Hello All,

I just purchased a 2011 XKR175 with 94K on the clock a couple of weeks ago. I got a PPI and overall the car is very clean. I’ve run into this weird issue, however, where something, I think the engine, shudders at between 1500 and 1750 revs only in gears 4-6. The problem is consistent, but I can’t find any reason for it. The car idles smoothly and all fluid levels are staying consistent. Any help would be much appreciated, thanks for all the great info on these forums!

-mushroom09

 

It is vibration caused by the header design and exhaust flow under certain low RPM conditions with some throttle applied.

There are two solutions:

One, you can search for additional parts to hold the exhaust in a way it can't build the vibration. Not sure how expensive these might be these days.

Two, shift down one gear in places you know it would happen.

 

At that mileage you might check the motor mounts as a contributor too.

 

Hi Tervuren,

I was under the impression that this was a TSB for the 07-09 XKs but was solved from 2010 on, but I'll definitely take a look. Thanks for your help!

-mushroom09

 

Hi pwpacp,

Thanks for the suggestion! Motor mounts were one of the culprits I was going to look into, among coils, spark plugs, dirty injectors and possibly issues with the e-diff. I'm still perplexed as to why the issue only happens in certain gears at certain revs, but I'm guessing now that it has something to do with a resonant frequency at certain engine speeds and loads that causes a vibration from somewhere else in the vehicle.

-mushroom09

 

Start with the injectors.
Its an impossibility that they are not filthy at that mileage.
Those are the symptoms you would get.

You know how to clean them?

As to why it happens in certain gears and revs.
That's when load on your engine is the greatest.

 

Hi Queen & Country,

That makes sense, I’ll definitely look into it. I haven’t done it myself, are you referring to a cleaning such as running BG44K through it? There’s a shop that does BG services near me and I considered that as a first option but at the time I didn’t think that this kind of issue would cause problems at only certain rev ranges and gears. Thanks for the input!

-mushroom09

 

I mentioned it because its something that has to be done regardless and has the potential of solving the problem, so its process elimination.
Direct injection injectors are highly prone to fouling.

When we were kids, we would test the strength of an engine by seeing which one could climb uphill in top gear.

 

Ditto, need to isolate whether it's a loss of power or a resonant vibration. Should be able to look at rpms via an OBDii scanner that will be more exact versus the dash gauge.

 

Update:

I had a private shop pull the codes and look at details and they are thinking it’s likely the transmission. It was throwing weird voltages for pressure control solenoids 3 and 6. Looking into it right now. Thanks for all of the help so far. I really appreciate it!

-mushroom09

 

Turns out that the issue was actually bad motor and transmission mounts. Had them replaced by an indie shop that I like and all is running smoothly now. I appreciate all of the help from everyone, it’s great to have an active community for such a special car.

Cheers,

-mushroom09