Help required with MOT failure on emissions

[embee]

..... emissions...... were "all over the place!"

Ermm, that doesn't really narrow it down very much. Go on, give us a clue ..................

[bus_ter]

A common theme with these posts is having the CAT stolen and a cheap third party replacement installed. Could it simply be that cheap CATs don't last very long, maybe start breaking down internally and stop working effectively?

[Andyroo]

Sorry, I ought to have clarified:

Unburnt hydrocarbons should have been below 200 ppm but were in the low thousands. Since posting this yesterday I took the car for an "enthusiastic" run along the A1 and can confirm the following:
1/ This car moves like a scalded cat when pushed! I LLOOVVEE driving it!
2/ At the commencement of the trip M.P.G. was at 43.1 and by the end of this high-speed run was 43.2, so in spite of being belted it's still pretty economic on petrol.
3/ Before the above my wife had noticed an occasional "engine management" symbol flash; examination produced a PO304 error, cylinder 4 misfire. I cleared the code and it DIDN't reappear during the 40 mile belt through the Hertfordshire countryside.
4/ I'm going to buy some injection cleaner tomorrow and use as per instructions.
5/ Would cleaning the E.G.R. valve help? I'm perfectly capable of so doing, but don't want to do so unnecessarily.

[springswood]

I'd been told Honda engines are happy to rev, it does make the humble Jazz quite fun.

Is it possible that the misfire code is from before you replaced the plugs and coils? If not did you check the gaps? I confess I don't always as I can't remember when I last had one that wasn't right. Otherwise perhaps try swapping the cylinder to identify a faulty part. Though with an intermittent code it could take a while. Doesn't seem very worrying to me.

Cleaning the egr valve is so easy I'd try it myself. It may be heresy but I've found the gasket can be reused.

[MartinJG]

When I was young I always drove old bangers. A fast and long drive would give them a tune-up, (decoke) Another noticeable thing was an improvement in performance when it was raining.

Two stroke motorbikes used to run much better in cooler damp conditions.

When the 500cc GP bikes such as the Honda of Mick Doohan were north of 170bhp,  the Honda 2-stroke had a water injection system,  the Harrier VTOL has a water injection system for the Pegasus jet engine, my Metro 998cc of 1982, the engine seemed to run better when driving through the country roads when there was plenty of mist trapped by the trees. I believe the mist is turned into steam during combustion in the cylinder,  steam can be a very quiet as driving force comparing steam traction engines with vintage industrial engines at country fairs

I think what happens is that the 'steam' factor helps to break up the fuel vapour for a more efficient burn. I have noticed this is more pronounced with diesels where greater compression comes into play.

[KJazz]

Mavbill, always always always keep your mot requirements. That is a history of your car at your finger tips.