MOT Fail - Emissions - Probably Cats
 

Hi There,

4.2 V8 Petrol ~162,000M


Just had an MOT.....Failed Emissions on CO on Idle, 2nd fast Idle, Fast idle and HC/Lamda on the fast Idle.

The Co points to the cats. I've had the Check Engine lights on for quite a while on both banks which I thought was odd (16814 & 16804)....I did try a few cleaners when I got the car, but since it's passed the two years previous MOTs I haven't been worried.

I've got some toluene so I may give that a go and see if it gets better, but I'm guessing it's a pair of new cats ???




Any help, pointers etc

Lee

If the lambda probes are not too expensive I would just replace those as it failed on fast idle lambda value / mixture.

Just had a play with VCDS

I'd cleared the error code before the MOT, but i just did a readiness test and it passed everything apart from the Cats, so 0000 0001

It seemed to think the sensors with the aging test was ok

Blocks 46 and 47 read Cat 0.13 and 0.19

I've got some Toluene and half a tank of gas, so i'll go for a drive and see if I get any real change.

I had a cat issue with an Rx8 I have and on swapping, found the housing empty....Am wondering with an inspection camera if you could feed it down the exhaust or maybe break the pipe and do a visual inspection???

I agree as it failed lambda as well it's more likely to be first lambda sensors or possibly air leak. Have a look at values for lambda voltage in measuring blocks with VCDS. They should be changing quite sharply between approximately 0.2-0.7V about once per second. If there is no activity, smaller range or slow to respond then it/they are faulty. But if you keep driving with faulty lambdas for long time that will eventually damage cats.

Looking at the MOT they'd tested it on Petrol. Retest on LPG and that's the MOT sorted.
However the LPG runs rough and having been through the system, plugs and coil packs, I have a feeling the sensors may be having an effect there, so i'm going to have to do some investigation there, but at least it's not the CATs. Workshop guide for the garage was say 12.5hrs for a cat and 13hrs for them both!!!

Can you post all gas readings off print out

Are pre cat Lamdas 5 wire wide band ?

What is short term fuel trim doing at idle and at say 2500 rpms

Mechcanico Lee

Bit confused on what you want, but happy to play!

I can hook up VCDS this afternoon and look the fuel trims, LPG or Petrol?

CO is fine on LPG, though HC is high, but just within the *MUCH* wider limits than on petrol and only until the LPG drops cylinder 8 though it also mentions 10??? It's only a V8

I think what is happening is that the post cat sensors being out is meaning that it's either under or over fueling causing the emissions issues and the LPG is trying to trim to such an extent the miss fires are happening!

Post cat lambdas is only there to monitor cats, they do not affect fuelling.
All lambdas are narrow band on D2.

ainarssems - It's a D3!

Hi There,

Just had a play with VCDS.

I ran the Readiness check (http://www.ross-tech.com/vcds/tour/readiness.php) Which checks various engine bits. The other day it passed all but the cats. Today it passed everything when going through, but the Evap showed fail too!
This checks the secondary air (vac??) and a few other bits. It seems to think the lamda sensor aging is fine though?

I cleared the engine faults so it clears the trims on block 032.

I ran it for a while checking through all the engine blocks and then checked again and ran 2520rpm

Block 01 - 2520rpm, temp 99c, Lamda1 -3.9%, Lamda2 2.3%
Block 02 - 2520rpm, Load 15%, Inj Time 2.46ms, MAF 18.36%

Block 032 -Idle (+) Partial (X) - B1 - Idle (+) Partial (X) - B2
1.3% -1.6% 0.4% -0.8%


I then thought i'd give the LPG a go and see what that did

Block 01 - 1120rpm, temp 102c, Lamda1 -18.8%, Lamda2 0%
Block 02 - 1120rpm, Load 15%, Inj Time 2.87ms, MAF 7.68%

Block 032 -Idle (+) Partial (X) - B1 - Idle (+) Partial (X) - B2
1.3% -18.8% 0.4% -0.8%

Also got

16684 Random Misfire P0300
16692 - Cylinder 8 P0308Misfire
17718 - Cyl 10 Ignition circuit - P1310 short to ground
17536 - P1128 System too lean


BTW - I got the 5/8 coils swapped by audi under warranty, I then swapped the last 3 so it had new coils. I've also tried two complete set of spark plugs.

I took it to an LPG guy and he played and swapped LPG injectors - I do also have the Zenit LPG software and can do some things in there, however the conclusion of the process that it seemed to be the car shutting things down and I just never got it to the point it would do anything but the above style faults. IIRC the cylinder that shuts down varies too!

Has your LPG software ever been properly mapped to the car Lee? mine kept throwing up "too lean" faults until the LPG company had tweaked its software a couple of times and it gradually got better until it went and has never returned since - worth a look

Architex_mA8tey - I've got the software myself. Alas the company that did the install (~10 months before i got the car) are in Poland which makes thing interesting in terms of having a word or popping over!

It's a pretty good kit from what i've read and quite well specified. I've re-routed the odd pipe and cable which I was less happy with but never found anything that was a show stopper. The LPG guy I took it too also checked it over but wasn't a Zenit

I've tried the adaptation routines and can get it to work, but the dropping cylinders makes it difficult etc

I'll get my coat

Woooo, I've pulled!!!.....Oh wait!

Post the 4 gas readings from the mot gas tester report

The pre-cat O2 sensors on the BFM engine are 5-wire widebands if this is still relevant, I did mine last year. They were around £40 each (Bosch) shipped from USA, much cheaper than over here.

I think I had to remove the intake manifold. One side was fairly easy to swap but the other one was almost inaccessible. It took me a few days to finish the job in the end as I dropped my lambda socket somewhere behind the engine and couldn't find it. I think it's still in there now!

Mechcanico Lee

Petrol - Fail
-----
Fast idle
Co 0.54% vs 0.3%
HC 208ppm vol vs 200ppm
L 1.056 vs 0.970 <> 1.030

2nd Fast idle
Co 0.84% vs 0.3%
HC 121ppm vol vs 200ppm
L 1.015 vs 0.970 <> 1.030

Natural idle
Co 0.53% vs 0.5%
-----

LPG - Pass
Co 0.55% vs 3.5%
HC 804ppm vol vs 1200ppm


MatthewH - Interesting. How and where ???

On the first fast idle the lamda reading fails ....but it’s failing only slightly and toward the lean side

On the second fast idle the lamda reading is a pass

Don’t confuse the lamda gas reading with the lamda sensors .....it’s often done

The lamda gas reading would be better off called mixture strength, lamda 1 or stoicimeteric 14.7 to 1 the ideal mixture strength .

If a car passes on the lamda reading this means the mixture strength is correct so any co and hc failings are because the cats are not doing there conversion .

Looks like the vcds readiness tests are bob on .

I have heard of this thinners thing in the fuel and if it works so be it , it’s worth a go , don’t buy cheap after market cats , they are rubbish with nowhere near the precious metals and rhodium of genuines .

If you are friendly with your Mot station often a good scragging up the road get the cats really hot then get it straight on the gas tester often gets the Co and hc down

+1 on aftermarket cats - the market is dominated by incredibly poor quality parts (I did some work investigating this in my previous job, with a view to instigating a change in legislation which hasn't yet happened)

I found a company in Germany that will refurbish your cats with metal substrate rather than ceramic and turn around time was pretty good. Germany has a higher level emissions test and their market isn't overly dominated by crap product - any product marked Blauer Engel (Blue Angel) meets that higher standard but supply of A8 aftermarket products is pretty limited and I've not checked what's out there for the D3.

Details are in this thread:

http://forum.a8parts.co.uk/showthrea...highlight=cats

I priced up OEM D2 cats and they were about £1k each, so a good saving if you assume that all cats will fail sooner rather than later.

Adrian

The after market oddly don't seem to do anything for the D3 4.2 petrol that i've found. I know they are far less reliable anyway.

There's an argument of getting a decent cat for elsewhere and welding it into place!

However i'm currently looking at getting the LPG working properly as that's something more useful in the long term and something I should have done a while back. I've just tried swapping the MAF (bosch) and will give the LPG software another play.

Initially getting Cylinder 8 missfires though!

There's a thread here (different car)
https://www.pistonheads.com/gassing/...&f=23&t=866609

Which mentions different gappings for gas which may be something to look at

And another which also mentions about the HT spark leads may be an issue with arcing due to the higher specs
https://www.pistonheads.com/gassing/...&f=69&t=906093

Which also may be something to look at