I did my 1st mileage check on a 362 mile run to the Pacific coast this week with the 5.4 Screw. With approx. 60 miles of 65-72 mph freeway and the rest at 55-65 on secondary mountain roads plus a few miles of hard-packed beach off-roading in 2nd-3rd gear, the 3.55 ratio turned in 17.15 mpg. For a 5600 pound rig, I was pleased.

With the radio off, the wife/I noted an engine vibe/buzz at 1300-1600 rpm (circa 55 mph) in high gear...noticeable in the steering wheel and floor boards and slightly audible. I eliminated the driveshaft and wheel balance as a source by disengaging the OD and/or shifting to neutral and noting that the buzz quit as rpm increased or dropped while maintaining the same speed. Either the 5.4s primary/secondary balance factors are at play or the engine mounts allow some vibes at the noted rpm.

It's no big deal. It's just that the truck is so quiet that you notice things that would go unheeded in other vehicles.

 

Curious - how many miles were on your truck during the test?

My first test was around the 300-550 mile range. With the 3.73 axle and about 35 miles of 4x4 High (snow conditions) I got 12.82 mpg.

I've got about 800 miles on the truck now, and the motor is getting noticeably looser/more powerful.

 

blitz...I turned 2000 miles on the trip. And yes, my engine is also putting out considerably more power as it breaks in.

I should have noted that my off-road excursion was not in 4X4 (I was saving it for an escape over the dunes in the event of a tidal wave).

 

I'm not tyring to be a smart *** and I'm no mechanic, but how does taking the truck out of overdrive or putting it in neutral eliminate wheel balance as a source of vibration? There is a mechanical link to the wheels through the steering wheel regardless of what the tranny is doing.

 

LOL

 

Because the wheels are still turning at the same speed, while the engine and tranny rpm has varied. If the vibration is still there in neutral that makes a wheel or axle issue more likely because that is the constant.

 

Oops I re-read his post. He said the vibration quit when he put it in neutral. My bad.