for my 07 Yukon on Friday 8/18. It is awesome. The sound is great and it doesn't sound nasty when you mash the pedal. The system fit perfectly and was a quick install. The hardest part was using a hacksaw to cut the OEM pipe out. I don't have a sawsall.
  • sastokersastoker Member Posts: 11
    My Yukon (5.3 4x4) with approx 8500 miles on it seems to hesitate a tad bit mid range in second gear when I floor it.

    Has anyone else experienced this?

    This past weekend I put an airaid intake and gibson cat back exhaust system on. I don't remember the Yukon having any problems before the mods. Then again, I never stomped on it. Before I take it to the dealer I though I'd give it a few more weeks.

    Is this the computer adjusting to the mods? Is it temporary? Any suggestions/comments?
  • junglegeorgejunglegeorge Member Posts: 129
    Same filter issue here in upstate NY, the dealer is the only one carrying the PF-48 , my 2003 Tahoe with the same 5.3 used a PF-44, my 2004 Tahoe with the same 5.3 used a PF-46, and now the 2007 uses a PF-48. Seams to be a trend here. The dealer list is just shy of $11 each, I purchased a case (12) for $4.61 each, still higher than they should be.
  • tuscotoddtuscotodd Member Posts: 50
    mobile1 -
    It sure won't hurt to keep an eye on the fan situation, but I can tell you that they do work in traffic. I spent 2 hours going 10 miles yesterday with a trailer and Bobcat in tow (approximately 5000#) and the temp stayed in check without issue. :D
    On the filter situation, I have my local parts guy checking a couple different sources - but so far, he has hit a brick wall on availability. I've bought the last two from the dealer here. (sorry I couldn't be of more help on that one!)
  • jmaynardjmaynard Member Posts: 37
    You might want to try it without the traction control turned on. Sometimes the stabilitrack interfers with the acceleration.
  • eliaselias Member Posts: 2,209
    fuel is indeed shut off while decel/coasting-foot-off-gas, above certain rpm. as for question from 73shark, the engine keeps running when you shift into neutral because then the computer tells fuel-pump to pump a nonzero amount of fuel.
  • eliaselias Member Posts: 2,209
    hey there jmaynard. i am not insulted by you or anyone disagreeing with me. "i get a lot of that."
    your statement about engines is false. an engine can run just fine without fuel and have been doing so for a few decades if not more - they can run without fuel downhill, and/or with foot-of-gas coasting-in-gear-until-certain-low-rpm-is-reached.
    i am only talking about the vehicle being in-gear, foot-off-gas, rpm/speed above certain low threshold.
    there is no "mist" of fuel being injected in this 'deceleration' condition. zero fuel is injected.
    also your final statement about "physical law" is false. an engine will not necessarily stop without fuel, as long as you are coasting-in-gear with foot off gas, the engine will run indefinitely. if the "physical law" you state were indeed a law, every engine would seize up when the fuel supply ran dry! ouch!
    regarding your final case about "something" providing energy to make the crankshaft turn - YES - it is the kinetic energy of the vehicle which is being converted into energy turning the crankshaft. as long as the downhill is steep enough, this state can continue indefinitely.
    in the flat-road case, this zero-fuel-used condition will only last until the vehicle decelerates down to some low rpm & speed. when the rpm drops all the way to idle-speed, by then is when the fuel pump starts pumping a nonzero amount of fuel.
    hook up a diacom/OBD3-laptop to your truck and you can see for yourself (preferably while someone else is doing the driving/coasting-in-gear-decelerating-or-going-down-long-hill)
  • tuscotoddtuscotodd Member Posts: 50
    Hmmm - I find this rather interesting. I can only offer my observation to this, but here it is. On the zero fuel issue - if they are doing this with the newer fuel injection systems I think that is great! But I can confirm without a double that at least the throttle body versions used in the 90's did not go to zero fuel during coast deceleration, as I spent time working on both my van and my parent's van (with the cowl cover off) and can tell you that the only time that it did not inject fuel is when the key was off. Maybe this is something that changed with common rail and sequential injection but it definitely wasn't the technology applied in the early 90's on the throttle body injected G-20 and Astro vans.
    As to the zero fuel during coast, I know that at least with my '07, the initial let off of the gas does not generate any engine braking (it takes 10+ seconds of coasting before any engine braking starts), so I doubt that it is going to zero fuel, at least initially, during this condition as otherwise heavy engine braking would start immediately?
    One other thing to note on thezero fuel situation, and possibly this is being worked around with the use of the lock-up torque convertor, is without the engine driving the pump in the front of the transmission, the tranmission would be provided no lubrication and would loss line pressure resulting in the disengagement of the clutches holding the transmission in a particular gear. (this is the reason that you can't pull/push start an automatic) Now as I mentioned, it may be possible that this is being circumvented through forcing the torque convertor to remain locked up?
    Just some food for thought.
  • jmaynardjmaynard Member Posts: 37
    elias obviously has no idea how the internal combustion engine works. Gasoline and deisel engines do not run without fuel. ONce the fuel supply stops, the engine stops. Even when the vehicle is coasting fuel is being delivered to the engine and the engine remains running. Tuscotodd's comments are right on track. The torque converter in an automatic transmission does not lock when coasting in order to turn the crank on the engine. This action would reslut in damaging the shaft and the pistons and lifters. In order for te engine to remain lubricated, it must run. If it stops, so does the oil pump. In addition, the ac compressor is turned by the engine. If the engine stops, so does the AC. And last, but certainly not least, watch the RPM gauge when you are coasting. If the engine were stoppped you would experience 0 rpm's. Now, you may say that the 'computer' still shows rpms's becuase the engine is still turning due to this ficticious torque converter lock. To rebutt this, one must inderstand where the reading for the RPM gauge comes from. This device 'reads' the spark generated to the plugs. It the engine is not running, no spark is required, and no RPM's will appear. If you want to test this. put your car in neutral with the key turned on and roll down a hill. No RPM's, see.

    I have family members that have been in the auto repair business for over 80 years and, elias, you are dead wrong on this one.
  • jerrywimerjerrywimer Member Posts: 588
    I'll have to agree with you here. Either it's zero, or else a very small amount of fuel during the conditions you describe. I've actually done something that more or less proves this to be the case:

    I have a steep section of interstate grade I travel to and from work daily. Coming home I travel down this grade. With the 2004 Silverado I noticed that if I leave the engine running and in drive, the truck maintained close to 2000 rpms on the downgrade at roughly 60-65 mph. Knowing that the 5.3l idled at ~600 rpm, I figured that the truck would be more efficient if I put it in neutral on the downhill section. I watched the instant mpg readout on the DIC for two different trips and the truck actually reported (MUCH) higher estimated instantaneous readings for the trip in gear than the downhill run out of gear. Both runs were during different tanks of gas, so I had manually calculated averages to back up the experience. At the very least, less fuel is injected into the cylinders when coasting foot-off-throttle than is injected at normal idle despite the more than 3x RPMs.

    junglegeorge- On the PF48 fuel filter thing- the 07 Av takes the same filter. Same situation. I even suspected that maybe the filter from the 06 TB 5.3 might fit (it is also an AFM truck engine). It might, but the part numbers don't match. At the current time the dealership has a monopoly on filters for our 2007 SUVs. One other note about it- I'm not sure who quoted you ~$11 for the filter. I bought mine from a local Chevy parts department for just over $6. The bulk price you got still sounds better though.
  • rockman59rockman59 Member 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 Member 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 Member 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 Member 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 Member 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 Member 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
  • tony20fantony20fan Member Posts: 30
    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:
  • muskyhuntermuskyhunter Member Posts: 9
    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.
  • junglegeorgejunglegeorge Member Posts: 129
    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
  • tuscotoddtuscotodd Member Posts: 50
    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 Member Posts: 2,209
    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 Member 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 Member 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.
  • sovereignmgmtsovereignmgmt Member Posts: 30
    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 Member Posts: 20
    WHO CARES!!!!!!!! you guys are arguing over nothing. Move on. :sick:
  • fundadfundad Member 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 Member 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 Member 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 Guest Posts: 52,454
    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!
  • jerrywimerjerrywimer Member Posts: 588
    Thanks for the link steve. I'll refrain from further discussion of this topic here.
  • steverstever Guest Posts: 52,454
    I suspect there's a bunch of info (and debate) over in the hypermileage threads too in the Hybrid Vehicles board.
  • jmaynardjmaynard Member 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 Member Posts: 37
    Sorry for the typos. Small laptop keyboards and large fat fingers don't mix.
  • 73shark73shark Member 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 Member 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 Member 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 Member 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 Member 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 Member 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 Member 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:
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