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E51 The E51 Catalytic Converter Problem

Most people leave the front cats as they are & decore or remove the rear cats. That way if/when the front cats break down the crap is able to escape out the back.

My fronts have done exactly that and despite the rears being non existent, the debris on the passenger side seem to be causing back pressure. Driver's side has been long gone.
 
To anyone inthe know or those who have had near misses as a result of the front Cats collapsing could you please give me a rough idea of costs for decoring or indeed the best way to approach the matter and associated costs. This is perhaps a subject of a new thread but There isn't much detailed info associated with front cats failure or indeed remedying the issue, Be it an emergency, short term or long term solution. Any pointers would be appreciated.

The struggle is real.

I replace the rears with factory sections that have been de-cored, refurbished and vht protected, on an exchange basis, while you wait or mail order.
D9B3E6BC-E860-4D48-B8A0-996D202DFE28.jpeg
 
I replace the rears with factory sections that have been de-cored, refurbished and vht protected, on an exchange basis, while you wait or mail order.
View attachment 10032

Thanks for the reply but my issue right now lies with a collapsed front cat causing back-pressure even though I do not have rear cats.
 
Just out of interest, has anyone replaced or removed front cats. Is it one of those "should be simple, but probably isn´t" jobs, like replacing the spark plugs?
 
Just out of interest, has anyone replaced or removed front cats. Is it one of those "should be simple, but probably isn´t" jobs, like replacing the spark plugs?
I've seen it mentioned somewhere on the forum. Having a rubbish memory means I forget where. It may even have been in this very thread.
 
Just out of interest, has anyone replaced or removed front cats. Is it one of those "should be simple, but probably isn´t" jobs, like replacing the spark plugs?

I did, decored only. Didn`t touch rears as they not issue on E51. 4 hour labour in garage. Done spark plugs myself in less than 2 hours.
 
I did, decored only. Didn`t touch rears as they not issue on E51. 4 hour labour in garage. Done spark plugs myself in less than 2 hours.
Well done with the spark plugs. Did you follow the Australian guy´s you tube video?
 
My fronts have done exactly that and despite the rears being non existent, the debris on the passenger side seem to be causing back pressure. Driver's side has been long gone.

This is a possibility I've been meaning to mention on this thread for a while....

Vehicles that don't have cats in series (most vehicles just have one cat, especially inline 4 engines) can still suffer blocked cat issues if the cat fails... But most often when a cat fails (that isn't in series with another cat) the debris doesn't lead to clogging or back pressure because the debris just gets blown out the exhaust. Where-as if the front cat fails in a series setup it is almost inevitable that the debris will then clog the entrance to the rear cat and will cause back pressure.
 
I did, decored only. Didn`t touch rears as they not issue on E51. 4 hour labour in garage. Done spark plugs myself in less than 2 hours.
Any heads up on how this was done would be appreciated. I can then pass this info on to the garage. There is also talk of oxygen sensors and spacers etc..how did you get around this and are you still okay with MOT with just rears?? I will probably go down the route you took and replace rears instead. That's if the Engine hasn't been fried already.
 
This is a possibility I've been meaning to mention on this thread for a while....

Vehicles that don't have cats in series (most vehicles just have one cat, especially inline 4 engines) can still suffer blocked cat issues if the cat fails... But most often when a cat fails (that isn't in series with another cat) the debris doesn't lead to clogging or back pressure because the debris just gets blown out the exhaust. Where-as if the front cat fails in a series setup it is almost inevitable that the debris will then clog the entrance to the rear cat and will cause back pressure.

Well put...I feel this is the elephant in the room on our forum. Maybe it's just me but we are all decoring rears and hoping the problem goes away, unfortunately it doesn't. You may get lucky if the cat crumbles favourably and get blown out without any damage to your engine but as it's turning out for me, there is no guarantee.
 
Well put...I feel this is the elephant in the room on our forum. Maybe it's just me but we are all decoring rears and hoping the problem goes away, unfortunately it doesn't. You may get lucky if the cat crumbles favourably and get blown out without any damage to your engine but as it's turning out for me, there is no guarantee.
I'd say decoring rear cats does makes sense... far easier to do than decoring fronts (and of course far easier than a total decore of both fronts and rears). In the event of front cat failure (and perhaps I should say 'on balance') this will usually prevent the worst outcome but not in all cases. In a minority of cases the front cats will blog themselves up... as has happened to you. 'On balance' because it's unlikely a cat will blog itself up to same extent as a cat breaking up where the debris then has to pass through something that acts like a filter/sieve (entrance to second cat in a series).

I agree with you though that this is an elephant in the room and should be discussed, we decore rear cats because front cats break up so it is front cats that are the problem. Any vehicle that has a blown cat, even if only the one cat is fitted, can have severe exhaust restriction issues and can suffer all the same nasty outcomes (cat debris making it's way into the engine).

My front cat broke on my Elgrand (passenger side engine bank), the debris then clogged the entrance to the second (rear) cat which hadn't failed. I now need to replace the engine because debris from the front cat made it's way into the engine. If I had decored rear cats the chances are that it would have prevented the engine failure because debris from the front cat would have been blown out the exhaust but that isn't certain... debris from the front cat breaking up could have blogged the exit to the front cat up (far less likely to debris blocking the entrance/sieve of the rear cat but possible and does happen on other vehicles. Now, even if I replace the engine, it would be madness not to remove what remains of the failed front cat.
 
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Removing the rear cats really is a good idea to prevent debris from the front ones clogging them up, but if the leading edge of the front cats breaks up they can / could block themselves. Therefore although removing the rear cats helps significantly, it doesn't fix the problem of the front cats breaking up.
 
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Removing the rear cats really is a good idea to prevent debris from the front ones clogging them up, but if the leading edge of the front cats breaks up they can could block themselves. Therefore although removing the rear cats helps significantly, it doesn't fix the problem of the front cats breaking up.
Nicely put mate, totally agree.
 
I want to have metal sport cats fitted to ours for the front as I too think they will be a problem.
I think decoring the rears has helped ours make torque earlier as it get on power off the traffic lights better. Thinking replacing the fronts with less restrictive ones would also help. It feels a lot better now and the rears were fine. Just too much restriction in the exhaust in general.
 
Any heads up on how this was done would be appreciated. I can then pass this info on to the garage. There is also talk of oxygen sensors and spacers etc..how did you get around this and are you still okay with MOT with just rears?? I will probably go down the route you took and replace rears instead. That's if the Engine hasn't been fried already.

MOT not a problem, as most other E51`s with decored rears have no cats at all. :)
That was over 4 years ago and my other half took car to garage.
Windscreen wipers and plastic surround were removed, something was done with radiator because charged for 2L of coolant
 
MOT not a problem, as most other E51`s with decored rears have no cats at all. :)
That was over 4 years ago and my other half took car to garage.
Windscreen wipers and plastic surround were removed, something was done with radiator because charged for 2L of coolant

O2 sensors removed and put back after decore. No EML light.
 
Hi Guys dose any one in the uk do the Elgrand E51 - Cat / Catalytic Converter Replacement Test Pipes as in the last post above
Cheers
 
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