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Robert, UK Qualified Car Technician
Category: Jaguar
Satisfied Customers: 4716
Experience:  Fully qualified / self employed garage technician in the UK
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I have a 2006 XJ 2.7 diesel. Just had the cats replaced because

Customer Question

I have a 2006 XJ 2.7 diesel. Just had the cats replaced because of splits in the cat tail pipes. Took it to a non-main dealer who fitted a pair of used cats for £1000 instead of the £2150 quoted for a new pair by the main dealer. When picking the car up I noticed a mild rough throaty noise when lightly decelerating down from about 25 miles per hour, and very occasionally a similar noise when accelerating. The garage said the noise will probably disappear when the cats are sooted up. The problem is that there was no noise at all before and I no longer have confidence in the garage because they had to keep it 2 days instead of the quoted 1 day, said the bolts sheared so they had to re-tap the turbo and also fit non-Lambda sensors (whatever that means). They say it took 2 days instead of the 5 hours quoted but only charged me for 10 hours. they also said the diff pinion oils seal was leaking (which it is, having looked at it) but the main dealer didn't point this out on its service 3 weeks ago.

Why should this noise appear at the same time I get the car back and am I being too cautious with my loss of confidence in them? I feel like either getting the main dealer to do it all again or just getting rid of the car.
Submitted: 4 years ago.
Category: Jaguar
Expert:  Robert replied 4 years ago.

Hi..there sorry for delay..


Just to clarify - Where exactly did these used cats come from or was these sourced off another car of around the same year etc?


How does the car perform in general terms apart from the issue you have?


Any warning lights as such come since this was done?



Customer: replied 4 years ago.

The garage told me they came of a Jaguar 2.7 diesel, either an S-Type or an XJ which have identical DPF cats as can be seen if you compare the ones taken off with the ones now fitted. they also said that they came off a vehicle which had 4200 miles on the clock. My car has 53,000 miles on the clock.


The performance is the same although I suspect the turbo boost, which is delayed on these engines as you know, doesn't have as much power but i can't be sure. There again, the garage said that they had put an additive in the diesel for me. i hadn't asked for it, I don't know what it was and it already had Shell V-Power diesel in (as it always has).


The noise is worse today and now occurs when you are cruising at 25 - 30 mph with slightly varying speed.


No warning lights have come on since the job was done.

Expert:  Robert replied 4 years ago.

Hi..there thanks for getting back..


Usually new fitment exhausts/cats can tend to be louder or the engine sounding more deeper as appossed to a well used system due to the internals needing time to soot up as they say - in turn through time will become quiter in operation once the system is coated - if they had come straight off a car then you would suspect these cats to be already coated internally unless they where cleaned/cleared before hand..especially with low mileage deisels or diesel not often used as much these do tend to soot up quite heavily since the they dont get a change to heat up properly to burn off or reduce the amount of soot building up so there maybe possibily of them being maybe partically blocked and thus a restriction in not say thats for sure - but its something to bear in mind especially with second hand units as it hard to tell what the internals are like or the car they came off from previous use other cause could be fitting error maybe at the joints/connection between the two cats etc. maybe blowing slightly and thus you may hear that sort of noise around that rev maybe if you can have look and listen to see if can hear any blowing as such from the joints at either end of the cat converters aswell as where they had to re tap and replace the studs at the turbo end etc also too maybe check the rest of the system just to be sure there isnt any splits formed during the removal and fitting - that can often happen ..its not uncommon to break studs on exhaust systems as they are prone to extreme heat and then cooling and then exteme heat again aswell as the eliments so that may have been ineveitable anyway and may have been issue with if it had gone to the dealer instead...and additive is really only for injection system clear out deposits and such like as such to reduce black smoke etc but most top brand deisels such as you using via shell already have such additives to help with that..If it sounding worse today then its it possible it maybe the cats or fitment error as such..its certainly something due to the costs involved to have the fitting garage actually investigate this further,especially so if the problem has become more noticable or is becoming more of a noise issue i shouldnt see them having any problem try to trace this down - rather than going straight to the dealer since they will just fit new ones at the cost you where quoted aswell as the their fitting cost ontop,one alternative would be to get second "visual/listening" opinion from the dealer might be one option..I do hope this helps