Decreased fuel economy on LBZ

Recently I have encountered a pretty significant decrease in fuel economy with my LBZ. Unloaded in warmer weather, I was averaging ~20mpg and getting ~650 miles out of a 34 gallon tank. My last tank, the 'feed me' light came on with only about 490 miles on the tank (~14mpg). No current DTC's, no abnormal noises, it still runs great. I did throw a code in November (fuel pressure related) and the truck limped for about a mile before I got it home and changed out the fuel filter. After installing the new filter, I reset the DTC and the decreased fuel economy seems to have followed... but it's been pretty cold since the filter change as well.

Is it likely the recent cold weather we've had is the culprit? Winter blend fuel? I recall a bit of a decrease in fuel economy last winter but don't remember it being so much. I do have the grille cover installed.

For what it's worth, I seem to notice a slight decrease in engine power since the filter change in November. I had been running WIX 33910 fuel filters but changed to a Baldwin BF7827 this time around.

Hmmm...winter blend fuel and cold weather will really sap your mileage expectations. Not sure how a new filter could hurt mileage...have heard the opposite - that the last tankful before a filter change was the best mileage...

Are you certain of the 20mpg 'averages'? If so, that is the highest I've heard from anyone with an LBZ, who seem to fall somewhere in the 16-17mpg range for empty mixed duty.

How is your air filter? They can become road-salt encrusted and really block flow, even though they still look good.

I don't recall if I ever broke 20mpg but I know I was in the 19's for a while with the truck in the summer but a lot of that was on flat a 2-lane highway stretch with a 55mph limit that gets enforced pretty heavily.

Your take on the fuel filter sounds about right - my observation of the fuel economy decrease was probably more of a coincidence than anything else, but I thought I'd throw it out there.

Since the November fuel filter change I have only run about a tank & a half through the truck driving back & forth deer hunting; it's a drive to get to my spot & back and it's mostly highway so the engine has plenty of time to warm up to operating temps.

Take it out on the highway on a level stretch (as level as possible, not in the mountains) and lock the cruise control at 60 or 65. Reset the average mileage on the DIC and run it for 10 miles or so. If you get better than 20 at 65 you're doing good....

Our"s seems to get less mpg in the really cold months. I think part of it is the winter blend fuel.

Are these fuel mileage figures hand calculated or straight off the trucks readouts? I had an 04' that game me all kinds of weird numbers on the dash, but hand calulated, the MPG's were horrible (gasser pulling a 5th wheel).

I always run better mpg's in the summer, never noticed before/after fuel filter change. Winter with more idling. I average 16 in the winter which is rarely loaded or pulling, and 18 in the summer unloaded. Last summer I hauled our boat (20') out of Illinois back to central Iowa, mostly flat I-80, 70mph constant speeds and average 21 mpg. That was a great day for my 01'!!!

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Originally Posted by Shed

Are these fuel mileage figures hand calculated or straight off the trucks readouts?

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I don't have the fancy telemetry on my `06 that some guys do - all my fuel economy figures are hand calculated... miles logged divided by # gallons at the next fill-up.

What really caught my attention was that I didn't break 500 miles on the last 34 gallon tank whereas I usually approach or exceed 650.

Hand calculated is always the most accurate.

When filling, if at different stations, you can skew the averages on single tankful calculations based on truck sitting on a slope away from pump, vs. slope towards truck.

Most meaningful average will be over multiple tankfuls. I would recommend zeroing your trip odometer at the next fillup, and keep your receipts until you have driven 1500 miles or more...

The winter blend fuel is factor #1. The cold robbing heat from underhood is factor #2. Rolling resistance in cold (diffs, tires, etc.) is #3.