Emissions ?

[Julian64]

How the hell does a 4.5 cerbera ever pass the emissions check on an MOT? Recently had mine MOT'ed. failed dismally. The check comes in two parts.
1) Natural Idle running 450-1500prm
2) Fast Idle. Car must stay between 2500 and 3000 rpm for 30secs.

At idle CO: was 0.41, fantastic. anything under 0.5 % vol gets through.
However at fast idle which was 2500-3000 (his MOT book listed 3000 for a cerbie 4.2 but the cerbie 4.5 was unlisted) CO: 0.01% and HC: 1049. To pass this had to be under 200!!! ppmvol and lambda 1.204 (0.970-1.030) Also a straight fail. Because he's quite a frendly chap he let me retest every rpm between 2 and 3 thousand to find if it COULD pass.

At this point I'm in tears, there is no way this cars ever gonna get through an emissions test and I'm wondering what the rest of you do.

Any ideas, then I'll let you know what happened next.
We need more suspense on this board.

Julian

[frodo bagins]

There are several Cerb emision friendly garages which will sort it.cant name any as it could drop them in the shite.

[dannylt]

Could be your cats which are knackered, or the engine needing a good tune up? My Cerb reached 3 years, and refitting the perfect cats which had been stored in the cellar, passed with absolute ease.

danny

[james]

Same here. Cats don't last long in a Cerbie, so it's by far the best option to store them away carefully, and only use them once a year, at MOT time

[williamball]

You have lots of choices, and indeed any combination of those below might help:

a) find a TVR friendly MOT station
b) have them check both exhausts - it only has to pass on one side; they're totally independent [presuming you're running sports pipes] so go for the best one - don't assume a fail on one is a fail on the other
c) go for a serious thrash and get it checked immediately after. The car will do better hot than if it's just tested after standing getting cold while they do the other checks
d) you could also run the RPM higher than required if the car isn't wired up to the system to detect RPM. Not strictly kosher, but quite feasible as a few systems don't have pickups big enough to detect RPM from TVR-sized spark plug leads. On this basis the system can't measure RPM so its up to the tester to get the RPM from the rev counter. Maybe it could run just a few more revs....
e) borrow a cat - see b) above - it only has to pass on one side, so put the cat on the 'best' side.
f) if all else fails, take it to a TVR dealer and get them to put it through.

WB

[Julian64]

Assuming for one moment that the cerbie (as originally designed) can pass a 'normal' MOT. So lets ignore the 'take it to a hooky MOT station', although lets call that plan B. My cerbie has standard pipes which have a common back box and therefore you can't do a check on either side.
Lots of neat fuel goes through on overrun so I can understand that cats die young on a cerb. But what changes in the lamda, CO and co2 would you expect to see if it was cat rather than engine? I'm interested in the run it at a higher rpm idea. Why do you think that would work?

[gazzab]

just stop mucking around and use an independent or a delare to get the MOT for you. They can ensure the 'set up' is correct.

[Byff]

Don't want to gloat, but -

Mine passed first time and not a dodgy tester in sight. This is despite running the car with its original cats since new. I'd given the car a bit of a thrash to get it nice and warm beforehand but it still went through the checks first, so...

I reckon you either took it for a spin round the block, tested the other exhaust or you took out the air filter.

[Jo Williams]

If anyone knows of a TVR 'friendly' MOT place in the southeast, could they please email me of list, as I had similar problems at last MOT, and want to be prepared for the next one! The dodgy hand-brake is another reason to take a Cerb to a friendly MOT centre!

TIA,

Jo

[dannylt]

I think the common back box still keeps both pipes fairly seperate, but as was said, just take to a TVR specialist/MOT station, who can tune up or diagnose cat failure as appropriate. Fernhurst did mine, appreciate not that close, but right end of the country :-)

[Julian64]

Just my opinion, but I think taking it to a dealer and telling him to 'tune' it up and MOT it is just throwing money away. I bet he does nothing to tune it up but takes it to a MOT station he has a relationship with and gets a hooky MOT at the same time as relieving you of tune up money. Incidently mine already passed but at a higher RPM than it should have. Interestingly at a flat spot the car has at 3,300rpm. Possibly an intentional flat spot for passing emissions at?
The point of this thread was not to whinge about emissions but to fully understand what happened. Cerbies have an adaptive map below 3000 rpm. Maybe its better to go into an MOT with your adaptive map cleared or reprogramed weak. Do any of you gurus have a fuller understanding?

[james]

Jo Williams said: If anyone knows of a TVR 'friendly' MOT place in the southeast, could they please email me of list, as I had similar problems at last MOT, and want to be prepared for the next one! The dodgy hand-brake is another reason to take a Cerb to a friendly MOT centre!

TIA,

Jo

The only reason you have a dodgy handbrake is because it isn't adjusted correctly. Mine would quite happily hold the car on any incline. The problem seems to be that it's a bit of a fiddly job to get it right, so if the customer is happy to accept that the handbrakes don't work on these cars, the dealer doesn't have to spend all that time getting it right when it's being serviced.

James

[dannylt]

Julian64, the dealer I was referring to *IS* an MOT test station. If there is nothing wrong with the car, it should pass fine. The fuelling is adaptive below 4k, not 3k. Clearing the map won't necessarily help, after all, the reason it's adapting is to try and get the fuelling perfect for the cats, i.e. reduce emissions. Cats like a perfect mixture.

There is no intentional flat spot at 3300rpm, plenty of cars probably have unintentional ones. You can't reprogram it weak (I don't know of anyone outside the factory who's managed to reprogram them at all), and besides, this would just raise NO emissions.

danny

[Julian64]

Confused, the more I think about this the more I realise I don't know. Why have an adaptive map at all. Why not let the processor simply calculate on the fly. Why does the ECU look at the adaptive map at all. The adaptive map by definition is always old data. If changing it simply causes the ECU to immediately overwrite? It can't be time limitation as the ECU is way fast enough to handle it. When you look at the circuit board the non volatile ram is a seperate chip. NV's are always slow compared to the processor so the processor is actually taking a 'time out' relatively speaking to read it. So there must be some mileage in being able to play with it. I'm going to take a break here and go and research this. If there's any interest I'll present back what I manage to find out.

[dannylt]

The lambda sensors have quite a delay. Therefore for driveability you want to cache the correct fuelling. The base map should be pretty accurate, the adaptive map only "trims" the main map, generally around +/- 10%, I think it considers >20% an error. Since each engine is slightly different, having this feature is required for emissions reasons.

Try the book "Engine Management" by Dave Walker (of Emerald ECU fame).

danny

[k-9]

I recently put my cerb 4.5 in for MOT, I had already bought new CATS from Blackthorn as mine were knackered. Mine still failed miserably so it took 3 days and a large amount of wedge for the garage(Main Dealer) to diagnose lamba sensors.... so really its a bit by bit process. If not Cats then its Lamba sensors in my humble opinion.