Hi everyone, I've tried to figure this out with no joy.

On hard acceleration I'm getting lots of black smoke and I also get some engine stuttering even at speeds of 50moh and above (including in cruise control)

I have replaced the fuel filter, the air filter, treated the fuel with suppluments but no change.

The car starts first time every time.

Any ideas? It's a 2005 2.0 with 110k on the clock.

 

Read the codes. Sounds like an O2 (upstream) or MAP/MAF (forget which in this car) sensor, or injector problem.

 

sounds like you are running rich or have a cool spark. How do the plugs look (my guess is one or more is sooty black)? when were they last replaced? Anything odd going on with the temperature gauge? Did you scan for any stored CEL codes? As habby noted there's several sensors which come into play for fuel trim - O2 sensor, MAF (airflow sensor), ECT (engine temp sensor) MAP (manifold air pressure - some engines have two). Any signs of oil consumption (ie PCV oil separator allowing oil into the intake)?

I'd probably start by doing an OBD scan, inspect/clean/replace the plugs (go OEM for best results), open the intake to check for oil or dirt (possibly due to a failed oil separator) and inspect/clean the MAF (use MAF cleaner not carb cleaner), check the wire harness to the coils for cracks in the connectors. If your OBD reader has a real time data feature, monitor run time data to see if it gives any insights into fuel trim, O2 sensor signal levels etc..