X308 2K Misfiring on both banks

After having “tried everything”, I am seeking wisdom on this issue I’m having with my 2000MY XJ8 3.2 litre.

The car does not perform properly. It will start and idle but will not perform properly when driven. It seems to be missing continuously on one particular cylinder on each bank (even on idle); I can tell by the even exhaust stream being methodically interrupted thus not running as softly as it should.

Since I picked the car up last spring, when it was barely running at first but picking up as the journey progressed and with the addition of more fuel and jeg cleaner, I have replaced the spark plugs and all the coils to no avail.

The engine was replaced under warranty (not nikasil at this late MY) at 60K miles, and it currently stands at less than 120K miles.

Any insight would be greatly appreciated!

Kind regards,
Bard Thomas

If it’s not spark, it must be compression or fuel.

Dead injectors will cause misfire.

Hi Bård,

Have you performed a compression test on all cylinders to eliminate a leaking, sticking, bent or other type of valve issue?

Often, a rhythmic misfire heard at the exhaust, is a sign of a burnt exhaust valve or otherwise leaking or sticking valve(s).

Kind regards,


Fortsatt, god jul og godt nyttår.

Thank you! Then engine being quite new, I didn’t expect it to have any valve related issues but I could easily perform a compression test.

I forgot to mention; I had the dealer run a diagnostic on the engine. They did get an error code relating to one of the catalyst CO sensors but that was all…

Compression test next!

Takk for det, Chris!

Just performed a compression test. Here are the numbers (psi):

Bank A (right side) - 1: 200, 2: 208, 3: 205, 4: 225

Bank B (left side) - 1: 200, 2: 200, 3: 200, 4: 190

Checked all the plugs and they were in quite a similar condition, which tells me the jets should be ok as well. I thought I’d get a laser thermometer to read each cylinder’s temperature to verify this…

Any thoughts?


I think your on the wrong road
Change the fuel pump and filter
Have you ever changed the pump?
On another thread these pumps don’t last long
How much gas is in the car?
They implode internally causing blockage and restrict flow
60,000 on the new engine like I’ve said before is average for a 308
They were meant to go 100,000 and basically that’s it
You could have a ecu issue but
I’m betting on the pump!
Get em tiger!

Bona sera, Limongelli!

I never replaced the fuel pump but it is in the tank, I know, and so hard to get to that most hack a hole in the parcel shelf to get to it. I won’t though!
Filter? OK, I’ve got a filter laying around here somewhere, because that too is so hard to get to, so I chickened out the last time I was going to replace one… (not same car…).

The filter might be the place to start though…

Gracie mille!


I think we found the problem…
Find a shop a tow it there
Change the pump and filter
I think you will be surprised!
Do them both together don’t monkey around with the filter without the pump
Good luck!

Ok, I’ll get a pump too but, I do like to change one thing at the time. Since I do 98% of the repairs to all the cars in the family; some 6-7 Jaguars and Mercedeses, I do it like this to build up experience, and get to know what the culprit was.

Thanks a lot for the tips though!


The problem is the filter wil have junk
Then your pumping more junk
The pump is the issue
I think you will be hapoy
Good luck

Sorry I got cut off
Ok good luck take your time
That pump is a real crappy job
There’s a great video on you tube…
It could be worse when I do Aston Vanquish pumps you have to make sure you life insurance is up to date😀

Without comment about the likelihood of a worn pump causing these symptoms, and after just changing the pump on my wife’s XJ8 and knowing the pain involved, I say it makes no sense to change the pump unless the fuel pressure is low. These cars (unlike the x-300) have a fuel pressure test port on the rear of the right fuel rail. Rig a long enough hose to be able to watch the gauge while it is taped to the outside of the windshield. Carry a fire extinguisher if you feel nervous! The pressure should maintain about 40 to 46 psi gauge pressure depending on the current manifold pressure as you accelerate or any other condition.

You did not mention any OBD codes, so I assume there are none? Have you tried the “Italian tuneup”? Do you know what the fuel trims are doing? If not, why not? :slight_smile: