2007 Suburban Shudder Under Load
Help! I need fresh eyes on a problem i'm having with my vehicle. I have a 2007 Suburban LTZ with 290,000 Miles. I've always run Mobil 1 but for the last 2 oil changes, I used Valvoline MaxLife. I personally rebuilt the transmission at 202,000 Miles due to a broken forward sprag and replaced the torque converter at the same time just in case. Recently, it started experiencing a shudder starting around 45 MPH when the torque converter clutch is engaged. Once the TC is locked, when you slowly press the gas pedal, the car will start to shudder. if I keep steadily pressing the pedal and it doesn't unlock, I can cause it to shudder all the way up to 70+ MPH. Also, while it's shuddering, the speedometer dial with bounce up and down about 1-3 MPH. It almost feels like lugging such as when you have a manual trans in 5th gear but are only going 20 MPH.
I noticed a pretty rough idle last September along with some misfire codes. Did the cylinder soak due to oil consumption while I had the plugs out. I replace the plugs and wires and the problem went away. That was 15,000 miles ago. Over the last couple months, the shudder started. It was really bad at first so I replace the ignition coils which made a significant improvement but the shudder was still there. I also noticed that it seems like the engine is losing all power at low speed occasionally for about 1/10th of a second. Things I did after September but before the shudder started:
Things I've done so far to troubleshoot:
Things I plan on doing next:
What are your thoughts on this?
I'm hoping this is a simple electrical issue that I'm missing. I don't want to decouple the trans from the engine yet again to replace the torque converter. I'm too tall to be crawling under there. I really need a lift! I also don't want to have to remove the heads and replace lifters. After installing new plugs yesterday, it started throwing an air bag code. The right front sensor is showing erratic data. I was nowhere near that sensor or wiring that I know of. Hope it's just a wire issue, otherwise, there goes another $70.to the auto parts supplier. Thanks in advance! |
05/30/2019 Update:
Switched back to the original ignition coils. Problem persists. Performed compression test. Did two dry tests. All looks good to me. Code:
Cyl Test #1 Test #2 Avg Code:
Gear 700 RPM 1500 RPM |
Today, I decided to do one more troubleshooting step to hopefully eliminate the engine or something else electrical as the cause. This involved modifying the TCC PWM Solenoid to essentially be an on / off switch instead of modulated. To do this, you remove the o-ring on the end and the screen so you don't damage it. You then grind a notch in the two raised areas on either side of where the o-ring was. Reinstall the screen but not the o-ring. Install in transmission.
Took it for a test drive and absolutely no shudder now. You can feel the torque converter engage and disengage now but it locks up fully. No shudder and no slipping while engaged. This eliminates the engine as the cause. The question now is, what's causing the torque converter to not fully lock up with the TCC PWM solenoid in stock form?
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