Reducing emissions before MOT

[rawthey]

1990 740, non-turbo 2.4 l. 190,000+, about 2000 miles per year. Cat re-fitted three years ago.

Just coming up to MOT time. I remember last year the garage remarking that they had difficulty in getting the emissions low enough...(I think that they adjusted the timing and added some fuel additive to clean injectors??) I can't immediately find a guide on this forum of what I can do in advance to help. New distributor cap? (never been changed), plugs/cables? High revs for a while? (usually I keep them below 3500). Some type of fuel additive? new cat? new lamda sond? (but that is only about a year old). Any other pointers.

Many thanks.

[rawthey]

Just found this thread: "Failed emissions on MOT. Car is running lean." which has provided me with some other pointers.

Thanks for reading

[Dirty Rooster]

Being a 1990 car your emissions targets are quite low compared to modern stuff and things with a CAT.
Are you sure it nearly failed last time?

[StanC]

I usually use one of the 97RON fuels - Shell V-Max, BP Ultimate, etc - not for the economy, but for the cleaning effect they have. My MoT emissions test results are always excellent and I'm sure using these cleaner fuels plays a part. Sticking in a tankful of one of these fuels a week before the MoT and giving the car a blast might help.

Stan.

[Dirty Rooster]

Yeah I'd go for the Shell one and use that alone for at least a month.

[rogerthechorister]

Spend a week caning her to 5,500 rpm, and maybe take the air filter out.

[NewVolvo]

Super unleaded fuel, a bit of spirited driving and a long motorway run will help. Some fuel additive will probably help too.

[StanC]

Originally Posted by rogerthechorister

Spend a week caning her to 5,500 rpm, and maybe take the air filter out.

Good point, Roger. If the air filter is at all blocked, that will tend to put up the emissions. Also, if the engine oil and filter is due for a change, getting that done will improve the crankcase gasses which will, in turn, improve the emissions.

I'm not familiar with this engine, but if it's got a crankcase breather flame trap then it's worth stripping that out to make sure that the whole flame trap/breather system is clean and clear, to ensure that the crankcase gasses are at their best.

So, changing the engine oil and filter, and the air filter, and cleaning the flame trap/breather system before the MoT will all help with the exhaust emissions.

Stan.

[TonyS9]

There was a fuel system / engine combustion clean out machine and fluid that was used on Wheeler Dealers recently they used to give the engine a really good clean internally. Dramatically reduced the emissions on a BMW, cost about £70.

[rawthey]

Originally Posted by Dirty Rooster

Being a 1990 car your emissions targets are quite low compared to modern stuff and things with a CAT.
Are you sure it nearly failed last time?

Thanks to all for advice: fuelled up and being driven harder!

I'm trying to sort out the emission test requirements:

(1) As it is first registered 03/1990, is your view then that it only has to meet the standard emissions test?

(2) When I first bought the car (2007) it didn't have a cat. However, a few years ago, when the exhaust was replaced, my local garage re-instated a cat "because it was in the original spec".
(2a): Were the garage correct to do this and (2b): does this mean the car now needs to meet the basic emissions test?

(3) If the answer to (2b) is yes, and the car won't meet the spec, can I then remove the cat and have it retested to the standard test requirements?

(4) have I missed anything - and is it your view that your answers are clear cut!

Thanks again.