I think that four days is pushing the limit - this will not improve the flavour but rather tend to break down the fibre of the meat so as to render it a congealed mass with no texture or body - might as well be eating a pudding . Any marinade that contains acid, alcohol or salt should not be used for very long, because it will chemically "cook" or denature the food in it. Marinate food in these marinades for less than 4 hours. Marinades that contain citrus juices, especially lemon or lime juice, should be used for only two hours or less. Marinades that contain no salt, acid or alcohol can be marinated overnight or, in some cases, longer.
Although marinades thwart bacterial growth and help extend food's life, remember that the food in them is still raw and must be treated as such.