Went to gippsland yesterday from frankston, didnt miss a beat for the whole 340k's, even got 10.5ltrs/100k's, this morning i started it and it run fine, decided to work on it instaed of going to spend money so i turned it off, been having problems since i installed my lcd nismo cluster, it says im doing half the speed im actually doing so i thought i would put the old one back in and see if that fixed it, before i put the facia back on i took it for a quick spin, as soon as i started it i relised something was wrong, it idled like a pig and every time you reved it there was a cloud of black smoke, took it for a quick spin after stalling 3 times trying to get it out of the drive way, stalled a couple of more times whilst slowing for speed humps and still putting out black smoke.
Question is what is behind the cluster that could cause this to happen?