Hi,

I have had the dreaded Restricted Performance light coming on occasionally for over a year on my 2007 XJ TDVI Sport Premium - only normally about once a month and if you power it down for a couple of minutes it would go away for a few weeks before coming on again.
Over the last couple of months however it was coming on every day, on each journey to and from work... at about the same place on each journey too!

Finally got fed up of it and sent the car into a pal of mine who is an auto electrician and garage owner to sort out... fearing the worst - turbo issue / inter-cooler fault etc... etc...

After some diagnosis, which was a bit tricky as Jag's are not the easiest of things to diagnose accurately even with pro software, it turned out that I had an faulty EGR valve, he could not pin point which one was faulty though.

The solution he recommended was to remove the EGR valves and blank them off and write them out of the map, re-mapping the performance side of the engine too.
Turns out that EGR valves that are not working to best capacity are bad for emissions as well as the emissions test for mine actually has the car as running cleaner after they have been removed compared to the last MOT on November of 2017.

So far I am approx 6 weeks in and the RP light is nowhere to be seen, fuel economy is up, only slightly in the real world mind you, I wouldn't believe the hype of a 10 - 15% increase, and the performance is improved as well in the mid range due to the increase in torque.

Not going to be a solution for everyone as the RP light can be a royal pain in the **** to sort out but in this case it has been sorted - cost about £300 to have the whole job done which is WAY cheaper than replacing the EGR valves!

Always worth an ask if you are having the same issues....?

 

It's illegal, though.

Plus, you must tell your insurer you made a modification...

 

+1 on both those.

Actually in the UK the only emissions parameter currently tested on diesels is particulates, ie smoke; NOx emissions limits, although specified in the various Euro emissions classes, aren't currently tested. They are for petrol (gasoline) engines.

EGRs are fitted to both petrol and diesel engines (but especially to diesels) to reduce NOx emissions. By blanking off the EGRs you will reduce the particulates produced by the engine, but that's pointless because they are all trapped by the DPF anyway. More importantly what you will also do is raise the NOx emissions (on which the DPF has no effect whatever) and you'll almost certainly put the car above the Euro-4 limits, which is what it's designed to comply with.

Moreover, if NOx levels do become part of future MOT tests for diesels (as they well may) then your car will almost certainly fail.

 

As EGR reduces knock, removing it will also affect timing.

 

On a petrol engine, yes; on a diesel, I'm not sure. Diesel knock is mainly controlled by pilot injection ? And for sure on on the 350 by using two-state (electrically controlled) engine mounts to isolate the engine from the frame at both low/idle revs and higher revs.

EDIT: But then of course if there were timing issues then surely the remap would have fixed that ... ... of course ... maybe ... possibly ... perhaps

 

It can't restore the knock effect of the EGR if you've made the illegal change you posted.