Edmunds dealer partner, Bayway Leasing, is now offering transparent lease deals via these forums. Click here to see the latest vehicles!
2007 and newer Chevrolet Tahoe and GMC Yukon
This discussion has been closed.
Popular New Cars
Popular Used Sedans
Popular Used SUVs
Popular Used Pickup Trucks
Popular Used Hatchbacks
Popular Used Minivans
Popular Used Coupes
Popular Used Wagons
Comments
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
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
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.
More in this collection of discussions: Ethanol - E85 FlexFuel
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?
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.
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!)
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)
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.
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.
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.
____________________________________________________________
GM introduced the electric radiator fans in '06 on the Suburbans and I have seen no reports of any overheating problems being mentioned anywhere.
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.
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
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
How is it installed and how easy/difficult is it to do?
Do you like it? Any complaints or praises?
thanks in advance
The wheels look great, by the way. A definite improvement over the dull finish. So easy, now so difficult... :sick:
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 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!
--
TuscoTodd
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)).
Our first US made car in 25 years. So far so ... bad.
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.
Works like a charm! Love it.
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.
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?
Here's the link:
Auto101: How To and How it Works!
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.
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.
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.
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.
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: