XC road trip MPG wtf??

[VidRunner]

1450 miles into a xc road trip. Live at 6700' in NM and get ~15 mpg all the time all around the four corners ...

Now in IL at 900' getting 9 mpg.

Had battery discoed all night and had ECU/EFI pulled. Reset all data. Still getting under 10 mpg.

Other than elevation and humidity all variables are the same.

2006 at 202k. Mpgs had been steady for 30k since I bought and modded.

Ideas????


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[VidRunner]

cleaned the MAF sensor ...


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[VidRunner]

also have Ultragauge with the ability to read MAF and O2 values ... not that I know what to look for in those numbers


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[green_manalishi]

I can't help, unfortunately, but I have experienced a similar phenomenon. Last Christmas I drove from home in Denver (5280 ft.) to Michigan (662 ft.). I regularly get 17-18 mpg highway in Denver, but was averaging 12-14 on the entire trip both eastbound and westbound. Mileage returned to normal after returning to Denver.

I've read somewhere that Toyota is very conservative and slow to adapt engine parameters to new environments such as fuel type and driving habits. This is my best guess as to what caused the change in mileage.

 

[VidRunner]

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[BackOff]

Bad gas, parking brake or maybe a stuck caliper. Flat tire. Fail of a wheel bearing. Do the wheels spin freely?

 

[RonJR]

I've read somewhere that Toyota is very conservative and slow to adapt engine parameters to new environments such as fuel type and driving habits. This is my best guess as to what caused the change in mileage.

I doubt that's the issue. The ECU uses memorized values for open loop operation, basically cold engine or hard acceleration. Otherwise the engine runs in closed loop, and the ECU reacts real-time to environmental conditions. It couldn't pass emissions otherwise. It has to maintain the mixture at near stochiometric for the cat converter to work.

Depending on where you are, if you're in the midwest you may be burning E85 gasoline. It's cheap there (government subsidized), but only has about 65-70% of the energy of pure gasoline, so could easily drop your mileage from 15 to 9.

 

[theMayor]

Your cat has gone bad.

 

[VidRunner]

Thanks y'all!
I'd guess gas or cat. Gonna do the temp differential test on it. And swap ASAP either way.


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[BlackWorksInc]

Is this hand calculated fuel mileage or going off the notoriously unreliable computer?

 

[m85476585]

1450 miles into a xc road trip. Live at 6700' in NM and get ~15 mpg all the time all around the four corners ...

Now in IL at 900' getting 9 mpg.

Had battery discoed all night and had ECU/EFI pulled. Reset all data. Still getting under 10 mpg.

Other than elevation and humidity all variables are the same.

2006 at 202k. Mpgs had been steady for 30k since I bought and modded.

Ideas????


Sent from my iPhone using Tapatalk

I can't help, unfortunately, but I have experienced a similar phenomenon. Last Christmas I drove from home in Denver (5280 ft.) to Michigan (662 ft.). I regularly get 17-18 mpg highway in Denver, but was averaging 12-14 on the entire trip both eastbound and westbound. Mileage returned to normal after returning to Denver.

I've read somewhere that Toyota is very conservative and slow to adapt engine parameters to new environments such as fuel type and driving habits. This is my best guess as to what caused the change in mileage.

Part of the problem could be that "regular" gas is usually 85 octane at places above 5,000 feet, but if you run that at lower elevation it's lower than the 87 octane minimum that the engine expects. Since there's less oxygen above 5,000 feet, 85 octane usually works fine, but at lower elevation it can cause problems.

I'm not sure how to correct that, but if you still have more than a little 85 octane in the tank you should fill up with premium. If you've switched to 87 or higher octane and are still having problems then I'm not sure what to do besides resetting the ECU.

I live in Colorado around 5,200 feet, and I've never had a problem with 85 octane at this elevation. My last car was a Honda Civic, and when I accidentally ran 85.5 octane at 1000 feet I got about 22mpg on the highway when I could normally get at least 30.

 

[MrTom]

What blend of gasoline are you using, Regular, E85 or E15?
..

 

[green_manalishi]

I can't speak for OP, but I use regular 85 in Denver. For most of the trip, however, I was running regular 87. If I remember correctly, anything over 10% ethanol needs to be labeled as such at the pump. I was certainly not using e85 (which I'm pretty sure isn't OK in our engines, anyway). My mileage was hand calculated; though this would hardly matter as long as calculations were consistent between home and road.

One thing I did not adjust was tire pressure. Obviously this will decrease as altitude decreases. Though, it would surprise me if that difference accounted for a full 3-5 mpg.

I know that when running in closed loop the engine will run at a stoichiometric ratio. But what I was referring to in my previous post was a rumor that Toyota engines are conservatively slow to adjust timing for new inputs. Perhaps this combined with lower tire pressure could fully account for the increased fuel usage?

 

[m85476585]

There's 15% more air at sea level, so 15% more drag? I don't know if it's that simple.

Atmospheric pressure at sea level is about 14.5psi, and about 12 psi in Denver, so the tires will lose about 2-2.5 psi at sea level. I don't notice much correlation between tire pressure and mileage.

Maybe you have already considered this, but the speed limits on long interstate drives are higher than my normal driving in Colorado. I rarely go over 65mph here, but on cross country drives 75-85mph is common. I usually get about 2mpg less than normal (16 vs 18) in Wyoming where the speed limit is 80, and that's still at high altitude (4,000-6,000 feet, I think).

 

[RonJR]

Speed definitely matters, and the more you have it modded and lifted, the more effect speed will have on mileage. 4runners aren't particularly streamlined in stock configuration, but knobby tires and a 3 inch lift just exacerbates the situation. Add a roof rack with some gear on top and you'll really see mileage drop with speed.

My mostly stock V8 '06 will get 19+ in the mountains at 45-60 mph, but drops to 17 at 75 mph on I-70 in Kansas or Nebraska. Seems like the "wall" for a stock 4runner is around 60-65 mph. I would expect it to be lower for a modded unit.

 

[AuSeeker]

Speed definitely matters, and the more you have it modded and lifted, the more effect speed will have on mileage. 4runners aren't particularly streamlined in stock configuration, but knobby tires and a 3 inch lift just exacerbates the situation. Add a roof rack with some gear on top and you'll really see mileage drop with speed.

My mostly stock V8 '06 will get 19+ in the mountains at 45-60 mph, but drops to 17 at 75 mph on I-70 in Kansas or Nebraska. Seems like the "wall" for a stock 4runner is around 60-65 mph. I would expect it to be lower for a modded unit.

I have the same experience, with my stock 2004 V8, if I go over 65/70 the MPGs drop drastically and I won't even mention what happens at 80 and above!!

 

[94toy22re]

i just got back from Silverthorne, Co. From Silverthorne to Hays Kansas I averaged 22mpg, Hays to Salina had a 17mpg avg and then I ran into a storm from Salina to OKC and averged 12mpg (30 to 40 mph headwind), I had cruise set at 78mph from Denver to Salina! This is with a 2007 V8 with 265/70/17 bfg KO2!

 

[gm350reratliff]

I doubt that's the issue. The ECU uses memorized values for open loop operation, basically cold engine or hard acceleration. Otherwise the engine runs in closed loop, and the ECU reacts real-time to environmental conditions. It couldn't pass emissions otherwise. It has to maintain the mixture at near stochiometric for the cat converter to work.

Depending on where you are, if you're in the midwest you may be burning E85 gasoline. It's cheap there (government subsidized), but only has about 65-70% of the energy of pure gasoline, so could easily drop your mileage from 15 to 9.

OP- are you sure you're not using e85? Could also be that it was mistakenly mixed with regular fuel without you or anyone else knowing. Run that tank out and refill from a different station.

Bad gas, parking brake or maybe a stuck caliper. Flat tire. Fail of a wheel bearing. Do the wheels spin freely?

All of these could be the culprit. I also live in NM and we have driven our 4th gen numerous times to visit family in ND, which is a similar elevation change and we have never had a big MPG change like that unless it's -20F or colder.