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E51 The E51 Catalytic Converter Problem

Chris T

Here for life
Premium Member
E51 Owner
Wales
Thanks - and Ouch! that's quite the price - haven't looked under the car yet but assuming I'd need 2 of these?
Both pipes you need are in that kit. It's expensive and maybe a local exhaust place could make it up cheaper, but if you're looking to take it to a garage it will probably be cheaper and easier to get the garage to decore.

The advantage with those replacement pipes is someone with minimum tools and skill can swap them in their drive.
 

BigAndy1979

Active Member
E51 Owner
South West
yep, going for the cheaper option of de-cating, booked in for next week.

Have a good Powerflow exhaust place in Hove that done my Merc 190E Cosworth about 12 years ago so if I was going to spend £££'s would probably opt for them to do it. I just want rid of the potential problem rather than any BHP/sound gains.
 

Phil

Part of the furniture
Premium Member
E51 Owner
the only advantage of the kit is that you know for definite that the cats have been done. I'm not saying all garage services are dodgy but I wonder how many people are running around thinking their rear cats have been decored when they haven't?

Edit. And they are easy diy for the occasional home mechanic. So that's 2 advantages then :)
 

Archies Gang

Newbie
E51 Owner
Scotland
Just carried out a secondary cat decore on Snow White today was so :worried: about this issue.
off side cat not a problem(Long pipe side) cut open as describe in the forums and re-welded:D
sheared 2 of the studs on the offside cat :oops: had to drill out:relieved: and fit 2 bolts.
to save cutting and welding this side is it is easy to smash the core out :grinning:

Now Snow White is singing a sweet song and now i can rest happy it ain't gonna go bang :D
 

Highway Dave

Well-Known Member
Premium Member
E51 Owner
Yorkshire
OK ,so just took the heat shields off (lifted them to gain access)---nothing apparent on the short one but what feels like a line of weld (very smooth if so) on the longer one, so i'm really no wiser as they both sound the same if I tap with a spanner (not dull but don't ring out so to speak--in fact i'd say they sound like hitting a normal section of exhaust--I suppose i'm going to have to have them looked at
two questions first
1; my elgand E51 2.5 has over 92 k in miles (would cats have gone before this ???
2; Is it as big a problem with the 2.5 as it is with the 3.5 given the differences between the two engines build wise and compression wise etc
 

Karl

The Boss
Staff member
E50 Owner
Premium Member
E50 Expert
North East
@Highway Dave - the engine makes no difference. The problem is relevant to any car with pre and post cats in an exhaust system.

If they sound hollow, then chances are they have been done. I would remove the easier of the two pipes (the straight one) and have a look. If it's clear, and it makes the same sound when you hit it as the other one, then they have both been done.

For peace of mind, you could check the other one by sticking a length of hose pipe through it. If it goes all the way through, then there is nothing in there.
 

E51ZRider

Club Rep - South East
Staff member
Premium Member
E51 Owner
South East
Thanks - and Ouch! that's quite the price - haven't looked under the car yet but assuming I'd need 2 of these?

Edit =- just realised it's for both pipes, so not so much ouch!
I have those on mine and its peace of mind.,..any issued rebolt cats for MOT...
 

Highway Dave

Well-Known Member
Premium Member
E51 Owner
Yorkshire
@Highway Dave - the engine makes no difference. The problem is relevant to any car with pre and post cats in an exhaust system.

If they sound hollow, then chances are they have been done. I would remove the easier of the two pipes (the straight one) and have a look. If it's clear, and it makes the same sound when you hit it as the other one, then they have both been done.

For peace of mind, you could check the other one by sticking a length of hose pipe through it. If it goes all the way through, then there is nothing in there.
I know what your saying mate and I know it makes sense-----it's just that if I take the exhaust off myself I just know i'm going to end up putting something else back on ,i'e stainless---not because they need it, just because lol
 

skyrider

Member
E51 Owner
South East
if you have your cats replaced keep the old ones and have them clean out in your own time then if your Elgrand fail the mot because they are missing you can put them back on
 

GNDTECH

Newbie
Premium Member
E51 Owner
THIS IS NOT FORUM LORE. THIS IS NOT A MYTH. THERE HAVE BEEN MANY DOCUMENTED INCIDENTS WHERE OWNERS HAVE HAD THEIR ENGINE BLOW UP BECAUSE OF THIS ISSUE. YOU HAVE BEEN WARNED.

CHECK OUT THIS THREAD FOR PROOF

LIST OF AFFECTED MEMBERS

The problem

A widely known issue with the Nissan Elgrand E51 is that the rear cats get blocked causing catastrophic
damage to the engine.

The problem starts with the fact that the E51 has a QUAD CAT SYSTEM. This means there is a PRIMARY and a SECONDARY catalytic converter on EACH BANK of the V6 engine.

The PRIMARY cats are the problem. Through use, after heating up and cooling down, they start to deteriorate. This happens with ANY catalytic converter when they reach the end of the their life. As the PRIMARY cats starts to break down and fall apart, the debris is pushed back through the exhaust. At this point, they come into contact with the SECONDARY cats, which creates a blockage.

As more and more of the PRIMARY falls apart, the blockage will prevent any exhaust gasses getting out. The exhaust gases (and dust particles) then build up pressure and go to the only place they can, back into the engine. It doesn't take a mechanic to know that if you put exhaust gas mixed with catalytic converter debris back into an engine, it's not going to last long.

So, that covers the problem, what can you do about it?

There are 2 main options.

1/ DECORE the SECONDARY CATS. This is a simple process. You remove the secondary cats, cut an opening in the top, smash the internals out, weld the opening shut again and re-fit them. This removes the point at which the debris from the PRIMARY cats will get stuck creating a blockage. The debris is just pushed out the back of the exhaust.

2/ Remove the SECONDARY CATS. Same principle as option 1, but you remove the cats altogether and replace with a straight through pipe. This is more costly than option 1, BUT what it means is that when it comes to MOT time, you still have the cats to fit to the vehicle if there are ever any issues.

But what about.......?

You will fail an MOT if you remove the rear cats and the tester knows they should be there. So if you do fit straight through pipes, keep the cats and then you can fit them again at a later date if you need to.
If you go for option 1, make sure the access hole is cut in the top of the cat so that the head shield will cover the weld when it's sealed up again. If the hole is on the bottom, and the tester can see that they have been tampered with, he'll fail it.

Emissions are NOT affected by removal of the secondary cats. They are only part of the system due to the strict "cold starting" emissions policies in Japan. In the UK the emissions test is done on a warm engine, and therefore the secondary cats serve ZERO purpose.

Is this legal?

I don't know what PC Plod can do about you removing/modifying the cats. But, if you tell an MOT tester that you have modified the cats in any way, and it fails, then technically the car is not road worthy. We know this is bollocks. It'll still pass the emissions test, it will still drive perfectly OK, and you have removed the risk of having your engine blow up when belting down the motorway at no more than 70 (of course).

The choice on what you do is up to you. Keep them if you want. But then every time you drive your E51 you will be wondering when the engine is going to blow up. I know from a personal point of view, I'd rather take the risk with the MOT tester than have catastrophic engine failure and a £4500 engine rebuild bill.

I heard about a Recall for this problem!?

The recall has NOTHING to do with this problem. All it will do is prolong the inevitable. The recall was put out to adjust the fuelling. If your car is subject to the recall, the engine map was putting too much fuel into the engine. This meant that excess fuel was getting blown out of the engine following combustion and then igniting in the exhaust system due to the heat. This meant that the exhaust was getting a lot hotter than it should causing premature deterioration of the primary cats.
With the recall in place, the engine will not overfuel... but it does not mean that the primary cats will not start to disintegrate over time.

There have been at least 2 instances that I know of where a car that was NOT on the recall list has had the engine fail because of blocked cats.

Why does this need doing?

Cars built for EU and UK roads are designed with the climate in mind. Therefore, as part of the manufacture process, there are treatments applied to the bare metal to prevent the chassis corroding. JDM cars are NOT done, because the climate in Japan is very different to ours.

The underseal is required to ensure that your car doesn't turn into a pile of rust over the winter. More importantly, because you are doing this AFTERMARKET, it is something that is seen as temporary, not permanent. The products applied will, over time, wear off or get damaged thus leaving untreated metal to come into contact with salt and moisture.

The better the product you use, the longer it's life. There may even be products out there that come with a "life of the car guarantee"... but I'm sure they'll cost more than £400!

With that in mind, discuss the options available with the garage you chose for your underseal and discuss repeat applications and how often they will be required. If they want your continued business, they will offer all options and tailor the service to your requirements and budget.
Spend the 400
 

Highway Dave

Well-Known Member
Premium Member
E51 Owner
Yorkshire
@Highway Dave -

For peace of mind, you could check the other one by sticking a length of hose pipe through it. If it goes all the way through, then there is nothing in there.
Wow---just realised what you said karl-----not only are the Elgrands good looking,powerfull,quick(going on fast),reliable etc etc, but now you tell me they can also take a length of hosepipe without ill effect------thinking seriousely of sacking her indoors now :):rolleyes:
 

Chris T

Here for life
Premium Member
E51 Owner
Wales
Hi there,
Was the £90 to remove both rear cats, cut open the top remove the insides and re-weld?
My 2003 E51 done about 88000kms so maybe I should have the job done.
regards
jackh
There's no maybe, have it done mate, they will fail in the end. We've had a member today have a lucky escape due to partially blocked cats. It's not worth the risk at all for £100.
 
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