Ok people here goes...I have an 89 740 16 valve...98k on it...I am having a bad problem with black smoke and poor fuel economy. The guys at the dealership checked it for everything so they said...I have replaced the ICM, ECM, AMM, checked for vaccum leaks, they cleaned the throttle body I think, andmade all the correct adjustments to the fuel system. The check engine light is NOT on, the car runs great, idles smoothly and doesn't miss. I just hate to get 8 MPG and have black smoke pouring out of the thing all of the time. Help please...[sm=boohoo.gif]

 

I had the same problem with my 8 valve engine and it turned out to be a leaking fuel pressure regulator. I'm not familiar with the 16 valve engines but you should still have one of those. I would check the fuel pressure regulator and the O2 sensor if everything else has been replaced. Have you tried to check the codes yourself? You should have one referring to "lean out of limit". My check engine light didn't come onwhen I had my rich running problem too.

Dale

 

Someone missed something at the Dealership when they looked at it.

Black smoke means running way to rich.

 

new injectors?