Hi,
My 2001 XK8 takes a very long time to accelerate (even longer when starting cold). I also feel heavy vibration occasionally when speeding up. And once I reach 70mph, it doesn't go beyond that. I am getting different diagnoses from mechanics (timing belt, cat converters and one said engine misfire). Instead of finding true cause by trial and error (and keep spending money), I wanted to get your opinion about what the issue most likely could be.

 

Do you have a MIL light on (check engine)? With a scan tool, what fault codes come up? Any warning messages in the instrument display?

Does the car stumble when accelerating or not at all?

 

I got Engine misfire codes but the car ran fine for several months. It just recently started with sluggish acceleration. It's hard to find any reliable mechanics for Jaguars around my area unless I am ready to pay in thousands for any repair. I had replaced the spark plugs and can replace the ignition coils (for whichever cylinders are misfiring) too if that would help.

 

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Without much actionable information it is difficulty to be confident in any assessment. Nevertheless, I’ll fall
back on the old, “..if it were my car” line.

With that in mind, it sounds like to me your engine is simply not getting enough fuel due to a partially blocked fuel filter.

At low demand, fuel sufficient fuel may pass thru. Hence the problem only, or mainly, being evident during the high fuel demand scenarios of acceleration and 70 + mph operation.

even if you can observe fuel being released when the schrader valve is depressed, I would highly recommend replacing the fuel filter. The cost is minimal and, without knowing the service history, probably is overdue for a new fuel filter anyway. Note: even a fairly new filter can partially clog if there is debris in the fuel tank.

The replacement will only set you back $15 more or less, and takes only 15 minutes to accomplish.


Motorcraft Fuel Filter (from Amazon)

https://a.co/d/dH7ufuC

Z

 

And if you fill in your location ..top right it would help us to help you.

 

It should be obvious if the engine is misfiring. You could unplug the coil packs one by one with the engine running. If you unplug a coil pack and the engine note changes then that cylinder was probably firing correctly. If the engine note doesn't change then that cylinder was misfiring. You could then try swapping plugs and coil packs from a good cylinder to a bad cylinder. If the misfire moves with the plug/coil move, then the plug or coil is faulty. If the misfire doesn't move, then it suggests an injector or compression issue on the misfiring cylinder and you can investigate further.

Fault finding this way does take some time but it doesn't cost anything.

Richard

 

A code reader will tell you which plug it is without all that swopping ****

 

Once the code reader, which the OP clearly does not possess, has identified which cylinders are misfiring, you then need to do the swapping anyway to identify the reason for the misfire. Identifying which cylinders, if any, are misfiring (as the OP doesn't seem to be sure about whether there is actually a misfire), simply requires unplugging the coil packs which is a simple job and requires no swapping and no special tools (such as a spark tester etc).

Maybe my 55 years of spannering has resulted in all jobs looking easy? 😉

Richard

 

My 60+ years of automotive experience has the opposite effect.

The more experience I have, the more I realize how much I have to learn.

 

Watch most modern-day mechanic deal with a set of carburettors or a set of points. I've spent a lot of time over recent years sorting out the total shambles they leave behind. These days they simply swap out the old parts for new ones until the problem goes away. I'm not sure whether that actually requires any skills at all?

Richard

 

Agreed. Thank goodness for this forum.

 

I had similar issues and replaced the fuel filter and that cleared it up. You can test the fuel pressure at the fuel rails to see what it is. I think its supposed to be about 40 PSI.

 

Sorry that I'm a little late chiming in, but having a point of view similar to Z's, I would also add to check for air blockage such as a clogged air filter.
Ref: A notorious 85 T Bird a had.

 

Note: checking for fuel pressure at the fuel rail’s schrader valve is not always a conclusive indicator of a free flowing fuel filter. At low demand enough fuel can flow thru a partially blocked filter to allow pressure to build up and appear to be sufficient.

its only during the high fuel demand scenarios, such as the OP has described, that the partially blocked filter will be evident.

Z

 

50 - 55 psi

 

@giandanielxk8
@zray
@Pistnbroke
@RichardS
@David Dougherty
@Dr. D
@michaelh
Thanks to all of you who took time to read my post and respond with your valuable advice/suggestions. I will certainly follow your leads and will share the results here. Thank you.

 

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Don’t take too long. I can’t hold my breath forever.

Plus I feel badly for you that you can’t go over 70 mph in a Jag, any Jag.