E51 MOT fail on CO ***free decat pipes***

AlanR

Newbie
E51 Owner
#1
Hi All,
I've had a new engine in my E51 after the usual cat problem (there was not so much info on the problem when it happened). I have nothing inside any of the cats now so it failed on CO. It was 0.9% when the limit is 0.3%.
I guess cats are required to pass the emission test.
I'm hoping it will pass with just the rear cats.
Does anyone want to swap my de-cored rear cats with some original ones? They have been cut open, contents removed and professionally welded back up. Could save someone some money on decat pipes and hopefully let my Elgrand pass on emissions.
I live near Middlesbrough.
 

MrRob_in

Part of the furniture (please de-cat your e51/2)
Staff member
Premium Member
E51 Expert
E51 Owner
#2
I must admit you are one of the first I’ve heard of to have this (perhaps expected) issue. This was one of the reasons on my first e51 in 2010 I decided to have the front cats de-cored. Unfortunately they had already filled the rears with crap but car still passed emissions at mot on petrol when we tested it. It then ran to 80k miles on LPG to about 160k miles and subsequent owners had emissions troubles at mot on petrol.

Have you tried any of the numerous engine cleaning products? Might be worth trying first. Given the number of front cat failures and rear de-cores there must be a large number of us driving and passing mot with no cores.
 

AlanR

Newbie
E51 Owner
#3
I thought it would be ok since I had not heard of this before. Do you have an emissions printout from your mot?
I have not tried cleaning products but it is so far over I doubt it would make much difference.
 

MrRob_in

Part of the furniture (please de-cat your e51/2)
Staff member
Premium Member
E51 Expert
E51 Owner
#4
I thought it would be ok since I had not heard of this before. Do you have an emissions printout from your mot?
I have not tried cleaning products but it is so far over I doubt it would make much difference.
Nope it wasn’t officially tested with no cores on petrol at all as I presented it running on LPG.
My current car has failing front cats and no cores ... I’ll see if I can find it’s last mot...
 

Biffo

Well-Known Member
Premium Member
E51 Owner
#5
One problem could be the recent driving history of your car, if it's only done local outings over the last few days, that can affect the emissions, due to a build up of soot etc. Go and take it somewhere that you can give it a good thrashing, make the engine work harder and it will burn out the soot etc from the cylinders. Then get it proper warm by going for a decent run of a few miles before taking it to the garage for another check, you want everything up to temp, not just the water, it will take a few miles to get the oil up to proper running temp.
If you don't believe me, go start it up find somewhere open, press the "power" button, and floor the accelerator, through the gears, look in the mirror to see the black shite that comes out of it.
 

nobby62

Well-Known Member
E51 Owner
#6
Hi All,
I've had a new engine in my E51 after the usual cat problem (there was not so much info on the problem when it happened). I have nothing inside any of the cats now so it failed on CO.....
I live near Middlesbrough.
Nothing inside rear and front cats?...then it will never pass.... most people remove the rears but leave the fronts which is all you need to pass emmissions.
 

MrRob_in

Part of the furniture (please de-cat your e51/2)
Staff member
Premium Member
E51 Expert
E51 Owner
#7
Nothing inside rear and front cats?...then it will never pass.... most people remove the rears but leave the fronts which is all you need to pass emmissions.
But front then de-core themselves without you noticing usually ... I’d expect more mot failures to be reported if no cores always = an emissions fail. (But perhaps only very small amounts of cat core left in front cats do enough?)
 

Karl

Founder
Staff member
E50 Owner
Premium Member
E50 Expert
#8
The rear cats will not do anything for the emissions test. They are for cold start up only.

You'll need to get new front cats from a breaker or something to get it to pass.

This isn't an issue if you are running LPG, as the emissions on LPG are a lot lower naturally.
 

stevemen

Here for life
Premium Member
E51 Owner
#9
Seems a few are coming over from japan with front cats already removed iv just posted about it on the blocked cats post.
Tell tale signs of front cat removal is the original spot welds on front cat heat shields have been removed and heat sheilds have been gas welded back together at the ends of the joins
Steve
Tojomotorsuk
 

MrRob_in

Part of the furniture (please de-cat your e51/2)
Staff member
Premium Member
E51 Expert
E51 Owner
#10
Seems a few are coming over from japan with front cats already removed iv just posted about it on the blocked cats post.
Tell tale signs of front cat removal is the original spot welds on front cat heat shields have been removed and heat sheilds have been gas welded back together at the ends of the joins
Steve
Tojomotorsuk
Yep this was reported on the old NING site a few years back.
 

AlanR

Newbie
E51 Owner
#12
I do put my foot to the floor every so often anyway. I thought the reason for checking it as hot as poss was so the cats are at a proper temperature which will not help in my case.
I'm wondering whether disconnecting the lambda sensors might help or maybe apply a voltage to make the car think it is running too rich. I'll borrow a combustion analyser from work and have a play.
Replacing the front cats would only be a temporary fix. I've already broken 2!
 

MrRob_in

Part of the furniture (please de-cat your e51/2)
Staff member
Premium Member
E51 Expert
E51 Owner
#13
So was it done by nissan in japan?
Points that way as they are all professionally done and all using exactly the same method
It was reported by guys that fitted my Lpg (and maintain all my vehicles) As them just not having cores when they went to de-core them on the cars they fitted Lpg to or repaired for customer fitters (Autogas 2000 in Thirsk) and a couple of other forum owner / members reported their cores were gone when they went to de-core / check in 2010-11

I’d guess de-catting has to be even more stealthy in Japan were all exhaust parts need to be their equivalent of type approved.
 

Brendan1969

Here for life
Premium Member
E51 Owner
#14
Hi All,
I've had a new engine in my E51 after the usual cat problem (there was not so much info on the problem when it happened). I have nothing inside any of the cats now so it failed on CO. It was 0.9% when the limit is 0.3%.
I guess cats are required to pass the emission test.
I'm hoping it will pass with just the rear cats.
Does anyone want to swap my de-cored rear cats with some original ones? They have been cut open, contents removed and professionally welded back up. Could save someone some money on decat pipes and hopefully let my Elgrand pass on emissions.
I live near Middlesbrough.
Buy a bottle of " cataclean " and add it to 1/4 of a tank of fuel and take it for a drive for 30 miles then present it for M.O.T. Its supposed to do the trick a treat or you could also look at " Terraclean " of the engine too as this produces awesome results.
 

AlanR

Newbie
E51 Owner
#16
Thanks for the suggestion but since there is no cat to clean I'm not sure whether it will help.
That would be great Phil. I would be interested to know whether others were tested to the same limits.
 

AlanR

Newbie
E51 Owner
#18
You scored 0.19% on CO so just passed. Your limit is 0.2% where mine is 0.3% for some reason Have you still got front cats?
Your HCs are much lower than mine (67 ppm).
I'm going to try new lambda sensors because when my cat failed I measured a back pressure of 1.5 bar on light revs. If that didn't harm then then the old engine was spraying oil through the exhaust which would do no good.
 

AlanR

Newbie
E51 Owner
#19
I found the printout from when I first imported it and it was 0.07% CO and 3ppm HC but that was with all cats in place
 

Phil

Here for life
Premium Member
E51 Owner
#20
As far as I know the front cats are still intact but I've got a rear decat set fitted so nothing at rear. I don't really understand the data to be honest but it would be interesting if others could post their print outs as a reference or have any comments that might help you out Alan