Can the cruise be modified in its operational characteristics?

[GM Guy]

Hey all,

I had an idea and wanted to bounce it off you guys.

How hard would it be to change how the cruise operates on a DS4 truck? Would it matter if it was OBD-I or OBD-II?

Basically what I am looking for is something that mimics Caterpillar's "Soft Cruise" which essentially lets it fluctuate by 3-5 mpg before pulling back the fuel or giving it fuel. Basically in low rolling hills it would drastically help mpg.

Another alternative that may be more simple is a constant fuel rate cruise setting, and let it fluctuate that way.

Any thoughts?

 

[schiker]

I imagine the cruise aggressiveness could be changed by someone that can program.

Maybe the constant fuelrate mode could be done with a switch and parallel circuit to the fuel pedal input? I don't know I think the fuel pedal is possibly a potentiometer like device? Might could take one apart and figure a way to take the spring out and fix the foot lever to a set point. Might could rig up a switching device to use one or other. A mechanical IP could be rigged like a tractor have a second cable run to lever that holds a position couldn't it. Either model I imagine speed would fluctuate a good bit unless it was really flat and straight.

Not sure how much MPG you would gain. I think speed drag is very important then acceleration is 2nd factor in MPG. The rolling hill speed gain might be ok but I imagine depends on varying total weight. It would be nice to adjustable for towing mode.

Both conservative modes would be a rural area mode and or flat area. On any busy interstate it would probably cause a lot of traffic knots.

 

[THEFERMANATOR]

GM did this with the DURAMAX, and I HATE IT! At least the 02 operating system is this way. It will drop down about 3-5 MPH before it really starts to bring the throttle in, and by that time it hasn't really come up on boost, and has to go full bore and downshift to maintain speed on steep overpasses by the time it finally fuels. I normally put my foot into it when I know I'm approaching an overpass just so it won't have to downshift to keep from losing speed. I wished I could set my cruise more aggressive, but I don't have that available in EFILIVE.

 

[schiker]

Yeah, I was thinking this is a personal preference setting. And it will depend on traffic, load and terrain. Some adjustment would be nice. Maybe a lock in OD would work in a non tow/haul setting. In heavy traffic sometimes 3 mph drop feels huge though. Sometimes I dislike being passed for one car length and or the squeeze in to my safe trailing distance. Seems it is just getting worse and worse with more and more inconsiderate drivers.

With a manual transmission it doesn't have the ability to downshift and go to extreme catch up mode so I don't get that but have felt it in other vehicles. I have not used much cruise lately (isn't working) but it applies more fuel and seems softer with a manual. I have to watch for serious disengagement harshness though.

 

[Will L.]

I did a bit of testing with a Chrysler LHS I owned years back. The tighter I kept the limits on it the better mpg it got. The most extreme was at 15 mph variation I would loose 2 mpg vs keeping it at 1 mph variation. Gas engine and way different aerodynamics, etc.
Maybe truck would be different.

Being able to play with it is worth the time if you can figure out how. Sorry no ideas, Good luck.

 

[GM Guy]

I forgot to mention, this will be on a manual trans. vehicle, so we don't have to worry about controlling shift points, etc.

 

[schiker]

Will that actually doesn't surprise me thinking its minimizing the amount of acceleration back to up cruise speed.

But I imagine it really depends on terrain and how steep the hills get and or how fast it gets steep. Such that how much the speed drops. With more modern transmissions that coast better is where the change to flexing speed more has come from I imagine. My wife's BMW actually compression brakes to not overspeed while on cruise. Getting a speeding ticket with the cruise on would suck so I can't say its a bad thing.

 

[NVW]

I forgot to mention, this will be on a manual trans. vehicle, so we don't have to worry about controlling shift points, etc.

With you what could it be but a Manual Shifter?

 

[schiker]

For the DS IP's

Just thinking I don't know I wonder if with a manual transmission you could engage a high idle circuit and get a fuel rate cruise control that might hold a somewhat steady MPH and produce a good MPG for rural flat land driving.

Depending on rear end gear and 4th or 5th gear 1600 rpm high idle and flat land it might hold 50-60 mph and kind of fluctuate with head wind ???? Would probably over speed downhill depending on speed and gearing???

Quick thought I haven't really thought about it but might could do a push button and latch type relay through the brake pedal and or clutch ???? I think the clutch kills the high idle but not sure if brake does but its only momentary break isn't it.

 

[GM Guy]

and then the final thought to ponder:

Detroit Diesel had a split horsepower rating of 430 HP on the Foot Feed and 470 on cruise on the Series 60 truck engine in the mid 90s. I think the thoughts were to try and get the drivers to use the cruise, probably used more fuel in the hills, but on the flat probably prevented fluctuating speeds and "pulse foot" driving and thus boosted fuel economy.

Could a guy somehow incorporate something like that on a 6.5L?

As far as the high idle, that sounds like a great idea, as a guy should still have the safety of everything kicking out when the brakes are clubbed. One would have to see if the ECM would mind if the speedo was moving while on high idle. Unfortunately, that would only really come in handy on a 3.73 or 3.42 geared truck while empty with that kind of RPM.

 

[SmithvilleD]

Believe my '95 high idle operates with speedo showing movement. Haven't tried it above about walking speed, but it happily did that. Picked up a few stray small bales with truck loafing along in the field.

 

[tanman_2006]

I want the same thing. My biggest issue is the sudden flogging it gives the truck to regain speed. I'm with everyone else that a tight cruise would net best mpg or a fuel rate setting that allowed some foot help on hills.

 

[JayTheCPA]

Am thinking that the best way to hold speed is set the ECM to keep the TCC locked on decel and rapid decel. Naturally this does not apply for the manual tranny. Aside from the two 'check-box' settings, am not aware of a cruise control set of tables in the ECM's code. Aside from 0 throttle, downshifting, and / or braking for controlling the downhill speed while in cruise, the only other thing out there is a driveline retarder, but those things are expensive.

To really make a solid cruise that maximizes mileage, the system needs to read inclination and map that into the speed control. I know that Mercedes did this in the 80's by sensing the inclination and getting the system to engine brake on downhills which then kept the uphill acceleration much smoother as there was no need to drop speed prior to bringing in the accelerator during rolling hill scenarios.

IIRC, GM did a somewhat configurable cruise control with an 'Econ' and 'Normal' settings in the early - mid 80's. Do not know how the two settings were actually controlled, but the 'Econ' setting allowed the speed to fluctuate and the 'Normal' setting kept the speed fairly tight. I set the cruise in 'Normal' as the 'Econ' setting was annoying.

To really make a good cruise system that can maximize mileage, it needs inclination and look-ahead capabilities so that the system can measure the current incline and then look ahead to see what is coming down the road. IIRC, British fighter jets from the 2000's had this type of technology with terrain following systems that let the pilot go supersonic and set an 'above the ground' altitude; talk about putting your life in the hands of a set of electronics.