Experiment for 2003-2005 LS8 owners

[shorod]

I've a request for owners of 2003-2005 LS8s. My car has a funny vibration that can most easily be reproduced with my car in park. If I very slowly increase the engine speed in Park, I can notice a vibration around 1500 rpms. If I hold the engine speed there, it will continue to vibrate. Sometimes it will feel like the car has a misfire while sitting at stoplights too. I had a V8 Taurus SHO before this and had to replace 3 of the coils in serial, and that felt just like what I experience with my LS8. On that one though, my scan tool picked up the misfires on the individual cylinders though and showed the exhaust for that bank going rich, so I knew it was a bad coil each time.

I originally thought this was a misfire. My scan tool registers knock counts when this occurs and I can hear a slight backfire in the exhaust, but my scan tool does not register misfires. I had my dad watch the engine while I got the vibration to occur and he could not see any vibration in the engine. He could hear the exhaust sputter though. When he sat in the car, he could definitely feel it and he mentioned he thinks it's a vibration rather than misfire. Possibly harmonic balancer or torque converter.

Since the car is under warranty, I've had it to the dealer 4 times now for this. The first two times I dropped it off and went to work. When I picked it up, they said they were not able to duplicate it. The third time their tech sat in the car while I increased the engine speed and said, "Yep, there is definitely something there." He got out the WDS scan tool and verified there are no cylinder misfires present. They tried the same on a new 2006 and it did not exhibit the vibration. They've been in contact with the Lincoln Hotline and tried the first set of suggestions, loosening and retorquing engine and transmission mounts, but I think that just made the vibration worse (and so does my wife).

Would other owners of 2003-2005 LS8s be so kind as to try this on their cars? Or if you've stuggled with a similar vibration and fixed it, I'd love to hear what it took as well. I'm sure the dealer would appreciate knowing the fix as well.

-Rod

[shorod]

Well, I'm still trying to track this vibration down. Recently I realized that the vibration in park and when sitting at a stop light feels very similar to a pulsation if I lightly lift off the brake pedal while at a stop.

If I let off the pedal just enough that the brakes are no longer locked, the car will attempt to pull forward with a pulsating feel, like the torque converter is just starting to engage. I can notice the same if I very gradually slow to a stop. Just before the car comes to a complete stop, the car will pulse.

This feels very similar to what warped brake rotors will do, but this is definitely not warped rotors. There is no hint of pulsation in the brakes under normal slowing, this only happens when the car is just barely moving.

Would anyone else with a 2003-2005 LS8 attempt this as well to let me know if this is normal?

-Rod