Exhaust Problem?

It sounds as though one cylinder is not firing, or possibly has low compression and/or a slightly burnt valve, so one cylinder fails at low speed, giving the puffing sound and picks up when running a bit faster so there is no major power loss.

To diagnose it I would either disconnect each injector (if you can) and check the speed drop/recovery sounds the same on each cylinder, or expose the ends of the ht leads and short each one to earth , again compare the sound and engine speeds. When you have established which one is the problem you can investigate better. First checks would be an air leak, maybe at the inlet gasket or vacuum pipe connection, then move on to plug, coil/spark, then compression then valve sealing.

mrcheerful

since you've had a misfire the cat could have melted causing a blockage, ive seen it a couple of times, it melts the monolyth from the unburnt fuel, the exhaust is trying to force out whats left of the cat creating a blockage in the exhaust, prolly worth un-bolting the cat and looking down it.

Thanks for the reply. I forgot to mention that we have been through the leads check and even had a compression test and i was told that the compression was very good, so sticking valves was ruled out.

Thanks for replying. Does this mean the catalytic convertor needs replacing then? sound expensive, if the cat is taken off what should I be looking for when i look down it?

if its melted or broken up then a replacement is required, prolly circa £130 shop about you might get it cheaper, if the monolyth is in one piece you should see a honey come effect similiar to the one here

So have you checked the cylinder balance or not?

Sorry not really sure what that is, tonight the car now has another problem on top of this. Off side front indicator, side repeater light, and tail indicator lamp all staying lit.