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Trisman

Blocked Cats..... (On an E39 523i).

7 posts in this topic

Firstly, does anyone know if this is something that 523i cars are prone to?

(Symptoms are massively reduced performance, no power above a couple of thousand revs, otherwise the engine runs just fine, starts well, idles nicely, no overheating...).

The original Cat was a single, siamesed-entry affair, unlike the twin Cats on the 2.8 M52 engined cars...

(Apparently..) The car in question was overfilled with oil & somehow, that got into the Cat, blocking & pretty effectively wreaking it? That's the theory anyway, though I'm not exactly sure HOW the oil would have got into the exhaust. It's not a diesel!

The car has now had the front portion of a 528i exhaust fitted. This seemed to cure the problem, but occasionally, it still does the lethargic performance thing.

When the exhaust was disconnected to confirm the blocked cat theory, it ran fine, if a little noisy...!

My theory is that there is still some crap in the exhaust blocking it further down the system.

Any thoughts or experience of this? (...DunCAN!).

Edited by Trisman

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Maybe yours is too blocked but I've used Cataclean in the past to keep the cats in good nick

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Well I know of a 523i that blocked it's cat. It was a bang and a rattle. Ran fine but wouldn't pull more than 45! New cat and it was fine.

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^ ^ No bang, (I got it with the problem) but sounds similar otherwise.

It'd get up to 60~ish eventually, but I had to use the gearbox in manual mode & kinds 'row' it along.

It's better now, but sometimes seems to run out of puff.

Away from rest, I can get the ASC light to flicker, couldn't before....

Course, if the replacement cats are also blocked.... :(

Shame, cos it's quite a nice car.

An 'S' reg Oxford Green Touring, one owner, massive history and... Proper springs on the back!! (No self-leveling to go tits-up!).

Back on the ramp on Monday....

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My cat blocked on my 523i..

In fact the inner monolith detached and spun..Partially blocking the exhaust and then reduced performance.

Drop th exhaust off and smash out the monolith with a long bar and a hammer.

Happy days!

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I used to buy a cat cleaner before every MOT and to my mind it worked. Then I read a report on them that basically said you would be better off buying the higher priced unleaded at the pump. Higher Octane? When you pull up the pump you have a choice of two unleaded's just fill it up with the higher priced one and it does the same job. But the advantage of course is that you are getting petrol with your cat cleaner, as opposed to just spending £20 on a good cat cleaner.

At one time I also poured redX, showing my age now, into the carb and it gave out a satisfying cloud of smoke out of the exhaust supposidly it cleared sticking valves and cleaned out gunk from the cats. I am sure many older members on here will remember trying this trick.

Just a couple of extra things to try. Hope it helps.

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It'd get up to 60~ish eventually, but I had to use the gearbox in manual mode & kinds 'row' it along.

It's better now, but sometimes seems to run out of puff.

Yeh I found using tip and keeping the revs low allowed me to get home after the AA man punctured the cat for me. Mine was definitely fubared!

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