Fuel Economy Drop

[bigbrother44]

Since July, my '02 7.3L Excursion 4x4 has been steadily dropping mpg's. A few things have changed during that time that I was blaming it on, but I think it's something more. I just have no idea where to start.

Previously, I was getting 13-14 mpg around town and as much as 17.5 on highway trips. Of course my 16 year old son that started driving it quite a bit in July is not going to do that well, but he's gone from 13 around town to 11. The last highway trip in August I got just under 16 mpg, and this weekend I BABIED it for 311 miles and only got 14.86 mpg. All mileage is hand calculated.

The mileage was slipping a little prior to August, but I lifted it and installed wider tires, so I thought that was the cause. This summer I replaced the used tires I put on when I lifted it with new Cooper Discoverer's. They seem good, but the mileage is still dropping. I did notice a small amount of fluid flung from the pinyon seal, but I read the forums here and came to the conclusion that it's not something to worry about unless it's really leaking. The brakes seem fine, and aren't making any noise driving or stopping. There is a VERY light vibration at 70 mph on the freeway, but I only even notice it when I'm really looking. I'm not hearing any unusual noises either.

I had the oil changed at the dealer in July, supposedly they used Motorcraft oil. That was about 3500 miles ago so I pulled the dipstick. It's good and black as expected, but only 1/2 way down. On my 07 6.0 F250, I would lose about 1 mpg toward the end of the oil change, but never this much.

Ideas???

Thanks!

 

[BIG JOE]

How many miles on the X ?

Air and Fuel filter changed lately ?

Try filling it up at a half'a tank ? (air in the fuel issues @ below half full)

R&R the inlet fitting on the fuel pump.. with a section of fuel hose, vice the QD fitting ? (again, air in the fuel issues)

Joe

 

[bigbrother44]

Thanks for the response, the Ex has 179,000 miles. It has a K&N air filter that I cleaned less than 5,000 miles ago. I will have to check on the fuel filter, I don't remember. I get the air filter, I should pull that and check it though the meter/gauge says it's good. The fuel filter being clogged though, hadn't thought of that dropping fuel mileage. I should look into that anyway.

 

[A/Ox4]

To address your fuel economy concerns, I suggest you investigate boost leaks. Those are a very common cause, and easilly fixed.

Fixing boost leaks with commercial solutions --> http://www.youtube.com/watch?v=KW0yHX_KBr8
Hot to build a leak detector --> http://www.youtube.com/watch?v=Z3HmH86CCXE

Other than that, everything is just maintenance. Check (and if necessary change) fluids and filters. But my money is on the boost leaks. They creep up on everyone. Really it should be added to everyones' regular maintenance check list.

Here is a thread by me from another site on MPG loss.. http://www.ford-trucks.com/forums/1083802-places-to-look-for-cause-of-low-mpgs.html

As an anecdote, I would look into replacing the K&N with something else. Its not a super urgent thing, but I would make it something to look into. Perhaps a 6637 or something easy right now. I recommend the AIS if you dont have wishes of high horsepower.

There is evidence to suggest K&Ns are bad for turbochargers. The reason being is they flow more than they filter. All filters have to balance flow against filtering. K&N has roots in racing, and in racing, flow beats filtration. Unfortunately this is not the case when you have a turbocharger. Flow is of course important, but letting too much dirt by can damage the turbo wheel, this is termed "dusting". Some people dont believe that K&N is to blame, and to be fair, okay, the evidence isnt concrete, but it does suggest this. But if its possible that K&Ns might do this, I choose another filter.

Below is an image of a severely dusted turbo. Unfortunately the forum this picture is from wont load due to a malware alert, so I cant report exactly what the problem was in this case.



SORRY FOR THE SIDE BAR!

Once you check for boost leaks let us know what you find and we can go from there.

 

[DaveBen]

Several of us, including me, have been stating the misinformation on K&N for years. I suggest AIS as a filter replacement for stock. Thank you Trey.

Dave

 

[JRJ04]

To address your fuel economy concerns, I suggest you investigate boost leaks. Those are a very common cause, and easilly fixed.

Further to Trey's point...have you noticed any power loss at all? If the leak(s) are bad enough, you'll notice a significant power loss.

I would also check your fuel pressure. You'd be amazed at how the improper fuel pressure can affect the way a 7.3 runs. A lot of times, the o-ring on the brass sleeve that fits inside the regulator can be bad...thus bleeding off much needed fuel pressure.

 

[Hansel]

Since the age of the truck look into also seeing if the fuel pick up and those 2 filters are good, my truck has over 250,000 miles and I just had the filter pick up replaced because it was broke and the filters where clogged. Boy the truck has better power and is running really good, its amazing how a slow process of those filters clogging up over the years you don't notice it.

 

[bigbrother44]

Now that you mention it, the power has been disappointing. I had been chalking it up to being used to higher horsepower vehicles that I've been driving, like the 6.0 pickup the Excursion replaced, and other newer vehicles I've been driving for work. I will have to find time to check the turbo as suggested.

I inspected the air filter/box last night. It hasn't been very long since I washed the K&N filter, but it was dirty again so I blew it out. It wasn't dirty enough to be causing any significant problems though, it was MUCH worse when I first bought the truck and was getting 17 mpg highway. But I did notice that the plastic lip for the front side clip that holds the filter box closed is missing, so the filter box is only being held closed by the back clip. I don't know if the local Ford dealer broke it during the last oil change or if it spontaneously snapped from age. But I'm going to have to find a solution for that. I agree with the K&N statements above, the truck came with it so I've been using it. I guess I'll be digging around to see if there is a higher-flow replacement filter/box system. Anyone know if the 6.0 air filter and box will fit in the 7.3L engine compartment? It seemed like a much better setup.

 

[JRJ04]

Not sure on the 6.0 filter setup being retro-fitted to the 7.3, but one very popular option that is pretty inexpensive is to go with the NAPA 6637 air filter. You basically remove the entire airbox, get a small piece of 4" pipe and a few clamps and set it all up. that will provide a TON more air flow than the drop in K&N. Do a search in our wiki section for a writeup on this. I had this setup on my truck for years and LOVED it.

Note that if you go with the 6637, you'll hear the turbo A LOT more. Some people like this...others don't. If you're not a fan of more noise but still want good airflow and filtration, i would go with the Ford AIS Severe Duty Intake. Flows a lot more air than stock, but still fairly quiet.

On a side note...chances are the dealer didnt break the clamp on the box. I had a drop in K&N very briefly and the rubber seal on it was significantly thicker than the factory one. It caused my factory air box to "stretch" and one of my clamps acutally broke...thus the reason i ended up with the 6637 setup.

 

[bigbrother44]

Finally got the backsplash up in the wife's kitchen, and am prying my Excursion out from under my 16 year-old's butt tomorrow (he hates driving the wife's car, just like me!).

I checked the records that came with the truck...it's been about 25,000 miles since the last documented fuel filter. So in the morning I'm gonna hit Napa, change the filter, then fill up. I run Chevron diesel from a station that has a decent product turnover, but I'm thinking I might run some cleaner through it this tank, just for the heck of it.