I have a 96 F150 with a inline 6 , the check engine light came on to day , and I had the code check. can any one tell me what this means. (Catalyst Efficiency below threshold bank 1?)

 

It means the first cat (the reduction cat) on the L fork of the Y-pipe may be contaminated or shattered. If you TAP it (don't HIT it) with a rubber-faced hammer, does it sound like loose stuff rattling around inside?

 

Yes it rattling around.

 

Then the ceramic honeycomb substrate is broken, blocking the exhaust. You should have it replaced soon - it's giving you too much backpressure in those cylinders, and may eventually clog the second cat with its broken pieces, costing you still more.

 

Cats don't usually fry for no reason. I would do a little checking to see if you have a condition that lets extra raw fuel into your exhaust. If you have acess to a engine analizer (ocilliscope) i would check for a cylinder that has low firing kv's. Your local high school shop probably has one, and you may be able to have the students run a test for free. I have used scopes before and have seen a honda accord just about ruin it's cat because of low kv's and misfire in two of it's cylindars. Sorry about the spelling errors, it's still summer vacation!

 

A cat running over temp will show discoloration on the housing, and the substrate will powder - not usually shatter. A shattered cat is more likely the result of physical impact (dented housing or exhaust pipe) or water being pumped in by the smog pump (deep fording).

If the coil was putting out a low-voltage spark, it would test bad using the Haynes procedure which can be done at home with a $10 multimeter in a few minutes. Haynes also tells how to diagnose other problems that would result in a rich condition in the exhaust, but the HEGO would certainly report it to the EEC, and it would show a code for it. Since gene's doesn't , I think it's just an impact that caused it.