Rum, rum, rum@ 3,500 RPM

Home now and NO rum, rum, rum??? Climbed the I-5 Grapevine at 60 mph with the pedal to the metal and T/H on. At the start of the climb RPMs jumped from 3,500 up to 4,700 to 5,100. We stopped at Lebec Rest stop and when we pulled out onto the Hwy I was able to get up to 70mph and hold it all the way to the summit. Maybe the issue was resolved by giving it a good workout. She didn't seemed over taxed at that speed or rpm.

Heading home from Yosemite this morning and will certainly encounter it many times. Will take note and call the local Ford fleet dealer that handled my Winnebago later this afternoon.

What I'd do is try to duplicate it on flat land or convenient hill and once you're able to take it to Ford under warranty. If it is totally RPM related will it do it in park revved up to the noted RPM? These kind of problems are hard to solve remotely.

From what you're writing, it could be an engine surge/misfire, defective torque converter, bad bearing in transmission, fan issue, driveshaft issue, exhaust resonance or contact issue, coach box resonance or mounting issue. The degree of the issue is important. Time to get someone to listen to it. Solving this online will be difficult. Your best effort will be trying to find a way to duplicate it in ordinary locations and circumstances so others can diagnose. You may need to manually hold various gears/RPM and accelerate through the speed range.

And to reemphasize: Big box on E450 will have it's share of noises and other oddities. There is a point where stuff is harmless and can be ignored. Have someone listen to it.

Only on hills when the RPM's increase, how is your air filter and does it have one of those MAP sensors in the air intake,using compressed air to ensure a clean intake may help. Maybe the engine can't breath right and the computer is adjusting for such.

It happens at 35-40 on windy mountain roads and 60-65 mph on hwy mountain roads going over passes just realized always climbing mountains. Maybe elevAtion issue?

Sounds like the engine computer making adjustments under a heavy load to keep ignition, fuel/air ratio within the program parameters.

DAS26miles wrote:
It's not clutch fan, doesn't stutter, not harmonic and weather not a factor. Again its downshifting and climbing hill or accelerating when 3,500 rpm

How fast are you going when this happens? Is speed relevant?

Are you holding the gas pedal steady, or adjusting it somewhat as you drive? I find with my (much older) 4R100 that under these sorts of conditions too quick of an increase in throttle will seemingly cause the torque converter to unlock for a couple of seconds (and hence the RPM rises slightly), even though the transmission has intention of shifting. Perhaps the same applies to the new transmissions, though I would have hoped that bit of programming might have been improved in the meantime.

It's not clutch fan, doesn't stutter, not harmonic and weather not a factor. Again its downshifting and climbing hill or accelerating when 3,500 rpm

Are you hearing the fan clutch engaging? On my pickup(duramax) sounds like a plane taking off.