On a recent long trip I noticed that whilst cruising at a steady 70MPH with the Cruise Control on, the engine revs would sometimes rise by 300RPM for a few seconds then drop agian. It only started doing it after an hour or so and this was on level ground, no hills. On the return trip I suck it at 80 and it didn't do it once (on the same roads) and it hasn't done it since. As you can see its a 2000, 4.7 with the Full-Time 4wd and only 48,000mls. It also had the tranny oil and filters changed less than 8000mls ago. Any ideas?

Thanks,
Paul

 

Clearly the solution is to go faster but seriously could it have been wind?

 

hey I have a 99 dakota 4x4 318. mine does the same thing when you leave it it cruise for a while the engine revs up for a second. I just got my tranny flushed and it still does it. im not too worried about it. mine only does it on a level road. you will just be cruising along between 80-90km it its like its shifting into the same gear.
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N02 vaporizer

 

it may just be the converter unlocking for a second, a slight increase in engine load will unlock the converter when cruising.

 

Thanks for all your help. The one factor I hadn't thought about was wind. Also, going faster might have masked it by putting the revs higher up the power band so the tranny didn't need to change down. It felt like the O/D disconecting then locking up again and so I was worried that it might be the dreaded O/D clutch going AWOL.
Thanks for putting my mind at rest with a couple of possible solutions.

Paul