Ford Repair: Failed emissions, ford taurus, 1999 ford taurus

Question
I have a 1999 Ford Taurus SE, 3.0 engine, overhead cam, with approx. 156,000 miles. I've had all four sensors underneath replaced, and rejected, the thermostat replaced,and rejected again with all monitors still reading incomplete, after driving of course. I went to see a repair advisor and he said that the temp of the car was low around 168 degrees, and that I needed the coolant sensors replaced, I replaced them. Went back to tak the emmissions test yet again and it rejected. There is no engine light on and I am tired of throwing away my money only to be rejected, what could possibly be the problem? please help!

Answer
are you replacing these parts or are you having it actually diagnosed and repaired? if you are doing it stop it as you can see you are throwing away money and getting nowhere except broke and frustrated-if you are paying someone to diagnose it then they need to do their job and not charge anything else until it is repaired and passed. the scan tool will tell when monitors are complete and passed why are you testing it before you know this to be the case-have it diagnosed and repaired by a reputable garage it may save you money in the long run.