buying an emission tester.....

the gunsons will be fine as a near enough guide for old (pre cat)petrol vehicles (I have one of the 'pro' versions and with care it gives pretty close results) it will be useless for anything current. diesels use a visual tester which measures smoke, so needs a different system entirely. A setup to do everything will be about 5000 pounds upwards and will need regular servicing.

Leave the modern stuff to mot test stations, by all means set up your mini, but don't be too surprised if your results differ from a professional machine.

mrcheerful

It'll do your Mini close enough, but it won't be accurate enough for EFI cars with a cat. It won't do diesels either; I don't know of a DIY machine that will.

just to give you an idea our petrol / diesel emission analyser cost us approx £5000 for our test station.

=A35000!!. my budget was more or less =A350. so i guess i will stick to checking my mini.

also this gunson model checks CO. I heard there are also multi gas analysers that check stuff like HC and NO (I am not too familiar with these gases).

For general health check of my mini would i need a tester with HC capacity or can i get an idea of HC state of heath by looking at the CO reading?

thanks

also this gunson model checks CO. I heard there are also multi gas analysers that check stuff like HC and NO (I am not too familiar with these gases).

For general health check of my mini would i need a tester with HC capacity or can i get an idea of HC state of heath by looking at the CO reading?

thanks

HC readings would be helpful, HC's or hydrocarbons is the reading for the unburnt fuel that's being emitted into the atmosphere, 1200 ppm ( parts per million) for a non cat vehicle. average reading is around the 300-600 ppm, unless its got a misfire then the HC's shoot up through the roof. as of yet we don't check the NOx (oxides of Nitrogen) , but have the facility to do so.

It'll set up idle CO for you, but not much else than that. It won't measure overall emissions to MOT standards. It's easier to use than a Colourtune plug, but nothing like as versatile either.

Either save your money, or look around for S/H. If you keep your eyes open then there are a lot of S/H garage kit that's no longer up to the contemporary MOT standards and so is sold on for peanuts.

forgot to add that the 1200 ppm is the maxium reading allowable for a non cat test. ive had cars with higher readings in which case the procedure is to rev the vehicle at approx 2000 rpm for 20 seconds if the HC's drop below

that explains how old carburetted Ferraris get through the test !! from the factory they had a job to be under 1200

Mrcheerful

How about a Gunson's colortune instead? I've never tried one, but it seems a clever idea.

Basically it's a transparent spark plug.

how do you use it to see engine is sane in the CO and HC department?

Depends why you're measuring CO and HC.

Sometimes people use those measurements as a guide to setting the mixture. The colortune seems a more direct measurement of whether your mixture's right-- never mind what the book says, you can see whether it's burning with the right coloured flame. And I would think if the flame colour is about right then the CO and HC should be sane.

If you want to know actual CO and HC levels, the gas tester might be better.

you can view the flame font, colour shape size ect through the clear "spark plug", which will the give you an idea how efficiently the fuel is burning.

a few on ebay for a few £'s if you wanted to have a go.

If it's an old Mini with a carb or carbs, there's really no point. If the engine goes off tune it will be obvious by poorer performance - idling, etc. You can check mixture strength as accurately as a Gunson meter by simply lifting the carb piston about 1/8th".

I've got one too and can never get meaningful results out of it on the SD1. A garage tester gives an immediate sensible reading, though.

there are a couple of tricks to use: run the tester off a separate battery (preferably with a charger) and let it warm for 15 minutes, then set the free air setting of 2, warm the car by driving and don't let it sit idling for ages before checking the exhaust, if it idles for more than a couple of minutes you should 'clean it out' by running on a light throttle at about 3000 rpm for at least thirty seconds. You should then get a sensible, close to accurate reading.

Mrcheerful

What's the theory behind that? Is it rubbish on the supply from a car battery?

Done all that. Still gives a reading nothing like a garage one. Funnily, if I use it on my BMW with cat it gives something more sensible.

Main reason is so that the machine can be hot when you get back from your warmup drive !!!

Second of course is that the battery voltage on the car may vary a bit (especially if the fan kicks in) and this can vary the reading.

The other trick is to handle the unit very-very gently as even a slight knock means that it needs to be recalibrated. (this is even more important when the unit is hot, I don't know why, but I assume there is a hot wire or something inside)

Mrcheerful

..and mixture at idle will have not much to do with mixture/timing while driving.

If you're doign it for interest and the money isn't needed then maybe get one and have a play. I did see them on special at Halfords a while back and I was tempted but all my cars have relatively modern computer controlled engines now.

Which a Gunson emission tester won't help with either. It can only be used at idle.

Indeed.