8.4 to 9.6 miles per gallon

[Amir]

Ever since I have moved here in LA, I have noticed that I have been getting around 170 miles out of per full tank before the warning light comes on. Have had Two full tanks with exactly 170 miles and this time, the third full tank, I got 167 miles. Not sure if this is because of the 91 octane rating. I used to use 93 in the east coast but now I have no choice but it doesn't really matter to me and I seriously doubt that is the reason for low gas mileage. Driving habits have not changed, I am the only driver and and have been driving mostly in the city.

I did have the 7500 miles service at around 6200 miles on the clock when i took the truck for the oil change. At that time the dealer told me that there was a recall or update on the ECU or transmission for better shifting etc. that needed done and they did that. Any ideas. BTW had an amazing time driving from east to west, took some pictures here and there, would like to post, if someone could direct me how to do it.

thanks.

 

[DonA]

As you may already know the government mandated that MTBE cannot be used in gasoline in favor of 10% ethanol. It does make fuel economy slightly worse. But the mileage you describe sounds like it could be a bigger problem I would advise your dealer.

Also when running 10% ethanol the 4.4l V8 seems to have a lean problem on open loop it runs lean & rough until it goes closed loop.

I'm averaging 12mpg in city stop & go

 

[Amir]

thanks DonA. Could you please explain the "lean problem" and the "open" or "closed loops".

 

[nwoods]

Amir, to post photos in this forum, click Post Reply and then scroll down to "Manage Attachements", but the photos need to be prep'd just right for it to work okay. You might have better luck posting to SmugMug.com or something, and just building an online gallery.

My gallery is here:
http://blog.nextstepdesigns.com/?cat=9

I have a V6 LR3, and get about 14 MPG

 

[grommet]

You have something seriously wrong. (Unless you mean you've been "stuck in traffic" the whole tank. The worst I've seen is 9 MPG over the lifetime of my vehicle.) Now, if you do a freeway tank and it's about normal... I doubt you have a real problem.

It has nothing to do with octane. 91 is recommended and 93 has no advantage. Feel free to re-visit the numerous MPG threads for more trend data.

(If your mileage dropped after they performed "ECU" service, it sounds like they broke something!)

 

[kwlr3]

My '05 hse routinely gets 17.5 plus mpg. Occasionally it's bettered 20! It's all to do with where I live (Florida Keys), no hills, high humidity, few traffic lights or stop signs, and it rarely goes above 60 mph. Most tanks are completed at an average speed in the low to mid 20's. A trip to TX was done at about 14.8 to 15 mpg. If I do a lot of short trips aroung town, I see 10 to 11 mpg.

Open loop and Closed loop refer to two engine management conditions. In open loop operation, engine fueling and ignition (and maybe other things like shift points) are detirmined by a stored fuel map. Usually, idle and low load operations would be an open loop condition. In closed loop, engine fueling and ignition timing are detirmined by reading the O2 sensors and the knock sensors. This normally occurs during wide open throtle (WOT) or other high load conditions (towing uphill). My experience has been that lower end cars with cheap fuel injection systems and cars that claim high fuel mileage do so by running more on open loop than closed loop. Trying to supercharge or otherwise extensively modify one of the low end systems is much more dificult.

 

[DonA]

Sorry reread my post tonight it was a little non-descriptive.

When you start your LR3 the engines computer is in open loop mode. A stored set of parameters or "fixed map" for fuel, spark and other functions preset by the engineers.

When the engine is cold it needs a richer mixture (more fuel than air) than normal. Old carbureted engines use a choke for this reason this richer mixture improves cold drivability until the engine warms up.

I have been told that supposedly 10% Ethanol blended gasolines do not require a richer mixture than MTBE did.

I could be wrong here but the fixed maps in cold start open loop seem, to my ear anyway, too lean. I now experience a very rough idle on cold starts after my local station switched to 10% ethanol. I also suspect the computer richens the mixture once it gets control (closed loop) and my mileage suffers. Again, purely my speculation.

Regardless the mileage you are getting seems way too low. Bring it in