- Jul 22, 2015
- 2,724
Hoping I can get some confirmation / clarification on what might be happening here...
Background...
2003 Envoy, w/ 5.3L, about 145K on the clock...
Professionally rebuilt by local mech about 1yr (< 1000mi) ago - HD clutches / band, Beast, 3200 stall, PWM disabled, Vette servo, etc. Set up for towing. Derale stacked plate cooler. Temps consistently 150-170 F, per Torque.
Fluid looks fresh out of the bottle (light pink); level good.
Not one issue until recently.
A couple of weeks ago, when I was in the middle of a drive (fully warm / hot), I started hearing a whine...best I can describe it is as if I were driving a larger truck (like a TopKick or a semi). The noise would persist in all 4 gears and into OD (although lower in volume / pitch, as shifts progressed, was constant).
Did some research and originally suspected idler pulley. Figured out a couple of days ago that it's definitely the trans.
1-2 is very firm (not harsh, not 'slamming'), and a shade late. Other shifts are firmer, but less noticable. The truck also feels like it's 'struggling' a bit under acceleration from a stop - as if it had some type of internal resistance.
I figure that the line pressure has been maxed out. Shift points in 2-3-4, OD seem to be the same.
The other thing I noticed is that there is NO data via Torque - all other data points are fine / look normal - but no data on the trans temp. I know it's not running 'hot', and I know the pump is still working (not seized) - otherwise, it would have locked up by now, is my thinking.
So I figure that the PCM has lost communication w/ the trans, and consequently boosted the line pressure to compensate.
Being an '03, there's no separate TCM.
There are also no codes pending / stored, no CEL.
Now here's something very strange - a couple of periods during the 3 trips I've made with the truck (2 of them the other day, when I drove it to / from work, due to flooding (rain)) - I noticed that the whining stopped, and the trans behaved absolutely perfectly again. However, there was STILL no temp data in Torque when these instances occurred.
I can drive the truck at highway speed (55-70mph); the one time I did, was one of those 'good' periods that I described above - 20mi, no issues for the rest of the drive until I parked the truck at work.
The truck is supposed to go in in Sept. for 1yr checkup (to extend warranty another year).
If this is still ongoing then, I'll take the shop for a drive and demo it for them.
However, I'm going to be under the truck doing some other stuff, and if I can fix it before Sept, I'd like to do so. By 'fix', I do not mean dropping the pan or removing the trans - if that needs to be done, it's going back to the mechanic.
During my search on this, I've seen some possible reference to a bad TCS - not sure if that's relevant or not. Right now, I can't find info applicable to my issue online - and I don't have my ATSG manual handy at the moment.
If any of our knowledgeable transmission / 4L60 people might have an idea, I'd appreciate any info. Thanks in advance.
Background...
2003 Envoy, w/ 5.3L, about 145K on the clock...
Professionally rebuilt by local mech about 1yr (< 1000mi) ago - HD clutches / band, Beast, 3200 stall, PWM disabled, Vette servo, etc. Set up for towing. Derale stacked plate cooler. Temps consistently 150-170 F, per Torque.
Fluid looks fresh out of the bottle (light pink); level good.
Not one issue until recently.
A couple of weeks ago, when I was in the middle of a drive (fully warm / hot), I started hearing a whine...best I can describe it is as if I were driving a larger truck (like a TopKick or a semi). The noise would persist in all 4 gears and into OD (although lower in volume / pitch, as shifts progressed, was constant).
Did some research and originally suspected idler pulley. Figured out a couple of days ago that it's definitely the trans.
1-2 is very firm (not harsh, not 'slamming'), and a shade late. Other shifts are firmer, but less noticable. The truck also feels like it's 'struggling' a bit under acceleration from a stop - as if it had some type of internal resistance.
I figure that the line pressure has been maxed out. Shift points in 2-3-4, OD seem to be the same.
The other thing I noticed is that there is NO data via Torque - all other data points are fine / look normal - but no data on the trans temp. I know it's not running 'hot', and I know the pump is still working (not seized) - otherwise, it would have locked up by now, is my thinking.
So I figure that the PCM has lost communication w/ the trans, and consequently boosted the line pressure to compensate.
Being an '03, there's no separate TCM.
There are also no codes pending / stored, no CEL.
Now here's something very strange - a couple of periods during the 3 trips I've made with the truck (2 of them the other day, when I drove it to / from work, due to flooding (rain)) - I noticed that the whining stopped, and the trans behaved absolutely perfectly again. However, there was STILL no temp data in Torque when these instances occurred.
I can drive the truck at highway speed (55-70mph); the one time I did, was one of those 'good' periods that I described above - 20mi, no issues for the rest of the drive until I parked the truck at work.
The truck is supposed to go in in Sept. for 1yr checkup (to extend warranty another year).
If this is still ongoing then, I'll take the shop for a drive and demo it for them.
However, I'm going to be under the truck doing some other stuff, and if I can fix it before Sept, I'd like to do so. By 'fix', I do not mean dropping the pan or removing the trans - if that needs to be done, it's going back to the mechanic.
During my search on this, I've seen some possible reference to a bad TCS - not sure if that's relevant or not. Right now, I can't find info applicable to my issue online - and I don't have my ATSG manual handy at the moment.
If any of our knowledgeable transmission / 4L60 people might have an idea, I'd appreciate any info. Thanks in advance.