hi i hope some one can help me my wifes car is misfiring i have put new spark plugs and leads in and being to a garage for a engine diaanostic test they said i need to have the cylinder head off to put new vales in as the lpg fuel has burnt them out it has done 67000 miles 07 plate they said it will cost a thousand pounds to do job some one has since said that it could be the fuel injectors that need just cleaning out that would cause the engine to misfire who do i believe thanks