Rum, rum, rum@ 3,500 RPM

[DAS26miles]

My E450 with V10 has a slight surging of RPMs at 3,500 and climbiing hills. Normal or something out of balance? New 8 months old 2015 chassis.

[DAS26miles]

I don't see any movement on the tach, but the engine whine at 3,500 RPM has a slight up and down. Not a harmonic vibration. You know how the generator can surge, it's like that but not as much

[dewey02]

Ask Captain Jack Sparrow once said: "What's wrong with a little Rum?"

[DAS26miles]

It' accelerating going up mountain roads when downshifted at 3,500. Scangauge ll has no codes showing.

[tpi]

His "rum rum rum" title to me points to a harmonic vibration rather than a surge. A surge would be an uneven power delivery from the engine-slight change in power output when throttle is steady.

Just from what I read here, I'd say driveshaft vibration.

I will say on mine it has a very slight driveshaft vibration that it passes through at about 62 mph. I am *very* sensitive to driveline vibrations, and I dislike them. However I've chased enough of them to know when to ignore. This can be an expensive wild goose chase that resists solving. In the RV with the long driveshaft, the 4.56 axle which spins them fast, and the coach house box which can set up a harmonic vibration it can be a lost cause if you want pure perfection.

If it is under warranty take it back to Ford and ask them to check it. Maybe yours is so out of kilter they'll do something about it. Don't count on much if it is minor. JD who posted above me always has good useful suggestions.

[old_guy]

am I wrong but isn't surging a result of fuel or electrical problems

[j-d]

Has it been doing this all along? Recently developed/discovered? We don't have a tach on ours, but I'm thinking 3500-RPM is moving right along down the road, 75-mph?
Do you have an extended wheelbase? Look in the door frame and see who stretched it. Give them a call with VIN available. Some stretcher and I forget which one, put a dozen or two back together cockeyed.
Lord Willing, it isn't THAT.
Usual suspects are driveshaft: lubrication, stuck slide spline, angle of differential face, shaft(s) out of balance or mis-aligned.
Mis-aligned can actually BE "aligned!" The driveshaft sections aren't meant to line up perfectly. Slight offsets keep the segmented shaft from vibrating as if it was one long one.
Have you looked to see if something's around the driveshaft, or bent/dented it?
Could of course be a wheel or tire or brake issue. I doubt it's an engine mount.