Hello, I'm sorry nobody has answered sooner, I hope I can offer you some assistance.
Is the engine a petrol or diesel? Does the engine make any unusual noises?
Let me know and I'll reply as soon as I'm able to.
the first thing to check on this engine is to make sure the injector seals aren't leaking allowing compression from the engine to blow past. The injector is sealed against engine compression by a copper washer at the base of the injector, when this washer starts to fail hot gasses blow past, the smell is caused by the hot gasses melting the plastic bush that sits around the injector to aid centralization when fitting the injector.
If this is the case you can usually see molten black plastic around the injector where it fits into the cylinder head.
To cure this concern requires injector removal and the injector copper washer replacing, the seat where the injector sits also requires cleaning, this needs to be done with care to avoid any debris entering the cylinder, there is a special tool to prevent this happening if you are wanting to do this on a DIY basis.
Other than this common concern check there are no fuel leaks from the injector return pipes where they connect to the injectors.
Start with these points, let me know if I can assist further and I'll reply as soon as I'm able to.