How long should a cat last?

[Rallyman]

My daily drive 1.8 TQS has been getting a little sick - needing some TLC tots of turbo noise been a bit like it for a while... got a bit worse recently with a blowey spinney noise, and upset noise at 3-4k RPM so I drove it carefully I had been getting mixture adaptation ...gasket between turbo and had died.... Replaced it along with service etc... Turbo seemed ok but couldn't really check the cat though what I could see it was quite white - I not the "usual" honey comb texture you normally see.
Did a test drive the turbo got hotter than normal - cherry red and it didn't pull around 3-4k rpm as you normally expect it to... The cars completed 211,000 miles

I'm wondering if the CAT has passed its end of life and is blocked ? there are not any fault codes stored IS there any checked I can do to confirm..?

 

[aragorn]

are your tailpipes white?

Mine went white when the cat was blocked.

The blocked cat has probably blown the gasket out due to the back pressure.

Mine died at about 160k.

The monolith had broken into pieces and had fallen sideways into the bottom of the canister.

 

[Rallyman]

Ahh yes they have gone white - Thanks gooood to know!! Spoke to to Audi - 4b0254200AX is around the £700 mark

Found this one.... I hope there is a hole for the 02 sensor..... what's the NON OBD ?

Hopefully I have not killed the new turbo gasket as I cant find any one including Audi that keep them in stock - I have the lower gasket and bolts - phewph!

Fingers crossed the new CAT fits and that my old one there is some left to sell to the scrap man

What Boost should I be seeing as standard ?

 

[Rallyman]

Thinking about this, the turbo has got more noisy in the last few months, so this must been when it has started to fail!

 

[Oranoco]

My cat is original and the car has rolled past 170k. Mind you the cat has been in the garage for the last 30k

 

[Rallyman]

Lol ... I did think about "removing" it but it's probably doing something good ... :-/
I'll see if my replacement one does the trick....

 

[Rallyman]

Oh oh well old cat was toast
See picture....

 

[Rallyman]

But replacement cat - OE part number match - a bit different .... Will this make a difference on a TQS?

 

[Rallyman]

Picture

 

[Rallyman]

70mm compared to 62mm - is this right?

 

[aragorn]

Most of the aftermarket ones are pretty crap tbh.

Small and restrictive, and dont last that long. Not much you can do really.

Either stump up the big bucks for an Audi one, or maybe try to find a used Audi one, or fit the aftermarket one and live with it.

B6 1.8T uses the same cat so you might be able to find a newer one on ebay etc

 

[Bradderz_1988]

youll need a bung if you get a B6 cat for the downstream sensor.

 

[Rallyman]

Thats what the initial impression was of the after market cat.... I'm struggling to justify the ownership of the car to the other half :-( ... I had to get this turned around as its my daily drive ... There's a 2 year warranty on it - so if the engine goes on that long
Triggers broom springs to mind !!
If the monolith was removed from the housing would it still pass the Mot?

 

[aragorn]

No, it would fail on emissions.

TBH if its a standard engine the difference is likely pretty minimal.

 

[Rallyman]

Well it loads better now !!
What boost levels should I be seeing on a stock AJL engine ?
I'm begining to question the boost gage that I quickly chucked in last week it's been sitting around for ages 10+ years and can't see break 5psi under 4th gear WOT up a hill :-/

 

[aragorn]

5psi is actuator pressure.

Check for fault codes, somethings not happy!

you should see about 10-12psi

Maybe you've not plugged the N75 back in?

 

[Rallyman]

Boost gage is plugged in to the OE front inlet manifold front pipe near the alternator
No fault codes :-(
Is the N75 the 3way air solenoid ? I'll check it ..
Think I'll check the boost gage with the mityvac ....

 

[aragorn]

That front port goes to the dump-valve? Have you T'd into there?

Yeh the 3 way solenoid down on the turbo intake pipe. You could always unplug the N75 and see if you get less boost?

 

[Bradderz_1988]

Does it have a rattle on overrun ??

 

[Rallyman]

It's teed here
Ill check the n75 and the accuracy of the boost gage ... Tonight / tomorrow
On idle when I Rev it there is a rattle as the revs die down though don't think there's s pronounced one on lift off thou I'll check later

 

[aragorn]

Whats with the blue coolant hose?!

 

[Rallyman]

I had to replace the solid coolant pipe with a "flexi" to fit the LPG injectors underneath.
It's a liquid injection system so running the injectors as close as possible to the OE provides the best results

 

[Rallyman]

So what does the n75 do?

 

[aragorn]

It controls the boost.

The actuator on the turbo is rated at 5psi. That means it will open the wastegate when it "sees" 5psi and thus regulate the engines boost pressure to 5psi.

When the ECU wants more boost than that (usually 10-12ish at full throttle on a TQS), it uses the N75 to bleed off boost pressure from the line feeding the actuator on the turbo, and as a result the actuator holds the gate shut until a higher pressure is achieved.

When disconnected the N75 defaults to an "open" position, sending all of the engines boost to the actuator.

 

[PaulJC84]

Has anyone on here added an aftermarket cat just after the dp so it's easy to change out plus there are more universal ones available which would hopefully be better quality?

If I was added one back in I was thinking here would be best so I can get it put onto the 3" system.

 

[aragorn]

V6 cars have them there.

The issue is the close proximity of the gearbox and propshaft CV joint, and ground clearance. A 3" exhaust pipe already hangs below the chassis brace, and aftermarket cats are always round rather than the letterbox shape the OEM ones are made in to fit under there, so the cat would be hanging down an inch further still...

I recon the best way would be a VBand right behind the turbo flange, mount the cat there, then another vband after it just before it turns and drops down. Might be tight for space, but should just about be possible?