I just changed the engine on my 97 Taurus and now I'm getting two Oxygen
Sensor trouble codes, P0136 and P0155.  One is for the pre-catalytic
converter on one bank and one is for the post-catalytic converter on the
other bank.  Before I put the new engine in, all the Oxygen Sensors were fine
and working.  I'm skeptical because what are the odds that both would go
simultaneously.  I'm thinking that maybe something isn't right with the
electrical harness that came with the new engine in which all the sensors
plug into.  If anyone could let me know what is likely to be the problem I'd
be most grateful because something tells me that if I spend $150 on two new
sensors that the problem won't just go away.