Normally when I see threads on DF about RPMs Surging at cruising speed, it's the 06+ Hemi guys with MDS kicking on and off, but as I don't have MDS (or a hemi) that's not my issue...

The symptoms: At cruising speeds, 65+ MPH, my engine RPM will surge +200 revs (most often from 2100 to 2300 rpm) for a second or two, then back to normal. It doesn't matter if the cruise control is on or not, and the PCM isn't throwing any codes. Once this started happening, my gas mileage went to sh*t, dropped by about 35%. I eliminated bad gas as a possibility, since I've drained the tank and it's still happening with fresh gas from a different station. The only thing I could think of is the torque converter locking and unlocking, but I'm hoping there might be a less expensive explanation...

 

didnt no a 4.7 could hit speeds of 65 mph. lol joke lil sis dont get uptight. thats a weird one i hear allot about serging on the mds hemi but never heard it on a 4.7. but i have a friend with a 3.7 ram and his did the same thing , it was a TQ lock up so the dealer said, but like i said i no nothing on smaller engins.

 

you're a mod... your trucks are supposed to be perfect and without problems. what the heck...

i suppose its too small of a difference to be changing from 5th to 4th gear. is it only at that speed/rpms or others too? Whens the last time you ran some fuel injector cleaner through it? sounds like it could be dirty or clogged injectors making the ecu think its getting less fuel, so it just pumps more though occasionally, creating the surge and terrible mpgs. i'd go with the cheap fixes first, like fuel injector cleaner and then possibly seafoam it.

 

Yup.......

 

It's a 45RFE Trans... no 5th gear. Throttle body was cleaned last week and I ran injector cleaner through it about 1,200 miles ago.

 

Are you drive by wire on that truck?
And do the 4.7s have a TPS?

 

That 200 rpm surge at about 65 mph sounds awfully like the TQ lockup doesn't it???
Right revs and right speed.
Does your truck have od lockout?
If so, try it without od on and see if you get the same happening.
Hope this helps?
Al.

 

i agree with al. put it in tow haul or OD off and try it

 

I am on board with the TC lockup, do like Al said and see what happens.

 

Ok - Ive been on this forum -- what -- almost 6 months now?...

Ok it sounds like one of 2 things to me.

One - it could be spark plugs going bad... My Colbalt Twin had this issue with her 05 Balt - and she got it fixed under warranty, so this is something that I know it could be that has NOT been said yet

and the other... is the wiring... Go check them... Bet ya if you go looking for these, ya will find what's wrong...

--Cow-Chick--