Both of your observations are wide open to interpretation. You have to describe the knocking, and "won't go as fast". My 25-year-old Grand Caravan doesn't go as fast as when it was new because it has well over 410,000 miles on it. Do you mean it takes a few seconds longer to get to 60 mph, or it struggles to get to 30 mph?
Do you have an oil pressure gauge on the dash? If not, having the pressure checked with a mechanical gauge is the first step. If it is real low, suspect worn engine bearings. The resulting knocking will be plenty loud to hear a long way off. That will also be detected by the knock sensor, and as a result, the Engine Computer will retard ignition timing in an unsuccessful attempt at stopping the knocking. That reduces engine power noticeably.
Did you determine why the engine didn't start? If it was spark-related, raw fuel would have run into the cylinders, past the rings and into the oil. Oil diluted with gas will destroy the engine bearings very quickly, as in less than a hundred miles.
Some other causes of knocking can be much less serious, but still, if the knock sensor detects it, engine power will be reduced.
Monday, February 2nd, 2015 AT 6:58 PM