Misfire and smoke coming out of catalytic converter

Hi
id be grateful for any help 
i have a 2006 Jimny which has been off the road for a couple of years 
i swapped the old engine for a M15a from a swift and have been fixing the rust
i took it out for its first run today
ran fine for a few minutes and then started to misfire badly
managed to get home and found smoke billowing out of the catalytic converter under the car
any ideas what is going on??

thanks 
Tom

Have you got a OBD2 code reader?

Misfire can be a number of things, coils, weak battery, wrong mixture, a sensor or a combination of things.

Smoke shouldn't escape from the CAT, so that suggests the CAT has a hole in it. If that is the case your O2 sensor in the exhaust might be giving strange readings and could cause a misfire.

What colour is the smoke?

Robin

thanks for your reply
no check engine light and can't get any codes on my OBD reader
the smoke is grey and smelly and I'm wondering if I could have dropped oil/ plusgas etc on to it when I did the engine swap and that is burning off now??
I had a feel around the union at the front and back of the cat when it was cold and no obvious leaks of exhaust gases with the engine at tickover.

Hi,

If you have a leak in the CAT, you would certainly hear it and maybe see jets of smoke coming out. I doubt supose you really want to stick your hand underneath but you might feel the leak. The CATs run very hot so will burn anything that is on the outside.

Grey is not a natural colour for something major in the engine and depending on what it smells like, it might very well be just burning something off the outside, either oil from the engine swap or if it has been stood for some time it might be an accumulation of general grim.

If the smoke coming out the back looks ok, it isn't over-heating and the water is not getting pressurised then it is starting to sound more likely it was on the outside. If that was the case, it will burn it off soon.

None of this tackles the misfire, but again if it has stood for a while you might have water or something else in the fuel or one of a number of other issues.

Robin

Do you live in the countryside, not unknown for critters to build their nests in exhaust pipes, if they have built up a nest then it might be choking the engine up. Have you tried to start it since, once the pressure subsides it should be okey for a little while