engine vibration

[seafeye]

@ seafeye

Look at your wheel rims for deformations.

Just got back from getting the wheels balanced.

Drives a bit better but still have the vibration.

The back left wheel is slightly egg shaped. Don't know how that happened, but it isn't completly round.

So back to ebay to find a replacement....

[david44tn]

I have a 2001 Boxster with the same symptoms as stated in the earlier posts. My vibration starts on acceleration around 3000-3200 in any gear and quickly goes away after the engine is out of this range. The vibration cannot be felt in the shifter or clutch pedal. It is very brief and can be felt through the seat, while accelerating during normal driving. When accelerating hard, the vibration is rarely felt (I suspect because the range passes by quickly). Deceleration is very different with the vibration much more pronounced in the exact same rpm range, and quickly goes away, starting around 3200 and gone under 3000 rpm, with any gear, although seems more pronounced in the lower gears. Some things to add. I have a new front motor mount. Also,the vibration cannot be felt with the vehicle stationary or rolling, with the transmission out of gear, clutch in or out with running the engine in the 3000-3200 rpm range. The vehicle has to be in an acceleration or deceleration (driving) situation in gear with the vibration to occur. I feel if I had a flywheel/clutch imbalance problem the vibration would be felt when the vehicle is stationary and reved to 3000-3200 rpm, it definitely doesn't happen then. I am now suspecting the rear/transmission motor mounts. I'm curious if anyone has replace theirs because of this vibration. Also to add, I haven't heard of anyone with a 996 with this problem, the dual mass flywheel/clutch is the same configuration, my thoughts are the difference of how the engine transmission assemblies are suspended comparing the Boxster and 996, maybe it doesn't occur in the 996. I would appreciate any thoughts to add to this. Thanks.

After doing lots of studying and measuring and experimenting on this subject, I finally came to a conclusion and a VERY SIMPLE remedy that I have tried on my 2001 Boxster that has worked very well to remove the vibrations as I described in my earlier post. My remedy may or may not work on your vehicle, according to the vibrations you may have. Let me say first, at 3000-3200 rpm these vibrations will be dominant over other engine speed vibrations if you have faulty mounts, including rear (transmission) mounts. First make sure your front engine (motor) mount is in good condition and with no rubber broken or missing. Also, to try this your Boxster will need to have the muffler support as mentioned in the earlier posts. (the one that attaches to the 8mm studs on the back side of the muffler and to the support on the rear of the transmission) My procedure is this: Park your Boxster on a solid level surface and find a good measuring reference point on your muffler (I used the forward edge of the outlet pipe) to use a locking measuring tape to measure the distance from the muffler to the floor, bring the locking measuring tape to the point and lock it to use for reference later. Next, loosen the fasteners (13mm nuts) on the ENDS of the muffler support on the muffler. Next, remove the jack from the luggage compartment, leave the jack crank intact, it is not needed, place the jack under the center of the muffler, in front of the outlet, I would suggest using a small piece of scrap plywood or lumber to place between the jack and muffer, turn BY HAND the jack up to the muffler until it is contacting the muffler and then raise the muffler NO MORE than 13mm or 1/2 inch, and with the jack supporting the muffler, tighten the support mount fasteners (the ones loosened earlier) on the muffler, suggested torque, 18ftlbs. Then lower and remove the jack and place the locked measuring tape at the reference point to see if the muffler has been raised by a few milimeters. I have found an adjustment of three/five milimeters makes a big difference in the vibrations. I have also found on my first experimental adjustment, the vibration was removed as I was driving going UP through to the 3000-3200 rpm range, but I still had a vibration on deceleration. After adjusting the muffler higher (app. 3mm) the deceleration vibrations were gone also. Hope this may help those that have had this problem. Thanks, David