Mechanicists. Leak testing a catalytic convertor?

I’m getting an intermittent Engine Management Light. The code is to do with mismatch between the lambda sensors either end of the Cat. It only happens if the car is trickled along on the motorway for long periods – more adventurous driving and its fine. (it came up driving down to the Alps, then on the way back again. Thrashing round the cols it was faultfree)

It could be sensor error, or it could be a slight leak in the Cat body near the sensor (its a 20 year old car). With the engine running, I “think” I can feel a slight breeze on the back of my hand, but only slight and there’s so much noise and vibration under the car its difficult to determine much

I’ve got the cat off the car, the possible location of the leak is hidden from view by a welded on heat shield, so I figure some kind of pressure test is the way forward.

The easy solution will be to seal one end and fill it with water. Will this damage either the cat itself, or the lambda sensors? Plan B will be air pressure, but I’m not sure I can figure a way to seal both ends well enough for that AND attach a track pump!

Thanks

J

I’d use a smoke generator thingy (I’m not a mechanicist)

I don’t have a smoke machine at home (there are several in the warehouse at work, but that’s 160 miles away). I do have a tap or 2 though!

In true STW fashion of there might be someone that does it for a living ?

We do hot vibration durability testing of various dpf / scr systems. Pre and post leak tests are generally done with compressed air at 0.3 bar, measuring leakage rate with a little Festo flowmeter. You don’t care about leak rate, so bung up the outlet and carefully apply regulated pressure on the inlet from a compressor air tank. Anything significant can be easily spotted with leak spray or soapy water.

But I emphasis again you’ll need a pneumatic regulator and apply continuously and slowly 0.3 bar MAX. I am not responsible if you destroy it or yourself!

…mismatch between the lambda sensors either end of the Cat

Weigh the food in the bowl and check the litter tray later?

I’d figure on the flexibles on/near the cat starting to fail regardless. The flexibles are usually available separately from Autodoc to suit the car (I know as I’m planning on doing both of them on my Cayenne over winter). Obviously you need to drop the manifolds/exhaust and be able to TIG weld or replace the section with new.

@mick_r – Its figuring a way to seal the ends up to 0.3 bar that’s the bit I’m going to struggle with and how to then attach a compressor! On the other hand, if its not going to damage the contents – taping a bag over one end and filling it with water is easy!

@RustyNissanPrairie – no flexibles, the whole lot is rigidly mounted. (it’s not a front-engined car!)