A couple weeks ago I submitted a post regarding my '07 Tahoe that was exhibiting a loud metallic "snap" or "clunk" noise upon deceleration. After 7 weeks of battling this issue and three dealership visits without resolution, I have islolated the origin of the noise.
Through some experimentation, I discovered that the "snap" occurs every time the engine switches from V8 to V4 mode. As everyone on this form knows, the engine is programmed to switch into V4 mode frequently - from parking lot speed to freeway speed. Any time the engine senses a decreased load, it will go into V4 mode, and that's when I'd experience the issue.
Once I made this discovery, I brought the truck back to my dealer, and they were able to connect the scanner unit and command the engine - 1 cylinder at a time - to switch into V4 mode. This way, they can evaluate the operation of each of the "V4 mode" cylinders.
After doing this, the answer was clear - cylinder #1 has a bad lifter. Every time the command was made to cylinder #1 to enter V4 mode, there was the "snap" noise I've been hearing for 7 weeks.
So, problem solved. That's the good news. The bad news is that the repair options become very expensive. To replace the AFM-specific parts on the affected side would run $2K w/labor. To replace AFM-specific parts on both sides runs $3.5K w/labor. New motor $6.5K w/labor (all rates through GM dealer shop).
This truck had 225,000 trouble-free miles leading up to this issue, but now I'm facing some tough decisions. Still working through the options.
Bottom-line? If your Tahoe is exhibiting symptoms like mine was/is, check to see if it only happens when the engine switches from V8 to V4 mode. If it does, it's likely a bad lifter and your dealer can easily confirm it with a scanner test.
Good luck everyone!
Through some experimentation, I discovered that the "snap" occurs every time the engine switches from V8 to V4 mode. As everyone on this form knows, the engine is programmed to switch into V4 mode frequently - from parking lot speed to freeway speed. Any time the engine senses a decreased load, it will go into V4 mode, and that's when I'd experience the issue.
Once I made this discovery, I brought the truck back to my dealer, and they were able to connect the scanner unit and command the engine - 1 cylinder at a time - to switch into V4 mode. This way, they can evaluate the operation of each of the "V4 mode" cylinders.
After doing this, the answer was clear - cylinder #1 has a bad lifter. Every time the command was made to cylinder #1 to enter V4 mode, there was the "snap" noise I've been hearing for 7 weeks.
So, problem solved. That's the good news. The bad news is that the repair options become very expensive. To replace the AFM-specific parts on the affected side would run $2K w/labor. To replace AFM-specific parts on both sides runs $3.5K w/labor. New motor $6.5K w/labor (all rates through GM dealer shop).
This truck had 225,000 trouble-free miles leading up to this issue, but now I'm facing some tough decisions. Still working through the options.
Bottom-line? If your Tahoe is exhibiting symptoms like mine was/is, check to see if it only happens when the engine switches from V8 to V4 mode. If it does, it's likely a bad lifter and your dealer can easily confirm it with a scanner test.
Good luck everyone!
