Land Rover Repair: Failing Smog Test, vacuum leaks, smog test

Question
See what happened was I took my 1999 Disco II in for a smog test. The check engine light had been on, so the tech. plugged it in for a diagnostic test. The test brought up ( 3 ) codes. Two of the codes pointing to the front 02 sensors and the third as an undisclosed code. He suggested I have both O2 sensors replaced and then the third code should then go away. I had the mechanic replace both of them and then the check engine light still popped back on. So now he figures that the seals or o-rings (as he calls them) where the air intake is for the engine, need to be replaced. He says that there is probably more air mixture to fuel which is what is causing the O2 sensors react and send the check engine light to appear. Does this sound right? Or can you shed some light on what are some common problems for smog test failures?

Answer
Hi George,

it's very rare for O2 sensors to fail.  Clearly, they are part swapping to solve this problem.

How are your spark plugs, coilpack and wires?  This can have a huge impact on emissions testing.  If you have high mileage I can understand these troubles.  Check the old spark plugs...they can reveal how your engine is running.

Make sure the burn is good, no vacuum leaks anywhere, timing is set properly.  

Best of luck,

JohnMc