To be honest, I haven't checked the compression on the cylinders. The car had been a bit sluggish but I put that down to the colder weather, once warmed up she was normally fine. We took her out for a drive and the engine light went on and she skipped into limp home mode, I got her to a lay by but by that time the smoke was there and then the hissing from the engine bay. There does not appear to be any leaks from the engine of oil or water so I am really not sure. We live in the North of Scotland so before I get her towed to a garage I wanted an idea of what I am up against.
a hiss would usually be an air leak or failed valve. the covers need to be removed to verify the source.
black smoke from the exhaust would normally be due to an over fueling issue which could be due to a bad airflow or temp sensor or injector or fuel pressure issue.
black smoke from under the bonnet again indicates a leak of some kind, which would need to be again verified visually or with a pressure test or smoke test.
since the engine light is on, the other important step is to have the fault memory read out from the car's computer.
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Thanks, XXXXX XXXXX the answer and I know it can be hard when you cannot see the vehicle or the symptoms. I will give you a good rating, at least I have a little information to discuss with the garage so it looks like I know what I am talking about!!