Car runs fine with decent mileage but blackens the exhaust pipes after only a few miles.

 No smoke, no CEL -- why the black pipes so quickly? 

Gas is from my regular station and runs fine in my other cars.

'94 LT1 Auto with only Corsa exhaust.

Any input would be appreciated.

C.

Now it's running rough and my mileage is down.

Starts ok, just runs rough like it's misfiring. Blackens up the pipes quickly too.

Not sure if it's Optispark, wires, or plugs so I'm guessing that's a good place to start.

24k miles and has had best of care from original owner.

Any help would be appreciated.

C.

I understand that this might be as simple as a temp sensor -- which one might that be and how to test it?

C.

Thanks Joel -- Is this the suggested procedure?:

 http://www.corvettebuyers.com/c4vettes/codes.htm

Thanks 396...no scan tool for my '94 system AFAIK -- have to read the ECM another way.

Bad or corroded contact at the ECM? and exactly where is the EGR -- as you know room and accessibility is at a premium around the engine..

Took one plug out and as expected it was black as Toby's A$$.

C.

Also need to know where to find the temp sensors mentioned.

Thanks.

C.

After tests, scans, and head-scratching: it's running fine and no more "rich" .....  (no codes either)

I'm chasing a ghost.

C.