Meths in fuel for MOT?

[david151]

Today I had the car fail on the MOT for emissions. The MOT refusal sheet says:

(10.95%) Exhaust emissions carbon monoxide content after 2nd fast idle excessive
(981) Exhuast emissions hydrocarbon content after 2nd fast idle excessive
(0.70) Exhaust emissions Lambda reading after 2nd fast idle outside specified limits
(I think I know what is causing the Lambda reading as it also failed on a hole in the exhaust which I read can cause a high reading for this)

First of all does anyone know if these figures are borderline failure or are they miles out?

Secondly I have been reading a few posts about people mixing meths in with the petrol for the MOT. If I do this should I just use meths on its own or would it also be advisable to also bung a bottle of Wynn's Clean Burn as well? I used the clean burn stuff about 1 month ago when I changed all the filters etc, however it obviously has not cleaned everything.

For the retest I plan to rev the crap out of it before I take it in, however I just need some advice regarding the meths and the things it failed on.

Thanks Dave

[Mr2Mike]

You haven't said what the car is, so it's difficult to comment. If it's a modern car then those numbers are absolutely miles out.

For a car first used between 1995 and 2002

Natural idle
CO 0.5%

Fast idle
CO 0.3%
HHC 200ppm
Lambda 0.97 to 1.03


For a car first used from 2002 on

Natural idle
CO 0.3%

Fast idle
CO 0.2%
HHC 200ppm
Lambda 0.97 to 1.03

Adding meths to the fuel isn't going to fix emissions that are that bad, you need to diagnose and fix the fault that causing this.

[david151]

The car is a Mazda 323 1998. It's the girlfriends car that she has been using for the last 3 months. I think part of the problem may be that the distributor is bad. At very fast revs it just misfires, which is obviously contributing to the poor readings. A local mechanic even confirmed this.

The problem is the car only cost £150 so it is really not worth spending money on parts. Anything that can't be sorted by myself for a very cheap cost is not worth it. That's why I was wondering about any tricks such as meths etc. The annoying thing is that is all the car has failed on. I think I will have a go at welding the exhaust and then just sticking a litre of meths in an almost empty tank and ragging it like crazy before taking it in for test - what do you think?

[Mr2Mike]

If it's misfiring that will probably be the primary cause of the poor emissions. It won't cost a lot a lot to fix it properly, and you'll likely recoup the savings in fuel pretty quickly.

[david151]

As I said it only misfires when you floor the accelerator at really high revs. The problem is they seem to do this on the emissions test. It is definitely a faulty distributor (had this confirmed) so it is not so cheap. today I made a stop to prevent the accelerator cable from going all the way, meaning they can't physically make it misfire as the cable will only partially pull the throttle. Any ideas how the MOT tester will view this?

Any ideas what the regs say about doing this type of thing?

[Evoluzione]

david151 said:

As I said it only misfires when you floor the accelerator at really high revs. The problem is they seem to do this on the emissions test. It is definitely a faulty distributor (had this confirmed) so it is not so cheap. today I made a stop to prevent the accelerator cable from going all the way, meaning they can't physically make it misfire as the cable will only partially pull the throttle. Any ideas how the MOT tester will view this?

Any ideas what the regs say about doing this type of thing?

A cunning plan! I like the way you think, I can't see it being in breach of any rules as long as they don't notice.
I'm with the others though, just fix it, surely some used parts can't be so expensive. Sometimes you've just got to bite the bullet, I'm currently running the GFs Fiat Coupe 16vt (which we picked up for £400) on used and cheap bits, probably spent twice it's value on running costs, but still a years reasonably quick and stylish motoring for less than a grand isn't too bad.

Take a read here: http://web.anl.gov/PCS/acsfuel/preprint%20archive/...
About what adding Methanol did to vehicle emissions, I did ponder on buying some and running a car on a percentage of it, not sure yet though...

[Mr2Mike]

david151 said:

As I said it only misfires when you floor the accelerator at really high revs. The problem is they seem to do this on the emissions test.

The high idle speed test is only actually performed at between 2500 and 3000 RPM. If they are revving it harder at some point then perhaps they are simply trying to heat up the cat to lower the emissions.

The CO emissions suggest that the engine is running very rich, it must be guzzling fuel driving it in this condition and if it's been like this for long chances are the cat is now well past it's best.

Have you checked to see if any diagnostic codes are stored? This could be as simple as a knackered coolant temperature sensor.

Edited by Mr2Mike on Wednesday 31st October 22:22

[D_G]

Your figures are miles out. 1000 HCs and 10% CO is very rich, the lambda reading is as low as it'll go too. It's worth getting a diagnostic check done as it could be something minor, split pipe after MAF, lambda sensor, coolant sensor. Only real way to tell what's up, it won't be fixed by an 'Italian tuneup' though I'm afraid.

[Willhook]

Find a 'friendly' MOT station and get them to use a donor car for a reading? I have heard this done a lot with de-cat vehicles.

[Andy 308GTB]

Willhook said:

Find a 'friendly' MOT station and get them to use a donor car for a reading? I have heard this done a lot with de-cat vehicles.

This is probably how the car had an MOT Certificate in the first place - I would take it back to the same garage.