Catalytic converter - AJ16 4.0L

[Tintin]

How can I tell if my downpipes are fitted with catalytic converters or not? Both catalyst and non catalyst versions are listed for the car. The only visual difference in the diagrams is that the catalyst version seems to be fitted with a heat shield attached where the two pipes join into one but the non catalyst version isn't. Is that definitive?

My problem is that the downpipe has fractured on the line of a circumferential weld and I need to make a decision on repair/replacement.

Thanks

Robbie

[davidr]

I think it almost certainly will be. The give away will be lambda sensors

[Tintin]

Thanks, David. I thought it would be simple to identify when you knew what to look for.

Robbie

[ptjs1]

Robbie,

If the pipe has fractured its weld at the usual place (ie where the two downpipes are crimped and then a small "collector" pipe is welded to them which then creates a single pipe that goes to a slip joint) then I'd strongly suggest that you remove the pipe and just get it re-welded at that point. That "Crimp & Join" is not a great piece of engineering.

I had the same problem on my car back in 2006 and I published the issue with photos in the magazine at the time. New pipes then were £1000 and are now unavailable anyway! The cats last a very long time also so repair is quite a realistic option. I paid a garage £30 to rerun the seam around that joint. All you need to do is gently cut off the last 3" of the heatshield and then you can access the weld point. You can see from the second pic below exactly where to cut the heatshield on the "G" of JAGUAR. You can then just tack the remaining heatshield to the pipe or frankly, just leave it as it is. Try and get the car up a bit in the air. I managed to wiggle the pipe out with the car just on car ramps but it's a bit of a pain.

Whilst the pipe is out, it's a good time to change the downpipe studs, clean up the slip sleeve attachment at the downstream end and also change the lambdas if they are more than 5 years old. Disconnect the lambdas at the wiring plugs anyway in order to remove the pipe, then take the lambdas out when the pipe is out and they are much more accessible.

Good luck

Paul

[Tintin]

Thanks, Paul - you are spot on and your very comprehensive guide will be most helpful.

Looking at the downpipe and heat shield again it is already as your picture No 2 so I suspect a previous owner has already had the welding done - and probably in situ without taking the pipe out. I say this because looking at the top surface of the pipe with a mirror and torch, the weld is incomplete along the line of the fracture (and very rough along the other 75% of the join). I will retain the catalyst, re-weld the joint out of the car and replace the studs and lambdas as suggested.

Robbie

[ptjs1]

Robbie,

I can understand why someone would try and do it in situ but I think you'd need a really good welder to be able to get all the way around without melting things! Once it's off, it's quite easy to do a good job on the pipe.

I'm glad that my experience may be of some little help to you. From memory, the most awkward item is trying to remove one or two of the downpipe to manifold nuts. There is (at least) one of the inside ones that is difficult to access. Going from underneath, I used two extension bars and a wobble bar plus lots of penetrating fluid and finally did it. Go carefully, it can be easy to shear those studs. The manifold to downpipe gaskets are NLA but don't tend to rot that easy so you be able to clean them up ok.

At the risk of increasing your bill, it's also the best time to have a look at the manifolds and see if you have the expected micro-crack in either of them. As you probably know, this usually manifests itself as a slight chuffing sound on startup that disappears within 30 secs as the crack warms up and seals. I have heard anectodally of people who have welded them but frankly I'm not sure if that's actually possible. Again go easy on those nuts and studs if you take the manifolds off.

TOP TIP: Very carefully photograph and mark the orientation of the two lambda sensor plugs before disconnecting! It's so easy to get them mixed up!!

Cheers

Paul