Ok guys here we are again. 04 6.0 new hpop. New fuel filters fresh oil change. I put hotshots diesel extreme in the fuel and Stockton eliminator in the oil. Non studded and no issues with the truck what so every except the poor mileage. I have the looney tune which is supposedly made for improved fuel mileage. I drive 95% of the time in the city. Don't really have a heavy foot. 25 gallon tank and on my best tank I get 275 miles per tank. Most of the time 250 miles. So basically 10mpg. What's the deal? I've checked the front drive shaft. It does spin freely so I know I'm not locked in 4wd killing mileage. Any other suggestions?

 

First thing to check is for sticking brakes very common and is your truck actually getting up temp over 185° not just in the middle of the useless dash gauge. Do you have a gauge that reads live data your going to need it. Form that fuel mileage you've got something going on for sure my lifted v10 is beating you in the mileage department and that's not saying much I'd also return it to stock tuning and see if you have any changes. Ive got more but let's start with the basics and I'm sure rest of the crew will be along soon to help

 

I was using a edge cts insight but recently sold it and went back to using an android phone and dash command. I run around 200 degrees give or take on both oil and coolant. No codes other than egr which is deleted. Not positive how to check on the brakes other than jack it up and spin the wheels manually? Truck will cruise normally meaning it doesn't pull to one side or slow unusually fast

 

Great advice to unload the tune. Troubleshooting is hard with aftermarket mods.

Having just had a sticking caliper, you can tell by the heat of the rotor, or the smell when things get hot enough. As you mentioned, jacking it up and spinning the wheels is good test also. A sticking rear caliper probably won't be very noticeable when it comes to pulling to one side.

Then make sure your tire pressure is where it should be.

Then check for a dragging belt due to a stuck pulley or air conditioning compressor.

If you still have a functional EGR system, pull the EGR valve and inspect.

Check for boost air leaks and check the filter minder to ensure you are not driving w/ a restricted air filter.

Have the engine scanned for codes. Verify that MAP and EBP sensors are plugged in.

Verify that EBP, MAP, and Baro are all within 0.5 psi of each other at KOEO. Verify that IAT1, IAT2, TFT, EOT, and ECT are within a degree or two of each other after an extended "cold soak" period (12 hours wit engine off).

No doubt your fuel economy is low, but IMO you need actual hand calculations of fuel economy (miles driven divided by gallons put into tank - not tank volume) - making sure the tank is filled as completely as possible. Unless the tank is harpooned (modded to eliminate the vent tube back pressure), it can be hard to fill the tank to the same level every time. That is why you need multiple data points.

City driving w/ heavy A/C operation and the looney tune means 12-14 mpg at most IMO. 275 miles on say 23 gallons puts you at almost 12 mpg - not way off. That's why multiple hand calculations are important.

Quick questions - seeing any excess smoke? At idle? During accelerations? When you do get it out on the highway, what boost can you get it up to on a spirited acceleration?

 

Is this a new problem or the way its always been? Are you running larger than factory tires and if so is the speedo recalibrated for the larger tires?

 

run 75-80 psi in the tires. drive with a light foot and coast a lot.. i get about 10 mpg in the city but i dont TRY and get good mileage

 

I'm having the same problem. I run Gearhead SRL tune when not towing and was getting 14 - 17 highway. Now it's dropped to 10. I'm going to do some pencil and paper calcs, but it's got me puzzled. How much boost should I see on "spirited acceleration"?

 

Mark had mentioned air restrictions above, but one I stumbled on that increased my mileage:

There was a thread about a guy putting a late model front end on his Ex -- he asked what this flap was in front of the main air horn on the front of the stock air filter. So I went out and looked at mine because I was sure my horn came through the flap next to the cooling stack.

Well, yes there was a hole in the flap, but the horn opening was about 1/3 covered by the flap, in other words it was supposed to come THROUGH that hole. I fixed that and my mileage improved, enough that I noticed like between 1 - 2 mpgs...

Sometimes it is the little things...

Good luck with finding your issue(s)

Scott

 

Just recently fueled with higher Cetain fuel, made a huge difference , I do run a Diesel kleen Cetain boost every fill but this propel fuels sold at Shell station made me a believer , ohh 19 to 22 mpg , 16 to 19 on regular truck stop fuel, around town blaaa 10 to 14 mpg , I stay on the open road better for the wallet and less lights to stop at .
As Mark has posted Maf , Iat2 , map, EBP and EGR valve could use some cleaning up , also stay with the factory air filter ,and only use maf cleaner for the Maf.

 

How about getting on the highway, try about 100 miles of steady driving. Fill up again and check mileage?
City driving has so many variables.

 

The boost you have on an acceleration depends on the tuning and the turbo you have. I get to 22-24 psi boost w/ the SRL+ tune and stock turbo.

Another factors - tires. Going to mud terrain tires cost me 1.5 mpg. I definitely see it if I don't keep them aired up (I run 75-80 psi in them as well).

City driving eats me up as FL SuperDuty, 04badford, and xcrsp440 mentioned. I get around 12 mpg city driving and around 17-18 mpg on the highway. For highway driving, the wind is a huge factor also.

A friend w/ 250k miles on his 06 just picked up 2 mpg w/ a new set of injectors - everything else the same.

 

You guys are awesome with the responses and info. Everything you've mentioned I've checked out or have done. I'm now at 12mpg. Just ran a full 25 gallon tank empty to make sure. I've seen people saying they get 20mpg city with a dually. Do I need to change my tune or what? When I run stock I still sit right at about 10.5 mpg

 

Some people have seen Bigfoot and UFOs...... I'm rocking pretty much the same 15.5mpg avg I've been getting for the last 112k miles. Maybe it all just balanced out, +1 from the FICm tune, -1 from the Ranch Hand, +1 from the EGR, -1 from M/Ts, +1 from going back to smaller tires, -1 for the engine getting older. IDK.

I have a laundry list of small things to do like replace the MAP hose, check the EPB tube, a turbo wheel to drop in, a tune that I've been meaning to order from Innovative for over a year now (Eric has been a very, very patient person), I'm just not all hyped up on it because the truck is running fine and doing what it's always done.

Back in the day of $5 diesel and a 100% city 7 mile commute I was getting 325 miles a tank, it religiously took 27 gallons until the pump clicked off if I filled up on the light. 31.5" A/T tires, and I wasn't really hitting it hard at the lights. I could see 275 a tank with a heavy power tune. It's not as fun, but maybe check out the Eco tune from Innovative.

 

I missed the Dually part, I would think dragging two extra wheels would take mph down a bit .

 

One of my pet peeves is when people say they ran a tank empty to check the mileage. Really? You ran out of fuel on your truck, called a tow truck, refueled and somehow got it started again just to see what your mpg was? That's not how to calculate mileage. Here's how to calculate mileage, and it's the only way.
First you must determine your odometer error. We all have one. Doesn't matter what your speed says, it's only the odometer reading we are after. Don't assume the error in speedo is the same for odo. They sometimes are wacky.

Use gps app on your phone and set it to tell you distance driven.
Record odometer trip meter miles and actual gps miles.
Divide odometer miles by actual gps miles. This is the percentage that your odometer is reading. If it's less than 1 you likely have oversize tires.
Subtract that number from 100. This is your percentage of error.
Multiply the error by your next "tank" odometer reading. Then add that back to the odo reading. This is your actual miles driven.
Divide by gallons used. This is your MPG.

So, for me with 35" tires I take my miles indicated, let's say 10 miles on trip meter while using my gps which indicates I actually travelled 10.8. That comes to .926. Subtract from 100 and you'll get .074. Or, 7.4% odo error. Now keep that handy for the next few tanks of fuel. Odo reads 325x.074= 24.05 miles error. Combine to tank and see that we actually went 349.05 miles. Divide by fuel pumped back in to top, and we get 13.96 mpg.
There might be different ways to use the same math, or maybe a shortcut here and there but that's the way to do it, as accurately as is practical.

You need to do it over several tanks, because city vs hiway, wind, mountains, or truck loads will skew results.