Supercharger And Effect On Emissions
 

Hi from the UK.
I took my car for a MOT today and it failed on Emissions.

It does this every year and then I use a cleaner like Cataclean and take it for a long run and it normally passes.

Just a thought and I hope someone can tell me the answer.
If I disconnect the Supercharger (as in remove the belt) what effect would it have on my emissions test?

When my pulley sheared many years ago I had to use my car and it just became like a standard MX-5 (Miata).
That's why I'm thinking what would happen to my emissions if I just took my supercharger belt off?

Could this be the answer to passing the MOT emission test?

Full Disclosure - I'm replying from Canada.

I looked up the emissions testing for UK - this is what they do for vehicles newer than 1 August 1992
The first test consists of checking the emissions at ’fast-idle speed’ which involves running the engine at a speed of 2500 - 3000 rpm. During this test the emissions of CO and HC will be checked and a further check will be made on the lambda (1) value. The second test consists of a check of emissions at ‘normal idle speed’ in which the engine will idle between 450 and 1500rpm, but in this case only the CO emissions are assessed.

Before that date
For vehicles first used on or after 1 August 1975, emissions will also be checked using an approved analyser. After completing the visual test, the tester will use the analyser to assess the concentration of carbon monoxide (CO) and hydrocarbons (HC) in the exhaust gases by inserting a sample probe into the exhaust tailpipe. The test is carried out with the engine at its normal idling speed and the analyser displays the results continuously. Once a stabilised figure is achieved the tester will record the result.

Are you running a factory ECU or some kind of aftermarket? Different injectors? Boost sensing piggy-back(s)? Other engine modifications? All of these will factor into your emissions.

The quick answer is: If you run a factory ECU with boost sensing piggyback(s) and no other modifications, then removing the belt and tying the by-pass valve open will give you (as near as makes no difference) a factory setup.

I miss the old days when you could adjust the mixture by turning a screw.

Here's a link to my car info:

Supercharged MX5 Jasper Conran Special Edition "The Beast"

I have Greddy E-Management.

It failed on:
Fast Idle Test
CO result 0.60% (limit 0.3%)
Lambada result 1.037 (limits 0.970 - 1.030)

I have a new O2 sensor on the way.

They did the test twice the first results were:
CO result 0.65% (limit 0.3%)
Lambada result 1.051 (limits 0.970 - 1.030)

So readings did drop on the second test.

Just to add it was really cold here last night and I took the car in without taking it for a blast first.
I had trouble getting into my car as the doors had frozen solid.

Ahh, the veritable BRP MP62. Looks just like mine used to....sniff.

That new O2 sensor should fix you right up.

If you still want to pull the belt (I doubt you'll need to) Do you have factory injectors? If so, e-manage is a piggy back. Disconnect and plug the vacuum hose, remove the belt, tie open the bypass valve.

Fitting the sensor is not going to be easy with the charger in the way.

I think I have the original injectors.
I have no recollection of any paperwork saying otherwise.

When you say "disconnect and plug the vacuum hose" which hose are you referring to?

The hose part shouldn't be necessary. Disconnecting the drive belt will keep the emanage from seeing boost and accomplish the same thing.

Agreed, unless it is tuned to start below zero. It's a simple enough thing to disconnect the hose and be sure.

Little Badger, there will be a vacuum hose leading to the e-manage. Remove it from either the engine or the e-manage. Cap or plug the end going to the engine (so there is no vacuum leak).

I don't want to leave this thread hanging for future searches.

I replaced the O2 sensor and took it back for the MOT retest.
It failed again.

I decided to replace the CAT.
When the mechanic took off the old CAT we found out it had been De-Catted.
Checked the emissions after we fitted the new CAT and it failed miserably with a CO% level of over 4.

Came to light that my new O2 sensor had failed and was not changing the output voltage.
Fitted a replacement O2 sensor and it passed the MOT.

But now I have another failed O2 sensor but I want to start another thread on this matter.

I just realized you have a 2000. NB1s have the notoriously faulty coil packs. Have you changed that? The excess fuel will continue to kill everything downstream, O2 sensors and cats.

I had a faulty coil pack when I first bought the car 10 years ago.

Took awhile to work out what was wrong with my car but I bought a brand new Mazda coil pack and fitted it.
All problems disappeared.

The O2 sensor in the car took all the beating and went on for another 10 years before I changed it.

When I was having problems with the rich CO reading I bought a used coil pack and OHM tested it before fitting it.
The problem was still there so I switched back to my original coil pack.

I've just ordered a working used Mazda O2 sensor. I'll fit that and see how it goes.
If OK I'll save up for a new Mazda part as they aren't cheap over here.

Where are you in the Uk? PM me or find me on MX5Nutz - same name

I'm in Bristol

OK here's an update.

I received my used o2 sensor and started removing the current one.
It then came to light that the used one I bought was too short.
Sent it back to seller and he sent me a longer one.

But here's the odd one. After I reconnected the one in my car the hesitation problem has seemed to have disappeared.
I've been driving it from Monday and all seems fine.

It may have been just a loose connector.
I'll keep driving and report back.