RPM RACING WITH CRUISE CONTROL ON - Page 2

joey2cool · 10-18-2011, 01:13 PM

Sheesh. You just broke another myth I always believed cruise control got me better gas mileage. I might have to change my bad habits now.

What you're saying makes perfect sense. The Ford owners manual says to downshift if you notice rapid shifting (i.e., throttle searching). Guessing putting it into overdrive when above 55 mph isn't bad for it, but definitely takes a bite out of the mileage. Sooo, turning off CC sounds like a better option when that happens.

Thanks Mike!

Ford_6L_E350 · 10-18-2011, 07:21 PM

On flat, level ground CC may increase mileage. In hills, even small ones, CC really hurts my mileage.

Going downhill, it lets speed come up - if you're not watching and a radar unit is on that hill. Then, when the next hill starts up, first the speed comes down. After the road is going up, then the speed drops enough for the CC to apply throttle - but the speed has dropped and the road is rising - so it applies alot of throttle (tanking the mileage) causing downshifts to get the speed back up and to maintain the speed.

Driven manually, I watch hills. On the downside I let the speed come up some, but not into ticket territory, and before the road starts back up I apply a little throttle to keep the speed without lowering the mpg's. I watch the MPG reading on my ScanGauge to find a good throttle position. I try to keep the instaneous mileage at or above 10 mpg, even if I have to let the speed fall. On the highway I don't let the speed go below 55. On a series of moderate hills I can keep the mileage the same as on a flat level road. Bigger hills that require more throttle to keep the speed up still drop the mileage, but not nearly as much as CC does.

Mike

Ultrasport12 · 10-19-2011, 02:53 PM

In my 2008 V-10 the cruise is really very steady but that being said it does all kinds of shifting and such to do so. As you go up a hill it will shut off the overdrive as soon as it slows 1/2 MPH and then it keeps shifting down to maintain the speed it is set at.. Going down a hill it also kicks down more and more so it does not speed up over the set speed if at all possible...The normal highway RPMs for me is 2,000 at 70 MPH sometimes going up or down the hills on I-5 it can be as high as 4,000 trying to hold the speed steady and that makes a lot of noise, sometimes you think it will never shift back up but it always does just not as soon as you thing it should. I also think that as the trans and coolant temp goes up while climbing a hill the radiator fan does engage a bit more and that also makes more noise as others have mentioned especially if the RPMs are higher then you hear both the engine and the rad fan noise more.

It is normal for the RPM's to change quite a bit (on hilly roads) with any modern multi speed/overdrive transmission with the cruise control on but in some vehicles it is much more noticeable than others.

When you drive with the cruise off your speed changes more than you think on hills and your right foot controls the shifting (or lack of shifting) much more, and you will get a little better mileage with the cruise off on hilly roads. With the modern E-Throttle type engine control module (the cruise control is built into the ECU with E-Throttle and is not a separate unit anymore) they work together with the transmission control module and the shifting calculations are controlled based upon trying to keep the actual MPH as close to the speed set point as possible thus causing the higher/changing RPMs..

Silver350 · 10-22-2011, 06:50 AM

On the 4 speed, the difference between 3rd & 4th is 740 RPM. (1:1 vs 1:.71). If the RPM change was less than this, I would think it was the Torque Converter unlocking to keep the engine at an RPM were it can provide enough power.

vlamgat · 10-27-2011, 02:07 PM

This thread hits at my pet peeve regarding the CC. Its gain is set to maintain speed no matter what number of shifts it takes and the overall driving experience is quite tiring. Would'nt it be nice if some techie out there could rewrite our control modules so we could allow the throttle applications to be much slower in order to avoid the shift hunting.

regist1 · 10-28-2011, 08:17 AM

Re-gearing my differential has improved this greatly. Even in the Ozarks Hills my cruize works well at holding speed with minimal downshifts.

vlamgat · 10-28-2011, 08:29 AM

What do you mean by re-gearing? Did you change the diff; swap out some of the cogs; where did you source the parts?

Do you tow?

regist1 · 10-28-2011, 08:34 AM

Changed the gears in the rear differential. I pull my 4000lbs Jeep on a 1500lbs trailer, the 5.4L does a good job with that weight. I am 2wd, but have a full conversion inside the EB van.

vlamgat · 10-28-2011, 08:47 AM

What gears did you use? And what was you final drive as a result?

regist1 · 10-28-2011, 12:35 PM

I went from 3.73 with 245/75R16 to 4.1265/75R16 which made the effective ratio at the ground slightly lower then stock gears with the smaller tires. The speedo read about 5% off before I had it corrected.