Cylinder Misfire

Level 2 User Joined: 26 Mar 2004 Posts: 52

Hi Guys

Took the 19 (1.4energy GTS) in for an MOT yesterday and (surprise surprise) it failed.

It failed on emissions.

The guy said that it was 6%, and needs to be under 3.5%. He said that cylinder no. 1 was mis firing therefore not burning fuel properly. (plus the mix on the carb was too high)

I have changed the plugs, leads, dizz cap and coil, but still no luck.

I can still hear it throught the exhaust.

Will a good service and general tune up sort this out, or is it a bit more drastic??

Cheers
Ben

Site Subscriber Joined: 13 Oct 2004 Posts: 4722

if its carb shud be able to change the fuel mixture setting your self

Level 6 User Joined: 20 Jun 2004 Posts: 155

If its carbed then you can easily change the fuel/air mixture and idle speed via screws located on the carb itself. If you have an Energy engine which I think you might have, then the carb is right at the back of the engine compartment, between the main engine block and the bulkhead. The idle speed screw is easy to get to - its on the front pointing upwards, on the left hand side of the carb. The mixture screw is a bit more tricky, as its round the back of the carb, so you have to get a stubby screwdriver down between the bulkhead and the screw head.

If you have a Haynes manual, it shows you where the screws are on the various carbs that were available on 19's and is probably the best place to start from. There are other posts on this subject in the forums - just search for "mixture screw" or something. If you haven't already, check the fuel filter - mine had the original one when I got it at 80k! Replacing this is easy enough and may help, otherwise a strip down and clean of the carb to make sure no jets are blocked etc seems to be the recommended course of action.

HOWEVER I would also say that I don't think misfiring isn't always down to dodgy fuel supply, especially if its only one cylinder misfiring (someone correct me if I'm wrong here). Since you have already replaced most of the obvious stuff, and assuming the replacement parts are OK, then it could be related to dodgy cylinder compression on the misfiring cylinder, which could be caused by lots of things. Again, Haynes is a good starting point for low compression diagnosis.
You could try and check the actual computer ignition module, although I would imagine it is pretty unlikely to have gone wrong unless abused in some way. If the coil was duff when you replaced it however, I suppose this may have had a knock on effect on the computer module.

I guess we will have to wait for Chris H and his panel of experts to arrive Very Happy

Cheers
Alex

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

if you have changed the plugs, leads, cap and rotor then one can assume there is no longer a spark induced missfire on cylinder number 1.

The carbed models do splutter a bit which sounds like a missfire, some do it a lot some do it every 42 seconds etc etc.

What was the HC reading? If it wasn't burning the fuel then this would have been very high, HC's are bassicalyl unburned fuel passing through.

Weaken the mixture a tad then take it for a good thrash. Also if the air filter etc is manky then get a new one it.