My Vauxhall Vectra is misfiring and a knocking sound is comming from gearbox mounting. How much do you think it will cost to repair and what do you think can be wrong with it please?
Not too much to go on here, I’m afraid, but I suspect that the knocking sound is happening because the engine is shaking due to the misfire, so it is the misfire you want to concentrate on to solve the problem.
You don’t say whether it is petrol or diesel so I’d really strongly suggest that you get a mobile mechanic to come and look at it. Regarding how much it will cost to repair, ring round and find somebody who will give you a specific price to come round and diagnose the problem area.
This could be the problem itself, but it could be that they simply rule out the fuel or ignition system and say it’s an internal engine problem, which would need further dismantling to identify. At all events, if you are concerned about the cost of the repair, ask for a quotation to do the job once they identify the problem so you can assess whether it is worth having the work done at all.