X300: will car run OK without cat converter


1996 XJ6

I have a condition where the contents of the cat converter are loose, making a rattling noise.

If I remove and bash out the honeycomb, will the car run okay? Will the 02 sensors act up?


I removed all the cats on my XJ40 and the two under the car on the brothers X300 both ran very well without them.

Yep few weeks ago I gutted the cats on my 95’ XJ-S 4.0. The car will run with less restriction. If your car is latent to get to speed or if it seems to struggle when you hit the pedal it could be clogged or in your case loose and may also be blocking.

It will set off the check engine code without your cats(if it hadn’t already done so).

This is a picture of my cat with one hole drilled through it.(before I eventually removed it all)

Neither the XJ40 or X300 set codes in our case.

Thank you Robin and James.

I’ll bash away.


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It’s not easy. It was a lot of work to be honest. I actually cut the back side off and removed then welded it back together to make it more manageable.

Do you guys realise these cats are quite expensive? I mean, when it is clogged or rattly and you don’t have regular emissions checks that require working cats, I can understand why you would clear the cats out, but if it is OK and fully working, I wouldn’t recommend that. Why not replace it with a straight through pipe and sell the cat?
To be honest I am a bit scared of the day when I fail emissions testing due to a worn out cat. There are basically no original ones available because they all get sold for the (very high) scrap metal value.


I replaced our cats with bullet mufflers. And yes I sold the cats to a scrap merchant.

One difference you WILL notice with cats removed, your exhaust will be more smelly. Just think old 60s car smell. Not that pleasant when I’m idling with windows down and the wind suddenly shifts.

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I think you can have the innards replaced without losing the ABE and it will look the same. Don’t know what the price is.