Shifting issue...

[Denali2k8]

So have a couple issues, not sure if they are related. Haven't troubleshooted YET, but when I get home I will check trans fluid level etc. 2008 GMC Yukon Denali 6.2L w/ 6 speed.

When I back out of the driveway or a parking spot, when I go from R to D, it takes a few long seconds and when it finally goes into D it goes in noticeably hard. I have to hold the brake pretty hard to keep the truck from rocking forward. If I go straight from Park to Drive the delay and pronounced jerk is not there.

The other issues are hit and miss. The first one is that sometimes the truck shifts hard between 1-2, but I can't figure out what causes it.

The other issue I'm not sure if it's trans related, but cruising about 45-50 the truck will surge 500 rpm up and down. Not changing throttle input on my end, the truck just seems to think I'm giving it gas then letting off etc.

Thoughts on any / all of those?

 

[Hydrazi]

I have a similar hard shift between 1st and 2nd. So I am interested if anyone has an idea!

 

[2011SSVHOE]

Ummmmm, maybe a tps issue Idk. maybe disconnect the battery for a minute Idk!! it's worth a try and it's free.

 

[Denali2k8]

Ummmmm, maybe a tps issue Idk. maybe disconnect the battery for a minute Idk!! it's worth a try and it's free.

Battery has even since been replaced. Issue still remains. Between 40-50 mph, with constant pedal pressure, the rpms will spike 100-200 higher and then lower as the vehicle surges until I reach about 50mph.

Again, if I accelerate harder, the issue seems to be non-existent, but that could be due to going past the issue faster. Cleaned MAF and throttle body. Not sure where else to go.

The charging voltage does flucuate under 14 volts and the stupid place that changed the battery broke the bolt so the cable is just on the battery with out being tight. Could voltage drop affect performance?

Also, when vehicle is cold, it seems to not have the issue as bad with the surging....not sure. So lost....about to take it somewhere and have it diagnosed. Not happy

 

[2011SSVHOE]

The charging voltage does flucuate under 14 volts and the stupid place that changed the battery broke the bolt so the cable is just on the battery with out being tight. Could voltage drop affect performance?

Get that fixed for sure, eliminate the knowns. then go for the unknowns.

 

[Denali2k8]

Get that fixed for sure, eliminate the knowns. then go for the unknowns.

Battery post seems to have helped? Hard to tell without getting some heat in the motor and my morning commute is only 10 mins.

My voltage goes anywhere from 14.5 (guess) to a hair under 14 on the gauge. Is this normal? My old Silverado stayed true at 14.5 99.9% of the time....

 

[kbuskill]

These trucks have a sensor ring that wraps around the negative battery cable and senses how much draw is on the battery and then sends the signal to the BCM which in turn tells the alternator when to charge and when to turn off. It is supposedly to help save fuel by not having as much drag on the engine.

The fluctuating voltage is 100% normal for these trucks.

 

[Denali2k8]

Well new battery bolt and cleaned connection did nothing for the stumbling / flucuation.

I had a cam sensor code pop a month ago but hasn't since. Could a bad cam position sensor have an effect?

 

[Denali2k8]

This normal?!?

 

[Denali2k8]

Might be kinda hard to see, but the cruise is set and the truck rpm goes up and down, doesn't feel like its shifting just like im hitting the gas slightly and the letting off