2000 xj8L has a shimmy or vibration under medium heavy acceleration no codes or lights,new plugs installed,engine runs strong but vibrates pretty good under heavy load. passed emissions today, no codes, a friend suggested checking u joints and front end suspension components. Is this a good place to start? Has anyone had this problem before?
Thanks in advance!!!

 

check brake rotors and pads, you most likely will need an alignment too, my car does the same around 60 - 80 mph anythng over is smooth but i know i need an alignment

 

Only vibrates from dead stop or when going into passing gear, or darting on a hill.

 

Swurvn,

Sounds like we have a similar issue. My 99 will shake only when I'm at freeway speed and go to pass someone. It's not a balance issue. There isn't a vibe anywhere from 1 MPH to 100 MPH when at steady state. It almost seems as if the torque convertor is locking/unlocking and the thing is confused about dropping down a gear.

Once I grab the shifter and manually shift it to 4th the car goes like a bat out of hell and the acceleration is as smooth as silk.

All other times (99.997%) the car performs, pulls hard and runs flawlessly to 7000 rpm. WOT shifts are strong and there is no indication of slip.

Because I have not experienced the issue other than on the freeway, I cant decide if it's a transmission issue or an ignition spark issue. I'm leaning toward spark because once in a great while (only 3 times this year) I get a misfire at idle when at a traffic light. However no DTC codes or CEL at this time and since the plugs have only 4K on them I'm not about to start guessing at the Coils which are $150 each.

I'll post here if I find the root cause of my issue.

Ken

 

could it be engine mount failure? They are fluid-based, and tear/leak quite common.

 

Swurvn,

I just finished an 800 mile trip and this issue is driving me crazy. Whatever the issue is, it's getting less intermittent. Basically it's getting worse and it's definitely a heat soak issue. The longer the car is run the worse it gets. I drove for 2.5 hours straight and it was sputtering every time I went to pass someone.

Still, no CEL or codes stored for me.

Since the temps will be above freezing this weekend I'm going to dive into this and see if I can figure it out.

Have you figured out what was causing your issue?

Ken

 

FWIW,

I'm beginning to think it's a dirty injector......

 

Hmmm...

 

$150/coil seems a bit high...