We took a 2011 Doosan D30S-5 in on a trade. Has a Yanmar 4TNE98 engine. Seems to run fine, but when you rev the engine, there is excessive black smoke and the engine seems to be louder than a normal Yanmar that I have heard before. Any ideas what could be the issue. One of my techs said the injector pump could off timing a little. One tech says it could be an injector. Any advice is appreciated. thanks