Expert: Mike Evans - 12/30/2009

Question
I have a 1993 chevy lumina with a v6 and 3.1 fuel injected engine.
it is making a horrible noise under the hood.... it looses power and has a small oil leak.  could you please tell me what it is .... It started dec 26th coming up the interstate and lost the power climbing a mountain.  I first thought it was a rod about to shoot through the motor. then i decided it would have already done that.  some people have told me to check the bolts on the torque converter, spark plugs, and flywheel, haven't checked all of that yet. just wanted to get your opinion.  it sounds like thou, thou, thou, thou. fast sounding.  

Answer
    Diagnosing an engine noise without hearing it is almost impossible.  That said, I am thinking the most likely culprit, since you report a loss of power, is a valve problem.  It could be a bent pushrod, a failed rocker arm pivot, or even a burned exhaust valve.  Another possibility is a clogged or collapsed catalytic converter.  It would rob power and cause all sorts of problems airflow through the heads, which could cause a variety of noises.  Another less likely problem is that a spark plug may have blown out.  It happens sometimes, and makes a chuffing noise accompanied by the loss of power.  I think you need to let someone listen to the engine up close and personal, they should be able to solve the problem in short order.