Hi there,

Been lurking and researching for some time on this forum and it's the best out there. Fixed quite a few issues from the advice given in threads here, so thought that I would throw this into the mix, to see if anyone could shed some light onto what may be wrong.

I currently own an early 2001 Jaguar XJR X308, which is completely standard, with the exception of an K&N air filter. It has been fully serviced all its life from the Jaguar main dealer and recently I have had quite a bit of work done. Gearbox oil change, Supercharger oil change, MAF sensor, new spark plugs, EGR pipe replaced, subframe 'V' mounts, steering rack, track rod ends and all new discs and pads.

The problem I have is each time I go to start her I get a very different car? This may sound a little strange but sometimes the engine seems flat, other times it is truly scorching with masses of torque. I never know which I will get. My first thoughts are the ECU mappings may be corrupt or not being loaded correctly? I have tried the hard resets many times, disconnecting the negative lead from the battery and touching the positive, but to no avail.

Other thoughts are that I may have a compression problem, as I noticed a little oil on the ceramics of one or two of the spark plugs when changing them out. But this doesn't seem to follow the logic when the car is running more powerfully.

So I am at a bit of a loss at the moment and would appreciate any advice.

 

I suggest you get a scanner that can trend chart LTFT, STFT, MAF value, and calculated load in order to compare engine operating parameters in one session vs. another. I doubt you have intermittent compression.
You might have something obscure like a fuel injector spray pattern, which is pretty much diagnosed by excluding everything else. And , does you throttle cable make a full actuation of the throttle plate mechanically? That has been known to limit the engine by 10 to 15 %.

 

Thanks Ross,

I have the ScanXL tool which I pair with the ODB II interface in the car. I have used a few maps around the MAF, but will try the others you suggested in conjunction. I looked quite extensively at the throttle area to try and diagnose this problem and found a couple of issues, mainly to do with strangulated or loose vacuum hoses, once fixed this improved thing quite a lot. But unfortunately not the irregularity.

The throttle plate seems to works correctly and fully opens and closes with the ignition on and a full press/depress of the pedal. I have cleaned all the electrical terminals on the throttle body and inside the body itself. Which was surprisingly clean.

In my ownership, I have regularly used injection cleaner in the fuel supply to try and rule out the injectors and recently had the fuel filter changed. What also seems a little strange is that the car appears to perform better with a full tank of fuel?

 

Sometimes the hose slips off the fuel pump. When the tank is full, the effect is less noticeable.

However, under fueling should have been picked up as a fault.

This might show up as high LTFT.

You would need to monitor fuel pressure at the rail to know for sure.

If you take out the tank, you may as well replace both pumps because it is an ordeal.

 

Yeah, I agree with Plums that you should check fuel pressure, although I do not believe yours could be the hose off anomoly. Maybe a plugged inlet sock. I have a long hose on my fuel test gauge and I tape the gauge to the oustside of the windscreen so I can safely monitor the pressure while driving. On the X-308, testing fuel pressure is relatively easy since there is an installed schraeder valve.

 

Spakenzap
Any chance of pic showing your fuel gage hook up with details .
also location of schrader fitting

Txs

 

You *could* change out to a stock filter and see if that makes a difference.

 

I agree with DSnyder: the K&N air filters have a coating that has been known to screw up 4.2 engine MAF sensors in both Land Rovers and Range Rovers (more so in my RRS/SC). Cleaned the the MAF and went back to standard air filter and the engine smoothed out.

It would be interesting to know what the humidity, temperature, and barometric pressure differences were when the car ran super and when it ran so, so.

 

A stock clean paper filter will not rob you of any power on a stock car. It is a very cheap and easy thing to do. Won't hurt, may help.

 

Thanks for all the replies Guys,

I will change out the K&N filter and report back.

We've had quite a warm summer here in the UK, but nothing really to write home about. We generally have a old and damp Autumn, so let's see what this brings.

 

Well Gents, I have changed out the K&N filter for the standard OEM paper one and things are much improved. I will keep monitoring, but all looks good so far. Thanks for the advise.