X15 Cruise control droop and engine brake response.

[marek4792]

So on insite there's a feature that can engage the engine brake when switched on with cruise control engaged to usually 2mph (low)/3mph(max) over selected speed usually used in rolling hills and not in steep mountain grades. The issue I'm having is the truck seems to wait until about I'm 4mph over selected cruise speed before engaging the low stage. My truck is programmed with a 2mph lower and upper droop and I'm wondering if I zero out the cruise control droop if the engine brake will respond at exactly 2mph over instead of the 4mph it is now, math seems to say yes but nowadays I never know.

[marek4792]

That's my thinking but what I don't understand is that on the older trucks even the 2350 I drove for a short time that with the low stage jake set to engage at 2mph over it would engage at 2 over with the droop at factory settings.

[marek4792]

It would explain why the few snapshots I saw on here while researching this had the upper droop set to 0mph

[Chamberpains]

To the OP, is your speedo right? Are the tire rotations in the ECM correct to what size tire you have.

**edit** I see now that you have the lower droop set to 2 mph. Yes, zero out the lower drop. Its giving you an extra 2 mph above the set speed. I also max out the upper droop to 3 mph. It keeps the cruise from being so aggressive when confronted with a slight uphill out on the flats with CC on.

I believe that LRT1549 has which droop is which backwards. If you can correct this, it'll keep the quick answer readers from getting it backwards as well.

I pulled this for any one wondering what droop is. (It used to be simply googled and found on cummins site but not any more)

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Cruise Control Lower Droop:

During normal operation, as a vehicle negotiates a down-hill grade, the fueling required by the engine to maintain the set vehicle speed will progressively decrease. By slowing the reduction in fueling and allowing the vehicle speed to exceed the cruise control set speed limit by a small amount, the positive effects of momentum can be utilized in anticipation of the next up-hill grade. Cruise Control Lower Droop refers to the increase in speed above the set vehicle speed that the vehicle may travel in down-hill circumstances. The available Cruise Control Lower Droop range is between 0 - 3 MPH. Setting Cruise Control Lower Droop to 3 MPH will allow the vehicle to exceed the set vehicle speed by 3 MPH before limiting fueling and provide the maximum benefit that may be gained from vehicle momentum. Setting Cruise Control Lower Droop to 0 MPH will minimize the effects of momentum but will provide the best speed control during these circumstances.


Cruise Control Upper Droop:

During normal operation, as the vehicle climbs an uphill grade, the Electronic Control Module will provide progressively increasing fueling to the engine in order to maintain the set vehicle speed. Continued up-hill climbing could eventually result in the maximum fueling rate being attained with little to no positive impact on vehicle speed. Cruise Control Upper Droop can minimize fuel consumed in these circumstances by automatically reducing the set vehicle speed by between 0 - 3 MPH. The time the engine spends at maximum fueling is thus reduced and fuel economy positively influenced. Setting the Upper Droop to 3 MPH will provide the best fuel economy benefit, while setting it to 0 MPH will provide maximum performance in these circumstances with no positive effect on fuel economy.

[marek4792]

Zero'ed the lower droop engine brake responds at 2mph over set cruise speed! Much better!

[Lonestar10]

I turned the cruise/Jake interaction on as soon as I got insite so nice not having to kick the cruise off on every hill to engage the Jake.