New exhaust + O2 sensor problems

Hey everyone, I put a new exhaust w high flow cat + new O2 sensor on my 97, and the truck ran like crap and threw an o2 sensor code saying no change in voltage, so I exchanged the o2 sensor for a new one and got a DIFFERENT o2 code saying "constant lean condition" but it ran slightly better, but sucks gas and smells nasty. I replaced the MAP sensor to make sure it was not the culprit, and still same. Seems to drive fine, but at idle it runs crummy, stinks, and I've lost about 50% of my fuel economy since the new pipes and sensors. Any Ideas??

Where'd you get the O2 sensor? They might have given you the wrong one, never trust the counter drone at a parts chain. It sounds like the engine is never leaving open loop mode or is running way too rich for some other reason - probably the O2 sensor. Also, try reseating the connectors, clean them out with contact cleaner and check to make sure none of the wires are shorting against anything - the wires down near the rear O2 sensor often come in contact with the exhaust and melt through the insulation.

Ive replaced that sensor twice now, with a Bosch from Auto Zone and and exchange from the same store, and checked the part number as they were looking it up... conectors and wires are all like new down there, there is a plastic guide that holds the connector and wires up against the floor pan away from the drv shaft and cat. I don't know if it is significant, but I ran the truck for months with the original cat that was rattling like a can of marbles, and muffler that was split at the seam because of money issues, and the truck ran poorly like the exhaust was plugged, but no rough idle or codes, and gas was much better then. Now the truck runs MUCH nicer with the new system but with all the problems mentioned above. I cant sort out the poor air fuel mixture problem... I did put in nice new platinum plugs, and like to fix problem before fouling them. LOL

The only other clue that might shed some light is that after getting the old cat off, and not being able to get the old o2 sensor out I did drive the truck sans cat and muffler approximately 1 mile to the part store, and 1 mile back. Could I have screwed up something by driving it with a completely open system for a couple of miles? I didn't thrash around in it like that, simply to the store and back.

Check the MAT, if shorted to ground that will cause lean condition.

Are you SURE there are no intake leaks? Quite common to not get the intake manifold seated correctly on the dowels.

Last, try removing both cables from the battery terminals and holding them together for 30 seconds to completely reset the electronics. Remember remove BOTH cables, don't try and disconnect just one and then short it to the other--you won't be happy!

I will look at the MAT.... No intake leaks, I am running a K&N CAI that was there when I bought the Jeep, and never a problem, and just put on the Eastern High flo factory replacement CAT, and a Dynomax cat back. There were no problems before the new pipes went on, so I don't think anything on the intake sise was a problem. I did the new MAP from advice I got when 2 new o2 sensors did not fix the problem. COULD IT BE AN UPSTREAM o2 sensor BAD?

Do you have the 49 state or CA emissions? How many o2 sensors? Usually the downstream sensor isn't a problem, the upstream sensor will give you problems more than the downstream.

I'm in Jersey, one of the other 49 states... LOL

It just makes me scratch my head that fixing the exhaust problem caused some OTHER problem... UGH

Going to start testing more tomorrow. I found some good general info about testing the upstream O2 sensor, and other stuff. If anyone has any good tests I can try to find out what could be hosing the air/fuel ratio when hot, please post suggestions. Runs great in open loop, only acts up in closed loop.