Clio sport gasket problems

[Gaz c]

Car has consistent light on dashboard saying please check fuel injections and emissions. All sensors have been changed except for the lamber sensor and the fuel injector, took it to a renault dealer who gave it a full diognestic who says there is nothing wrong with the car, since then they are now saying it could be the mas sensor which I have changed. Took it back as still under warrenty they are now saying it could be the carbon monoxide sensor which I have also replaced, this has not solved the issue as dashboard light still says the same thing. Oh by the way for these two sensors which I replaced my self in under in ten minutes and at a cost of £25.the garage wanted me to pay them at least £300 all I need is a real diagram of this engine as its obviously one of a kind. And information how to get gasket sealent off as I have undone the eight bolts connecting it and tried to remove it so I can clean the fuel injectors but it won't budge any and all help wanted and would be appreciated.