Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
2011 Silverado with bucking underload, Tranmission?
I am hoping to get some help diagnosing a problem with my 2011 Silverado. Here are the specs:
-2011 Silverado 5.3 4x4 with 190,000 miles and has th 6L80e transmission, NO TROUBLE CODES
My issue is that at light throttle usually around 45% @ 90% load, and 100% Evap Purge I am getting a bucking sensation, almost like a misfire or Vacuum leak. I have access to a basic scan tool and have been trying to correlate the drive condition to data, and nothing has really stood out to me. Other than the above mentioned, I may need to get into the trim data but I need research how to interpret it. Is there a particular parameter someone can advise I look at? The problem use to be only at around 30-40mph, but now appears to has extended to higher speeds as well.
I've had one transmission shop look at it, and of course he recommends a $3600 dollar rebuild! Go figure! I would like to verify transmission issue if possible and/or rule out other potential issues. If I drop that kind of money on a rebuild, I sure as hell don't want to find the problem lurking around afterwards.
Since it is around maintenance, time I have replaced the following:
-Spark Plugs
-Wires
-Coils
-MAF
-Cleaned TB
-Checked for Vacuum leaks wit starting fluid around intake area
-Bypassed Vent hose and vent solenoid
-Added Shudder Fix to Transmission Fluid
-Transmission fluid has a little discoloration but not smelly or black
-Stoplight brake switch replaced
I'd appreciate any insight you all might provide! thanks!
Sounds like a misfire problem and not a transmission problem . Do you have access to misfire pids? Would help to isolate which cylinder this is coming from.
I suppose you could still be experiencing a torque converter clutch shudder, despite the addition of an additive. A quick test I've adopted is to get it to start bucking, then very lightly tap the brake pedal. Not enough to apply the brakes, just enough to trip the switch. If the symptom immediately goes away, it's because the TCC quit applying. If it makes no difference, proceed with further diagnostics.
Or, you can try applying the Tow/Haul switch before taking off, and see if the issue disappears. I'm not positive about the 6L80E, but earlier GM trucks wouldn't apply the TCC with Tow/Haul activated.
