Even if your tires are seriously deflated, that's not going to be the root cause of your issue... sounds like a vacuum leak issue to me and it seems like you're on the way to figuring it out in your other thread...

 

City rating is ~10mpg for these tanks running bone stock, so although 7.5mpg is pretty crappy, it's not that far off, and it sounds like you have a lot of additional weight on your truck. Have you considered unloading all your gear/roofrack and repeating the consumption test before dropping $2-3k in SAI, cats and tires?

 

2hrs of idling per day? You still pulling a Matt Foley? To figure mpg is easy. You just want to do it the same way every time .
I'll start by filling my tank till it clicks off. Then I squeeze the fill lever till it clicks off a second time, now I'm done.
Then I reset my tripometer and drive until the fuel light comes on. Fill up until it clicks twice. No squeezing in as much as you can or rounding up. When it clicks off that second time thats it. Divide the miles on the tripometer by the exact gallons you just put in. There's your mpg. Write it down or use an app to track it.

 

This big girl loaded to the gills with probably 1000 pounds inside the truck, pulling the 110 on a dolly loaded with another 1000 pounds of junk inside, through the mountains going from Chicago to Augusta averaged 10.5 mpg I was doing 65-70 mph when I could. Going up the mountains that old girl was in 2nd or 3rd churning out all the RPM the 5.4 could give.

Normal day to day commute is about 12.5 mpg. I have a fuel leak under the hood somewhere I'm chasing as well so hopefully that will improve.








I'm not sure the worn tires are going to really make any drastic change. Unless you go to a less agressive tread, harder compound with lower rolling resistance. Getting the engine running right will be the big part. I would figure out those SAI issues before I spend all that money on cats.

I really have to believe all those codes are hurting your economy along with all the idling. When I had misfire codes I was loosing 2-3 mpg.

 

Noo no 2 hours worth of idling total since last fill up. 15 minutes one morning, 30 minutes another morning etc. I only mention the cats because back when I was sorting out the misfires and flashing check engine light, the cats were glowing red. Furthermore when the inspection station hooked up their computer to my truck they found a code that suggested dead or inefficient catalytic converters (forgot the description on the paperwork). I replaced the plugs, wires and coils before the cats stopped glowing red and no more flashing check engine light. Most all my codes only resurface after idling so I assume the misfire issue has been resolved but the cats are toast and possibly effecting my MPG.

Im sorting out the SAI first as stated above and will have a new hose and pump shortly. Hard to believe that a leak in the SAI can cause so much havoc. Will update when the new pump is installed.

 

Depends on the fuel station. Last time I tried pumping more gas after the first click I had fuel spewing out and down the side of my truck...

 

As an update I downloaded a mph/kph app free from apple and went out on the highway to see just how fast or slow I'm going compared to what the speedo and UG are reading.

The verdict is when the speedo tells me 60 the app tells me 62 and the UG tells me 55. on the stopwatch side using mile markers I did one mile in 57 seconds while the speedo said 60 the whole mile. at that same time the odometer read .9 rather than one mile!!

So My odometer is around a tenth off which explains why 335 miles turned into 297.

I think I'm going to believe the app which is closer to the speedo now than before with the stock size tires.

The UG is still 5mph lower then the speedo regardless.

 

Alright so I ordered the parts for the SAI system and will install them as soon as they are delivered. Next question: what is the average MPG highway I should expect from my D2 assuming I address the current issues and taking into account all the gear/accessories and extra weight on my D2? Factory specs are 12 city and 16 highway.

 

I've made the return trip across the state and have a little more to update...

I checked google maps and found my trip is actually 320 miles point to point... So with stock tires the Odometer was wrong on the high side reading 335. With the 265/75R16's it is low reading 297 miles.

The upshot, my MPG readings even using the old method of filling, driving, filling again and doing math, were never correct because I was using the odometer which was wrong with both sets of tires. The only thing you really know accurately is the amount of gas you used (and that assumes the pump is correctly calibrated!!) The only accurate way to get mpg data is to look up the exact miles, not what is on your trip meter or odometer. If the Odometer is off by 30 miles on a 300 mile trip, that is a 10% error introduced into your math.

To TriarII i'd just guess you should be getting 10/12 at best with your setup.

My takeaway is that if you are this worried about your exact mpg you should not be a Land Rover owner. :-)

It is literally the cost of the cool factor. It is what it is and you can't worry about it unless like the original poster something is mechanically wrong and you need to spend even more money to get it right.

Land Rover ownership and continued spending money go hand in hand. I'm just glad fuel prices are still relatively cheap.

FWIW i believe I am getting around 14.5 highway now with these tires, unloaded, stock bumpers, and correctly calculating how many miles were driven rather than relying on the odometer.

I was previously calculating 15.5 but that was using the odometer which was telling me i was traveling more miles than actual (old stock tires.)

 

Thanks for the feedback however you misunderstand the thought/purpose behind my inquiries. As a daily driver Im not concerned with the fuel economy of my D2, so long as its getting the average expected fuel economy as intended. Fuel economy only matters to me when Im prepping for a cross country road trip. Its my responsibility to do all the homework, figure out the total costs associated with the trip, how much $$$$ for gas, when and where to fill up etc. These MPG figures help me plan my route and also dictates how much $$$$ I need to put aside. Follow me?

I also find myself increasing frustrated/skeptical of GPS devices as they have proven very unreliable, inaccurate, slow or just cant find your POI's. Bought my first map/s and have been studying them and manually figuring out where fuel stations and other POI are located. Knowing my fuel range and average MPG is critical in route planning.

PS: Tom Tom GPS units are ridiculous and absurd.