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Topic: Is this normal for cruise control? (Read 1220 times) previous topic - next topic

Re: Is this normal for cruise control?

Reply #25 –
Dub,

You are good.  Many have driven these things for many years without having the faintest idea what that button/light do.

If you want a primer on using it, let us know. I know I wrote an article for the FMCA Magazine many years ago on the use of the mode button.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Is this normal for cruise control?

Reply #26 –
Primer would be good.
Dub McBride 1996 270

Re: Is this normal for cruise control?

Reply #27 –
Here is a except from the article I wrote back in 2013:



ALLISON TRANSMISSION MODE BUTTON

BY BRETT WOLFE, F252125

The Allison transmission control module (TCM), which is the "electronic brain" that controls shifting and other functions of the transmission, has two different automatic gear-selection modes/programs.

In Economy Mode, the transmission will not downshift even at wide-open throttle until the engine pulls down to peak torque rpm in some applications and 200 rpm lower than Performance Mode in others. In Performance Mode, the transmission will downshift much earlier to maintain higher engine rpm.

Only at higher throttle positions is there any difference, so on flat ground you will not notice any variation between the two modes, except when accelerating from a stop if you are at or close to wide-open throttle.

However, mode selection can make a big difference when traveling over rolling hills. If you drive in such areas while in Performance Mode (particularly with the cruise control on), it is common for the transmission to shift down to fifth gear on the uphill and back to sixth gear on the downhill, repeating this process hundreds of times. In Economy Mode, the transmission will stay in sixth gear unless the hill is so steep or so long that the engine cannot pull it without dropping below peak torque rpm. According to engine manufacturers, the most economical way to climb a hill with a modern turbocharged diesel engine is in a higher gear (lower engine rpm), provided the engine doesn't overheat.

If, while driving in Economy Mode, you know you will need a lower gear because of the steepness of the grade and/or the engine temperature is rising higher than the thermostatically controlled temperature, use the down arrow to drop a gear (this is what I do) or switch out of Economy Mode. Be sure to switch back into Economy Mode when past the steep section or you will be stopping at a service station for fuel sooner than you expected.

While you are driving in hilly terrain, if your engine begins to overheat, the engine's horsepower-to-weight ratio is low, or it irritates you to lose a few mph in the name of saving fuel, by all means drive in Performance Mode.

It confuses me to hear people advocate driving in Economy Mode only on flat ground, as there is not 1 percent difference in shift rpm between Performance and Economy modes on flat ground, except when accelerating from a stop if you use wide-open throttle.

Every time you start the motorhome, the transmission is in Performance Mode. This is the default setting. If you push the mode button, it goes to Economy Mode and the light illuminates.

There is no absolute number that can be given to illustrate the difference in fuel economy that will result when driving in Economy Mode. On flat ground where you will be in sixth gear no matter what mode you are in, there will be zero difference. The most significant difference in mileage will occur in rolling hills, where in Performance Mode, particularly if on cruise control, you will start up a hill in sixth gear, go to wide-open throttle in that gear, and downshift to fifth gear still at wide-open throttle, where it is using a lot more fuel. After the hill is crested, the transmission will upshift to sixth, then likely coast a little in that gear unless you are driving with the exhaust brake on. If you are, the exhaust brake will be applied and the transmission will downshift toward the preselected gear, which is generally either second gear or fourth gear. And so the process will continue, with the transmission shifting up to sixth gear on the downhill, back down to fifth gear on the uphill, etc. The problem with this is that a modern turbocharged diesel engine is much more efficient at low rpm with high throttle settings.

Note: In either mode, you are free to use the up and down arrows to proactively choose the correct gear. You cannot screw anything up, even if you downshift to first gear at 70 mph. The transmission circuitry understands that you want to downshift to the next lower gear as soon as the engine rpm will not exceed the preset amount. Then it will downshift again when safe.

By the same token, you can shift between Performance and Economy modes as often as you want with the transmission in any gear when you make the change.

I drive in Economy Mode 99 percent of the time, including in the mountains. I use the up and down shifting arrows to choose the proper gear. I use Performance Mode only to pass another vehicle on a two-lane road, when I am willing to sacrifice a little fuel economy to gain a short-term burst of speed.

Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Is this normal for cruise control?

Reply #28 –
Very informative.. My mpg has been poor and now I think it will improve. Many thanks..
Dub McBride 1996 270

Re: Is this normal for cruise control?

Reply #29 –
This is the first 6 speed I've had as the 280 had a 4 speed with a shift lever and not many selections. Also had manual leveling that I liked and wish Ft had stayed with but mfg do not stay stuck on just basics that we dinasuars prefer ... there fore the learning curve continues and that isn't necessarily a bad thing.. Good to be friends with people who have been there and done that..
Dub McBride 1996 270

Re: Is this normal for cruise control?

Reply #30 –
Quote from: wolfe10 –
Here is a except from ALLISON TRANSMISSION MODE BUTTON  Every time you start the motorhome, the transmission is in Performance Mode. This is the default setting. If you push the mode button, it goes to Economy Mode and the light illuminates.By the same token, you can shift between Performance and Economy modes as often as you want with the transmission in any gear when you make the change.
I drive in Economy Mode 99 percent of the time, including in the mountains. I use the up and down shifting arrows to choose the proper gear. I use Performance Mode only to pass another vehicle on a two-lane road, when I am willing to sacrifice a little fuel economy to gain a short-term burst of speed. 
Nice article, Brett! I'll bookmark it. I have never used either the 'mode' or up/downshifted. Since most of my driving is  up 7% grades, should I just switch to 'Economy' and leave it there unless a burst is needed? I'd wonder, when to downshift? I notice all my gauges show nothing out of spec. Thanks, M  ^.^d
1993 U-240 "La Villa Grande"..CAT 3116 w/ Pacbrake PRXB...Allison 3060 6-speed..
Previous: 1983 Airstream 310 turbo diesel, 1979 Airstream 280 turbo diesel
                                      Build # 4297
                                      PNW natives
                      Home base:  'Cactus Hug' (Ajo, Arizona)
                        DW Judy & Chet the wonder dog
                        Full-Timers 'Sailing the asphalt sea'

Re: Is this normal for cruise control?

Reply #31 –
Mike,

It takes a reasonable amount of "technical" driving and an appreciation for machinery to know the difference.

Again, no right or wrong ways, but a sensitive, knowledgeable drive CAN do better than "automatic".
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Is this normal for cruise control?

Reply #32 –
To drive manually in 7% grades you need to know the rpm's at peak torque.  Downshift when rpm's fall below that point while at WOT.  Upshift when rpm's approach max rpm for your engine.  Or let the Allison worry about it.
Regards,
Brett

'99 42' Foretravel Xtreme
'14 Brown Motorsports Stacker
'05 Chevy SSR
'02 BMW R1150R

Re: Is this normal for cruise control?

Reply #33 –
Yup, there are some critical numbers every DP owner needs to know for their engine-- call you engine manufacturer with your engine serial number:

Peak torque RPM (don't run below this at high throttle positions)
Peak HP RPM (no reason to run above this RPM under load)
Max RPM no load (important for descent where the engine is OK running at higher speed, since it is not working-- in some cases this is 300 RPM above peak HP!)

Without all these, you can not make wise decisions for technical driving.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Is this normal for cruise control?

Reply #34 –
Reading and learning all the time.
Thanks Brett
Frank & Daisy
NO LONGER  "looking for the perfect Foretravel
36' or less non slide preferred."  She has been found and is ours.
2003 U320 36' non slide  Unit 6103
Cummins ISM 450
Allison 4000MH

Re: Is this normal for cruise control?

Reply #35 –
Also max braking RPM which is often 10% above that under power.
Regards,
Brett

'99 42' Foretravel Xtreme
'14 Brown Motorsports Stacker
'05 Chevy SSR
'02 BMW R1150R

Re: Is this normal for cruise control?

Reply #36 –
I agree that this is very informative article and I have learned a lot too. I have always just left it in the Economy Mode and downshifted manually in the mountains but it can certainly help improve the way I do it. Thanks Brett!!!
John Smith
1994 U280 36' John, Pauline, & Marley Cat
2010 Ford Fusion

Re: Is this normal for cruise control?

Reply #37 –
Quote from: wolfe10 –
Yup, there are some critical numbers every DP owner needs to know for their engine-- call you engine manufacturer with your engine serial number:
Now that my head is immersed in stuff I had no idea I might need, one more question: What is a "DP owner" ?  :help:
1993 U-240 "La Villa Grande"..CAT 3116 w/ Pacbrake PRXB...Allison 3060 6-speed..
Previous: 1983 Airstream 310 turbo diesel, 1979 Airstream 280 turbo diesel
                                      Build # 4297
                                      PNW natives
                      Home base:  'Cactus Hug' (Ajo, Arizona)
                        DW Judy & Chet the wonder dog
                        Full-Timers 'Sailing the asphalt sea'

Re: Is this normal for cruise control?

Reply #38 –
DP= Diesel Pusher
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Is this normal for cruise control?

Reply #39 –
You knew that Mike ;D  ;D
Larry Warren
1996  U320 36' SBID "Lola" sold 2020
Build #4970
Motorcade #18318
 

Re: Is this normal for cruise control?

Reply #40 –
Quote from: ohsonew –
You knew that Mike ;D  ;D
There are SO MANY abbreviations: the obvious stumped me!  :facepalm:
1993 U-240 "La Villa Grande"..CAT 3116 w/ Pacbrake PRXB...Allison 3060 6-speed..
Previous: 1983 Airstream 310 turbo diesel, 1979 Airstream 280 turbo diesel
                                      Build # 4297
                                      PNW natives
                      Home base:  'Cactus Hug' (Ajo, Arizona)
                        DW Judy & Chet the wonder dog
                        Full-Timers 'Sailing the asphalt sea'