80, 'N' reg - acceleration and smoke problems

[fenboyandy]

[quote=jonathan_dyane;157936]

Incidentally, the car does not need the cat to pass the MOT, so if it was to need replacing due to blockage I personally would cut it out and replace it with a straight piece of pipe. This has the added benefit of making the car slightly more responsive, and improving the MPG...

Good luck,
Jonathan.

Hi,

Found this really interesting - is that 100% right? I've got a '94 L-reg and would like to ditch the cat, but assumed the car wouldn't pass MoT without one.... Is it due to the age of the car that it WILL pass MoT without a cat? Does lack of cat not mess up the emissions??

Cheers

Andy

[jonathan_dyane]

Found this really interesting - is that 100% right? I've got a '94 L-reg and would like to ditch the cat, but assumed the car wouldn't pass MoT without one.... Is it due to the age of the car that it WILL pass MoT without a cat? Does lack of cat not mess up the emissions??

All the diesel smoke test used for MOT does is test the opacity (density) of the smoke emitted by the vehicle. Diesel catalysts of this generation allowed manufacturers to meet EU emisision standards for *new* vehicles, although VAG prempted this legislation, bringing the cats in in the early 90's.

A TDI powered car will easily pass the MOT smoke test *without* a cat provided it is not smoking excessively due to being in poor condition or badly setup, indeed my father runs a 80TDI which has had the cat removed, and it passes the test by a large margin.

However, I have known over-zealous testers to fail diesel cars when they have realised that a cat has been removed, despite the emissions being within acceptable levels. This is IMHO a dubious interpretation of the MOT regulations. I have heard of people avoiding this by removing the cat and setting to it's innards with a masonary drill which causes the brittle subdstance within to break down and be easily tapped out. This leaves the tester unaware that the cat is empty as the external apperance is as normal. The position of the 80 cat may make this difficult to acheive however, due to the length of the pipes which are attatched to it...

The bottom line is that very few diesel vehicles had cats in the early 90s, and the tester is unlikely to spot the fact that it is not present, and the car *will* pass the smoke test, provided it does not have any faults (which would probably cause the car to fail *with* cat too) and you will gain an MOT with no problems on this score...

Hope this helps,
Jonathan.

[fenboyandy]

That's really helpful, thanks a lot Jonathan!

My local MoT guys are generally pretty sound, so I'd be confident they wouldn't be too up-tight about it ;-)

[jonathan_dyane]

That's cool; you can now look forward to more power and economy!

While you're on, why not make up a blanking plate to disable the EGR ;-)

Jonathan.

[fenboyandy]

ahhh.... tell me more!!

[jonathan_dyane]

Ok, well the EGR is a device which is designed to reduce the production of NOx, (Nitrous Oxide) which is one of the factors in smog. This is acheived by a valve, which under what the computer judges to be suitable conditions (part load) admits exhaust gases back into the clean intake, to be reburnt for a more complete combustion.

This works reasonably when the car is new, but as you would imagine forcing the engine to breath its own sooty mess has unpleasent side effects, namely the clogging of the inlet manifold with solid deposits. This results in the car smoking excessively!

Unfortunately, unlike on some other vehicles, the EGR cannot be disabled by either unplugging the electrical connector from the valve or by intefering with the vaccum piping, as the computer will realise this and reward you with the flashing diagnostic light...

The way to go is to remove the EGR valve (located to the drivers side of the car on the inlet manifold, with pipe running to the exhaust manifold) from the manifold and replace the gasket with a solid piece of metal shaped to fit in it's place. Result: no EGR and a noticeable increase in power and economy.

I would suggest it would be wise however to remove the inlet manifold entirely, to permit you to remove the deposits which it will contain from when the EGR was active. It is common to find the passages reduced to less than 1/2 capacity!

Cheers,
Jonathan.

[fenboyandy]

You're a mine of genius info Jonathan - thank you!

[jonathan_dyane]

You're a mine of genius info Jonathan - thank you!

Always a pleasure!

Jonathan.

[moaning]

Just reading through some of these posts, and very heartened by the mileages these cars can clock up. I love my 80 TDI, but the economy just won't get better than 40 mpg. It starts on the button, pulls very well but does smoke a bit, especially when pulling away. the car seems very smelly compared to our 4 year old Fabia TDI. As its only done 119K what's the best thing to investigate first? Diesel Bob said they would overhaul the injectors and reset the pump timing. I thought the pump timing couldn't be adjusted, and can't think that there's much wrong with the injectors. Is it not more likely to be just coked up on the inlet side from the EGR system? If so can this be sorted without dismantling? I've run a couple of tankfuls of fuel treatment through replaced on the bleed off pipes, changed the thermostat and air filter.

Is it a good idea to remove the EGR pipe to inlet manifold and squish some kind of decoke spray in?

[xylophone]

Hi,

I'm the originator of this thread. My 1995 80 TDi Avant. Had to replace turbo recently. Volksparts, excellent outfit in Durham, did the job. £700. First 'big' part have had to replace. Now on 235,000. Still on original gearbox, clutch, exhaust, engine.

Time, I think, to replace car with an A6 Avant, say 2-4 years old, for greater comfort, capacity. Second hand prices at all-time low. Any comments, anyone, on this car?