8 mpg City, no mods except tires...something's gotta be off

[RobRed]

The ECU would re-learn over several fuel fill-ups the new driving habit.

I would always suspect something mechanical in these cases... The thermostat (via FJ forum) is an interesting fix and the logic is sound - it obviously worked for that poster. My thought initially is that there is some type of vacuum leak or exhaust issue causing the drop.

By the way if anyone is a member over there (Fj Forum) they should remind PocanoPAFJ to talk to toyota corp and have them replace the cats - burning fuel off in the cats destroys the substrate.

 

[LCbruiser2000]

Hadn't heard any of that stuff about the tstat before, interesting. I will agree that 02 sensors can affect fuel mileage long before they throw a code, but it isn't a guaranteed fix. I average 13mpg with no running boards or sliders, an ARB bumper and 305s. It just depends on your particular truck. Some are pigs, some aren't.

That's why products like the tornado still get sold.

i guess mines a pig with no extra weight!
haha
oinkety oink

 

[LCbruiser2000]

what about resetting the ECU to see if that changes anything? wouldn't it be possible that after resetting, it might throw a code that isn't showing up in its current state? i also thought the ECU "remembers" your driving style and makes adjustments to engine performance based on your average driving over a certain period of time/distance. perhaps this rig was driven like a race car in the past and it just wants to dump fuel every time you drive it? i'm just guessing here...but under 65k it shouldn't have any issues unless its something related to sitting around for a while, 'cuz that's some low mileage.

if i had the mechanics reset the ECU, will that cause me any problems? or is it comparable to just re-booting a system and everything goes back the way it was....

???

 

[CappyKD]

if i had the mechanics reset the ECU, will that cause me any problems? or is it comparable to just re-booting a system and everything goes back the way it was....

???

It's like rebooting, only the ECU 'learns' idle and fuel trim again. You don't need a mechanic to reset it, just pull your negative battery cable for 10 minutes or so, then re-install. Once you restart the truck, let it sit and learn Idle for 15 minutes or so. So just start it, and don't touch the accelerator for 15 minutes. Make sure that the AC is off when you first start it also.

G/L

 

[KlausVanWinkle]

Buy a Scangauge II

I bought one of these when I had a civic and gas prices went up close to $5 a gallon. Improved my mileage from 28 to averaging 34.

Clean your MAFS and then get one of these to monitor your Throttle position, miles per hour, miles per gallon and gallons per minute or engine temp.

You'd be amazed at what a difference knowing what your engine is doing makes. You can also monitor instantaneous engine HP which is interesting.

Now I live in the west side of LA, drive on the dreaded 405 every day and average between 13-16mpg on a 9 mile commute depending on traffic. The highways get clogged and are so stop and go that highway vs city mileage is about the same. Best I've ever gotten was 18mpg driving I95 from NYC to Richmond, VA.

My truck is all stock, 40psi in the tires, 87 octane Costco gas every time, took third row out and pushed crossbars to the back. Usually drive with sunroof open and rear rear windows popped out. Rarely use AC.

These things take awhile to heat up. I get the worst mileage for the first like 8 minutes.

Since these things are so heavy, they have a ton of inertia. Once you're up to 30-50 mph, you can cost for a long time. I cost into stop lights and off of freeways. Just doing that can bring your average for short trips up by a mpg or more.

Goodluck.

 

[LCbruiser2000]

I bought one of these when I had a civic and gas prices went up close to $5 a gallon. Improved my mileage from 28 to averaging 34.

Clean your MAFS and then get one of these to monitor your Throttle position, miles per hour, miles per gallon and gallons per minute or engine temp.

You'd be amazed at what a difference knowing what your engine is doing makes. You can also monitor instantaneous engine HP which is interesting.

Now I live in the west side of LA, drive on the dreaded 405 every day and average between 13-16mpg on a 9 mile commute depending on traffic. The highways get clogged and are so stop and go that highway vs city mileage is about the same. Best I've ever gotten was 18mpg driving I95 from NYC to Richmond, VA.

My truck is all stock, 40psi in the tires, 87 octane Costco gas every time, took third row out and pushed crossbars to the back. Usually drive with sunroof open and rear rear windows popped out. Rarely use AC.

These things take awhile to heat up. I get the worst mileage for the first like 8 minutes.

Since these things are so heavy, they have a ton of inertia. Once you're up to 30-50 mph, you can cost for a long time. I cost into stop lights and off of freeways. Just doing that can bring your average for short trips up by a mpg or more.

Goodluck.

i too do most of my city driving in the west side of LA so i'm right there with ya! i think the inching along with stop and go traffic just kills our gas mileage....i may just have to hunt you down so you can teach me all these things with the scan gauge in person!

 

[ebod]

I am another West L.A.-er.

It seems that the"These things take a while to heat up. I get the worst mileage for the first like 8 minutes" point may be a big part of what's keeping my mileage so crappy. My commute is about 5 miles and it takes only 10-12 minutes in the AM and about 15-20 on the way home. I guess I shouldn't be complaining. Crappy mileage on a short commute is better than increased mileage on a longer commute.

I have to disagree with the intertia/coast for a long time point. I feel like there's a lot of driveline drag in my LC and that I slow down while coasting, even when it's slightly down hill (more drag feeling than our MB GL 450 and way more than my old BMW e30 (which is RWD, not AWD)). Anyone else feel the same way??

 

[OregonLC]

so while I'm not a fan of idle warm-ups this makes me wonder if we'd be dollars ahead by shifting some of the warm-up time to the driveway under idle rather than an enriched mixture under load. six pence or two threes?

 

[re_guderian]

so while I'm not a fan of idle warm-ups this makes me wonder if we'd be dollars ahead by shifting some of the warm-up time to the driveway under idle rather than an enriched mixture under load. six pence or two threes?

Firing up Torque to do some data logging over the next couple of days. Torque is a little off on it's fuel usage stats, both for my Cruiser and my Avalon. I'll have to do some tweaking. I have some old data from my Avalon that clearly shows that warm engines get better MPG than cold, but I never was able to calculate how much fuel I used to warm up the engine. Most of my "warm" trips were after sitting for 5-20 minutes and not cooling back down. Stay tuned...

 

[RPMLX470]

Any check engine lights on? If so, get that checked out first.
Make sure the check engine bulb is working, it illuminates when you key the car up
Run a diagnostic scan, see if they're any pending codes.

If no codes present, all the sensors that control fuel delivery need to be checked out to see how they are reacting and reporting whats going on with the engine: MAF, IAT, ECT, o2 sensors, etc..

If you're up in the SGV, stop by my shop.. I can hook up the scanner and do a quick check. PM me for details.

 

[99toylc]

You may look into your rear/front brakes and make sure they aren't binding as this is going to be harsh on fuel milage...also the emergency brake hardware as they tend to leave the brake engaged part of the way when a little rusty...

 

[bamachem]

I had the same problem. Ended up that the o2 sensor was bad. Changed that out and mileage went back up.

The O2 sensor "functionality" fades over time. The ECU will not trigger a check engine light unitl the sensor is reading outside it's "normal" range. The symptom of a O2 on it's way out is a sudden drop in gas mileage that may or may not come back up.

O2 sensors seem to have a large affect on MPG

Yes they do. It's because the engine reads the O2 output to adjust fuel trim in combination with the MAF. When the MAF is dirty and an O2 is failing, it screws with the fuel trim and you typically run rich, consuming way more fuel than needed.

No idiot lights with bad o2 sensor?

Not until they have a complete failure. There is an acceptable operating range in the ECU for the signal from the O2 sensors. It can be malfunctioning and still be within range. However, the thing that typically ends up triggering the CEL is when the heating element goes out in the O2 sensor. That usually happens long after the sensor has gone wacky with it's output.

Hadn't heard any of that stuff about the tstat before, interesting. I will agree that 02 sensors can affect fuel mileage long before they throw a code, but it isn't a guaranteed fix. I average 13mpg with no running boards or sliders, an ARB bumper and 305s. It just depends on your particular truck. Some are pigs, some aren't.

That's why products like the tornado still get sold.

Also interesting about the thermostat. Not getting up to operating temps can certainly affect mileage and the fuel maps the engine is using. You're dead on with the info on the O2 as well. A mix of city/highway with 305's and extra weight and 13MPG isn't bad. I used to get 15 on the highway and 13/14 around town in the 2000 when running 32's and 33's - no difference really. On the 07 Hundy, I could eek out 18 on the highway with stock sized tires. City was about 16. That's a VVTi in stock form and no aftermarket adders, so not a valid comparison.

 

[re_guderian]

Obviously, since your mileage has dropped suddently, you should pursue the diagnostics suggested in this thread, but for reference, if you're doing short commutes on a cold engine, you need to be realistic (and data driven) about what your expectations and results really are.

The following graph is from my Avalon, which resets it's trip computer every time the key is turned off (used to bug me, but doesn't now). For a tank of gas, I tracked each trip's distance and the "trip" MPG via the computer (it is biased a little high compared to odo/gallons per fill-up, but for the relative comparison of this graph it works ok). I also recorded the starting engine condition, hot/cold. Obviously, on a 17 mile trip to work, even if the engine started cold, it warmed up quickly. This car has an EPA rating (new method) of 19/27 MPG.

Bottom line, if you're doing short jaunts of less than 4-5 miles, you're gonna see way below the EPA city estimate, even more so if your engine is cold. I would assume the curve has a very similar shape for the LC, just shifted downwards a whole bunch. You also need to realize that your per-tank MPG is weighted by the amount of fuel used per individual trip, not the miles driven on a particular trip, and these short trips with poor MPG use more fuel than you might imagine - for example a 4 mile trip starting with a cold engine at 6 MPG just used 3.4% of your 20 gallon fuel supply, the same amount of fuel as a 10 mile highway trip at 15 MPG.

 

[moooooooo]

i'm with RoboRed. It sounds like you've checked a lot of things, but a vacuum leak was what i was gonna suggest along with an air intake (filter) issue. You said you replace the filter. Good.

remember, if you are using more petrol/gasolene than you should it's because the computer has been "told" it needs more petrol.
So your economy goes out of the window.

Thats where you need to look. Everyone has said replace your O2 sensors...that's a start...but like another poster here....reset the ECU.

Disconnect the battery. If you have dual batteries, disconnect both.

Wait awhile, drive it again. Compare notes, then follow some suggestions. It's pointless spending money on the beast if your ECU is doing what it's being told to do, so reset it.

If after all that, your economy is still crap? Then unscrew the whole air intake system and check it. You dont need to be a mechanic to do it.

Inspect everything...is there a mouse in there? (it happens)...open the throttle body butterfly valve shine a torch in there.

Airflow is everything....oh and if you have a snorkel, then you need to pull that apart too.
cheers
peter

EDIT: check the MAF sensor...you can clean it yourself with CRC MAF Cleaner. Just dont physically touch it yourself. It should be nice and shiny silver. If it's black...then spray it until it's silver.

 

[bkgee]

so while I'm not a fan of idle warm-ups this makes me wonder if we'd be dollars ahead by shifting some of the warm-up time to the driveway under idle rather than an enriched mixture under load. six pence or two threes?

Has anyone tried block heaters? I mean anyone living south of ~40 degrees lat? I would think they would be a cheaper way to get the engine up to more efficient temperatures... Not to mention a faster way to get hot air conditioning.

 

[moooooooo]

no offence, and happy to be educated differently, but my LC gets up to temp pretty quickly and the idle RPM is around 700 RPM, ...need to re-check it with the scanguage as it's been a while since i had rpm on there. Mine is a manual V8 though, so that will make a difference.

i'll punch it in later today
cheers
peter

 

[LCbruiser2000]

I will do the battery disconnect today and see what happens. In the mean time I just did 108.5miles (about 9m city, rest hwy) and this is where I'm at on the gas gauge.

Will see what happens after disconnect but I may head into your shop RPM. Just to make sure

 

[OregonLC]

That's not out of line at all for a 1/3 tank. Tracking toward a 330 mile tank full... pretty good in my book!

 

[LCbruiser2000]

That's not out of line at all for a 1/3 tank. Tracking toward a 330 mile tank full... pretty good in my book!

Looks can be deceiving. It'll drop real fast. Even when I fill up - after 15miles it's already falling off "F"

 

[KlausVanWinkle]

I am another West L.A.-er.

I have to disagree with the intertia/coast for a long time point. I feel like there's a lot of driveline drag in my LC and that I slow down while coasting, even when it's slightly down hill (more drag feeling than our MB GL 450 and way more than my old BMW e30 (which is RWD, not AWD)). Anyone else feel the same way??

that's probably true. I'm comparing it's coasting to small cars like my Fiances new Elantra or my past Hondas. Those didn't have a lot of driveline drag but they also weighed less than half as much. Those coasted well at high speed but poorly at slow speed.