4.0 AJ16 loss of power over 2000rpm

[wizrod]

Hi all,

I have a '95 4.0 XJS Celebration, which has just started to show a loss of power above about 2000rpm.

It starts fine (from cold or hot) and runs smoothly up to 2000rpm, though the rpms dip quite low (<500) as I take my foot off the accelerator, when I pull up to a stop.

Above 2000rpm there is a gentle, and irregular hesitation; as if it were missing on random cylinders. This occurs whether accelerating or cruising. It doesn’t seem to be able to get above 22-2300rpm.

Note, the above were spotted with an engine that was up to temp, but not especially hot - 10mins urban driving.

Any thoughts on what the problem could be…? Given it is fine fine at lower engine speeds, I wonder if there is a fuel delivery problem? Is something stopping the engine from getting enough fuel to get past 2300rpm…?

Anyway - Tthanks in advance for your wisdom!

cheers

Paul

[davidr]

Hi - it does sound like a fuel starvation issue. First thought would be a blocked fuel filter. This is under the nearside (left) front wheel arch behind a plastic cover. It's worth changing that as a start. It's a service item and cheap and easy to replace.
Beyond that, the fuel pump may be defective but I would expect it to either work or not but I guess it's possible that it's not running properly.
Also have a look at the fuel pipes under the car as one may have been pinched or bashed so restricting the flow.
Hope that helps

[wizrod]

Hi,

Many thanks for your reply - very useful.

I've read somewhere, while researching this problem, that the fuel filter is nothing special (ie not jag/XJS specific) and that a 'generic' filter will be OK. I've even read that even a simple VW Beetle fuel filter will work. I only mention this as I have large stock of ACVW service parts for my small 'fleet' of classic VWs....which would potentially expedite addressing this. Is this valid advice?

I've also read that there is as second fuel filter at the fuel tank end (in a swirl pot?) that can get blocked too. Is this the case with all models/years? I understand that access to this is under the battery, so it should be a fairly easy check....?

cheers

Paul

[davidr]

Hi Paul - the filter you need has a thread at each end to fit the fuel pipes.
Here's a picture of the pipes, clamp and filter that is under the front left wheel arch.

And this is the filter itself

image.jpeg (11.87KiB)Viewed 2163 times

Prices are around £25 for a genuine Jaguar one and about half that for quality aftermarket brands such as Mann.

The second filter in a swirl pot does not apply to your car. This was the earlier models with external pumps. Your pump is in your tank. We published an article in the magazine a couple of months back about the swirl pots and filters and maybe that was what you read but, as I said, this doesn't apply to later cars like yours.
We also showed my fuel filter being changed in the March magazine with more detail in a thread on this link viewtopic.php?f=41&t=12439

[wizrod]

Thanks David,
That all seems fairly straight forward. If the weather holds, I should be able to get it all sorted tomorrow.
I'll report back on my progress
cheers
Paul

[greeban]

Worth replacing fuel filter anyway but if still a problem, assuming you only get this after warm up likely electrical , perhaps crankshaft sensor.

[wizrod]

So...Update time...

It would appear that replacing the 160000 mile old fuel filter has solved the problem

It turned out to be a remarkably easy job - I didn't even need to remove the wheel!!

Many thanks to all who made suggestions.

TYVM!

cheers

Paul

[davidr]

Excellent!! Pleased to hear you've solved the issue quickly, easily and cheaply.
Happy days