CountryBoy19
Full Access Member
I've owned my Yukon XL for about a month now.
Details: 2005 XL, 5.3L flex engine with GT5/G80 rear end, 116k miles
Known: The rear end has some backlash in it; you can sometime hear a "clunk" when transitioning from brakes to accelerator. I'm certain it's in the carrier/spider-gears/locker and I've faced the reality that I will likely have to replace it eventually. TPS readings (the best I can read them on my Torque Lite app) fluctuate about 3% in a cyclic manner while the surging is happening.
Symptoms: With cruise control on, at very low throttle-positions, descending hills there is a continuous cyclic surging of power, like somebody is repeatedly tapping the accelerator pedal. It's noticeable enough that my wife, that knows nothing of cars asked what was wrong with the car.
Has been doing this since we bought it but only on hill that have the right downhill grade.
My thoughts: At that low throttle position something is causing the cruise-control algorithm to get into an unstable controlling situation in which it "over-corrects". IE, it backs off the throttle too much slowing the vehicle too much, so it gets back into the throttle but once again, too much, and accelerates too quickly. It's possible the backlash in the rear-end is contributing to, or all-out causing this problem. But I really don't want to go through a rear-end rebuild already. Additional thought, the speed sensor used to control the vehicle speed is on the output shaft of the transfer case (or transmission?) right? So the ~1/8 turn free-play in the driveshaft could be causing a fluctuating vehicle speed reading right as the vehicle switches from being driven by the engine, to the inertia of the vehicle driving the engine. This would make sense...
Has anybody else experienced this?
Details: 2005 XL, 5.3L flex engine with GT5/G80 rear end, 116k miles
Known: The rear end has some backlash in it; you can sometime hear a "clunk" when transitioning from brakes to accelerator. I'm certain it's in the carrier/spider-gears/locker and I've faced the reality that I will likely have to replace it eventually. TPS readings (the best I can read them on my Torque Lite app) fluctuate about 3% in a cyclic manner while the surging is happening.
Symptoms: With cruise control on, at very low throttle-positions, descending hills there is a continuous cyclic surging of power, like somebody is repeatedly tapping the accelerator pedal. It's noticeable enough that my wife, that knows nothing of cars asked what was wrong with the car.
Has been doing this since we bought it but only on hill that have the right downhill grade.
My thoughts: At that low throttle position something is causing the cruise-control algorithm to get into an unstable controlling situation in which it "over-corrects". IE, it backs off the throttle too much slowing the vehicle too much, so it gets back into the throttle but once again, too much, and accelerates too quickly. It's possible the backlash in the rear-end is contributing to, or all-out causing this problem. But I really don't want to go through a rear-end rebuild already. Additional thought, the speed sensor used to control the vehicle speed is on the output shaft of the transfer case (or transmission?) right? So the ~1/8 turn free-play in the driveshaft could be causing a fluctuating vehicle speed reading right as the vehicle switches from being driven by the engine, to the inertia of the vehicle driving the engine. This would make sense...
Has anybody else experienced this?
